WSRM provides automatic resource management based on predefined or custom policies. You use WSRM to manage both CPU and memory resources. Of course, you can already manage storage resources using the quota system that has appeared in all versions of Windows Server. In many respects, WSRM follows the policy setup used by Windows security. The policy modifies how the system interacts with entities using the resource.
The policies used by WSRM don’t take effect until the server reaches 70 percent capacity in the affected area. For example, when the server is at only 20 percent CPU usage, the policy isn’t used. Microsoft never tells why it chose the 70 percent level, but anecdotal evidence suggests that contention becomes troublesome at that level on Windows servers. You use WSRM to manage resources in the following ways:
• Manage system resources on a constant or scheduled basis using predefined or custom policies.
• Use calendar rules to specify different policies at different times.
• Select the appropriate policy based on server properties, events, changes to the amount of memory installed, or changes to the number of available processors.
• Obtain resource usage data and store it locally or within a centrally located SQL Server database.
The biggest benefit of resource management is to help make the server available even under significant load. Although a server that has a single role probably won’t need WSRM, adding additional roles complicates the server setup and makes management valuable. In addition, using WSRM can help extend the useful life of older servers by reducing contention for valuable resources. Users tend to see slower, but consistent, response times with the appropriate policies in place. Processes don’t end up starved for resources, which makes the server more reliable.
The Resource Allocation Policies folder contains all the policies used to manage resources on the server. WSRM comes with four predefined policies. The following list describes these four policies:
• Equal_Per_Process: Each running process receives an equal portion of CPU and memory resources. This default policy limits each process to a maximum of 10 percent of the available resources while the resource usage remains above 70 percent (the contention level). This is the default managing policy. You normally use this policy for service-related servers, such as those that provide file and print services.
• Equal_Per_User: Each user receives an equal share of CPU and memory resources. For example, if the server is servicing ten users, each user receives 10 percent of the available resources while the resource usage remains above 70 percent. You normally use this policy for application servers.
• Equal_Per_IISAppPool: Each Internet Information Server (IIS) application pool receives an equal share of CPU and memory resources. Applications that aren’t part of an IIS application pool receive any resources that are left over from IIS activities. In some cases, this means that services and server-based applications won’t receive any resources while IIS is under heavy load. You normally use this policy for Web servers or for servers that provide Web services.
• Equal_Per_Session: Each session receives an equal share of the CPU and memory resources. For example, if the server is servicing ten sessions, each session receives 10 percent of the available resources while the resource usage remains above 70 percent. Because a user can have multiple sessions, this policy isn’t the same as the Equal_Per_User policy. Users with multiple sessions receive preferential treatment when using this policy. You normally use this policy for servers that support Terminal Services.
These default policies serve as a basis for common resource management scenarios, but may not meet your needs. For example, you may want to give a particular application preferential treatment to ensure that users can always access it — address this requirement using a custom policy.
Policies also have a scope. You can assign a policy at the system level so that it affects every application, session, or user on the system. As an alternative, you can create a conditional scope specifying that WSRM uses a policy to meet a specific need. Setting conditional policies can become quite complex and usually reflects a special setup on your server.
In some cases, the server doesn’t have the same load placed on it every day. A server may need to perform specific tasks based on calendar requirements. For example, an accounting computer may have to give priority to performing end-of-month calculations at the end of the month. To set a onetime or recurring policy event, choose the Calendar folder. This feature works precisely the same way as the Calendar feature in Outlook. Simply right-click the calendar area, choose the kind of event you want to create, and set the date and time parameters.
Source of Information : For Dummies Windows Server 2008 For Dummies
Showing posts with label Networking. Show all posts
Showing posts with label Networking. Show all posts
Working with the Windows System Resource Manager (WSRM)
The Windows System Resource Manager (WSRM) is a tool that you can install and use no matter which configuration of Windows Server 2008 you use. When you’re working in a workgroup setting, the main purposes for WSRM are to monitor Terminal Services connections and to manage resource usage by applications. In a domain environment, WSRM also helps you keep tight control over how the system and users work with resources. Using this tool helps you create an environment where everyone gets their fair share of resources. Of course, you can weight the usage depending on the criticality of the resource need.
To use WSRM, you must install the Windows System Resource Manager feature. When you check the Windows System Resource Manager feature, you see the Add Features Wizard dialog box, telling you that you must install the Windows Internal Database feature as well. Click Add Required Feature to add this feature, if you haven’t already installed it.
After you install WSRM, you see a new Windows System Resource Manager entry in the Administrative Tools folder. Opening the Windows System Resource Manager console displays the Connection to Computer dialog box, where you can choose the local computer or another computer on the network to manage. This section uses the local computer as an example, but the techniques shown work with other Windows Server 2008 computers as well. Choosing a connection displays the resources for the computer you select.
The functionality provided by WSRM is new for Windows Server 2008. WSRM is such a useful console that you want to consider using it for heavily loaded systems or for networks that tend to become overwhelmed.
Source of Information : For Dummies Windows Server 2008 For Dummies
To use WSRM, you must install the Windows System Resource Manager feature. When you check the Windows System Resource Manager feature, you see the Add Features Wizard dialog box, telling you that you must install the Windows Internal Database feature as well. Click Add Required Feature to add this feature, if you haven’t already installed it.
After you install WSRM, you see a new Windows System Resource Manager entry in the Administrative Tools folder. Opening the Windows System Resource Manager console displays the Connection to Computer dialog box, where you can choose the local computer or another computer on the network to manage. This section uses the local computer as an example, but the techniques shown work with other Windows Server 2008 computers as well. Choosing a connection displays the resources for the computer you select.
The functionality provided by WSRM is new for Windows Server 2008. WSRM is such a useful console that you want to consider using it for heavily loaded systems or for networks that tend to become overwhelmed.
Source of Information : For Dummies Windows Server 2008 For Dummies
Understanding Domains
Domains predate the workgroup by a considerable time-span in computer years. Older computer systems used a centralized mainframe and terminals attached to the mainframe to perform work. In many respects, a Windows domain works the same way as these systems of old. Yes, the workstations connected to the server have intelligence and perform some work locally, but the central computer maintains a firm grip on everything that goes on with the network. That’s why administrators call servers that provide services in a domain a domain controller — the server controls the environment completely.
Don’t get visions of “Big Brother” at this point. Yes, the domain controller exercises considerable control over the network, but many users won’t even notice the difference. The difference is more noticeable to the administrator than it is to the user in most cases. Domains are extremely useful in some situations. You have many reasons for using a domain. These reasons include
• Better security
• Centralization of control over users, machines, and resources
• Improved organizational capability
• Enhanced performance through efficient resource usage
• Superior reliability on large networks
This list may lead you to believe that domains are far superior to workgroups, and they are, in some respects. However, you always have to consider both sides of the coin. Although domains provide you with all these benefits, you must also bear the cost of using them. These costs include
• Increased complexity, which can increase administration time and result in more errors
• Loss of certain Windows Server 2008 features, such as Internet Connection Sharing (ICS)
• Required use of some features, such as Active Directory
• Significantly increased training costs
• Decreased flexibility in some areas, such as the ability to create ad hoc connections when required
• The number of users makes a difference. (I’ve seen networks of up to 100 users work just fine as a workgroup, but 75 users is probably a more practical upper limit.)
• Application types, such as databases, require better security and control, which means that you may need a domain with fewer users.
• High-network-bandwidth applications require additional resources, which means you may need a domain with fewer users.
• High-security applications normally require a domain no matter how few or many users you have.
• Shared resource applications, such as word processing, don’t require a domain in most cases unless you have a large number of users that must collaborate on content.
• Services such as file sharing and printing don’t usually require a domain.
• Power users generally work better in a workgroup setup.
• Novice users may not require a domain, but the domain environment can sometimes prevent them from making as many mistakes.
• Scientific and other highly collaborative applications don’t require a domain unless the application has significant security requirements. (The use of a domain will inhibit the users in this case.)
• Networks with high growth rates may not require a domain today, but will likely need one tomorrow, so installing the domain at the outset is less confusing for end users.
Domains are a good networking solution, but only in certain situations. In some cases, a workgroup is the right choice because the number of users doesn’t warrant a domain. Of the factors that you should consider when choosing between a domain and a workgroup, the centralized management capability is the most significant reason to use a domain, whereas the increase in complexity is the most significant reason not to use a domain. No magic number of users exists for determining when to use a domain. The point at which a domain becomes necessary is a combination of the following user factors:
Source of Information : For Dummies Windows Server 2008 For Dummies
Don’t get visions of “Big Brother” at this point. Yes, the domain controller exercises considerable control over the network, but many users won’t even notice the difference. The difference is more noticeable to the administrator than it is to the user in most cases. Domains are extremely useful in some situations. You have many reasons for using a domain. These reasons include
• Better security
• Centralization of control over users, machines, and resources
• Improved organizational capability
• Enhanced performance through efficient resource usage
• Superior reliability on large networks
This list may lead you to believe that domains are far superior to workgroups, and they are, in some respects. However, you always have to consider both sides of the coin. Although domains provide you with all these benefits, you must also bear the cost of using them. These costs include
• Increased complexity, which can increase administration time and result in more errors
• Loss of certain Windows Server 2008 features, such as Internet Connection Sharing (ICS)
• Required use of some features, such as Active Directory
• Significantly increased training costs
• Decreased flexibility in some areas, such as the ability to create ad hoc connections when required
• The number of users makes a difference. (I’ve seen networks of up to 100 users work just fine as a workgroup, but 75 users is probably a more practical upper limit.)
• Application types, such as databases, require better security and control, which means that you may need a domain with fewer users.
• High-network-bandwidth applications require additional resources, which means you may need a domain with fewer users.
• High-security applications normally require a domain no matter how few or many users you have.
• Shared resource applications, such as word processing, don’t require a domain in most cases unless you have a large number of users that must collaborate on content.
• Services such as file sharing and printing don’t usually require a domain.
• Power users generally work better in a workgroup setup.
• Novice users may not require a domain, but the domain environment can sometimes prevent them from making as many mistakes.
• Scientific and other highly collaborative applications don’t require a domain unless the application has significant security requirements. (The use of a domain will inhibit the users in this case.)
• Networks with high growth rates may not require a domain today, but will likely need one tomorrow, so installing the domain at the outset is less confusing for end users.
Domains are a good networking solution, but only in certain situations. In some cases, a workgroup is the right choice because the number of users doesn’t warrant a domain. Of the factors that you should consider when choosing between a domain and a workgroup, the centralized management capability is the most significant reason to use a domain, whereas the increase in complexity is the most significant reason not to use a domain. No magic number of users exists for determining when to use a domain. The point at which a domain becomes necessary is a combination of the following user factors:
Source of Information : For Dummies Windows Server 2008 For Dummies
Working with Peer Name Resolution Protocol
The Peer Name Resolution Protocol (PNRP) is the basis for connectivity between peers in a workgroup. Every computer in a network has to be able to identify every other computer. You wouldn’t want to connect to Computer A one time and to Computer B another time because they both have the same name or the network confuses them in some way. Reliable connections ensure that everyone connects to the same machine every time.
A workgroup often experiences problems with standard methods of machine identification, such as using the Domain Name System (DNS). That’s the reason Microsoft has created PNRP — to overcome identification difficulties. PNRP provides these benefits:
• Distributed identification that doesn’t rely on a central server
• Support for as many names as the network requires
• Name publications without the use of third-party products or third-party servers
• Real-time identification updates
• Support for naming all device types, not just computers
• Protected name publication so that you don’t have to worry about someone else grabbing your name
The best part about PNRP is that you normally don’t have to do anything special to use it. The only potential problem is that you must ensure that the Computer Browser service is running and that all workstations that share resources also have the Server service running. If these two services are running, you probably won’t experience any problems with PNRP. You can read the full technical details of PNRP at http://technet.microsoft.com/en-us/library/bb726971.aspx.
Source of Information : For Dummies Windows Server 2008 For Dummies
A workgroup often experiences problems with standard methods of machine identification, such as using the Domain Name System (DNS). That’s the reason Microsoft has created PNRP — to overcome identification difficulties. PNRP provides these benefits:
• Distributed identification that doesn’t rely on a central server
• Support for as many names as the network requires
• Name publications without the use of third-party products or third-party servers
• Real-time identification updates
• Support for naming all device types, not just computers
• Protected name publication so that you don’t have to worry about someone else grabbing your name
The best part about PNRP is that you normally don’t have to do anything special to use it. The only potential problem is that you must ensure that the Computer Browser service is running and that all workstations that share resources also have the Server service running. If these two services are running, you probably won’t experience any problems with PNRP. You can read the full technical details of PNRP at http://technet.microsoft.com/en-us/library/bb726971.aspx.
Source of Information : For Dummies Windows Server 2008 For Dummies
Considering Centralized versus Group Sharing
One of the most important preparation steps for your server is determining how to store the data you create. The two common methods are centralized and group sharing:
• Centralized sharing involves placing all data in one location. You can organize the data into folders to keep various projects separate, but everything appears under one main folder or on a particular hard drive.
• Group sharing involves placing data in multiple locations based on who creates it and who needs to work with it next. Every workstation could have an inbox to hold files that the person needs to work on next. Each person can also have private data stores for files that no one else will need.
The sharing methods aren’t mutually exclusive: You may choose to provide centralized sharing for your word-processed files but provide group sharing for graphics files. The technique you choose depends greatly on how your organization uses the data. If everyone collaborates on word-processed files, then centralized sharing makes sense.
Centralized sharing provides advantages over group sharing. For example, it’s easier to locate files when everyone knows where the files appear on the network. In addition, you can back up and restore centralized files with greater ease. Security also becomes less cumbersome because you don’t have to open as many areas to common access.
Before you get the idea that group sharing isn’t useful, you should know it also provides some essential workgroup functionality. A group sharing strategy can prove quite useful in workflow scenarios where data flows from one person to the next. Only the two people involved in the data transfer actually need access to the data storage area, so this approach reduces potential security problems by reducing the number of people with access to the data. When working with private data, only the person who actually needs to work with the data has access to it. You can therefore secure confidential documents with greater ease.
It’s easy to find reasons to use one or the other sharing strategy in a particular situation. In some cases, you won’t find a perfect strategy unless you mix elements of both. For example, when working with word-processed files, you might collaborate on a document with your peers and then move the document from the centralized sharing area to the inbox of someone who will prepare the document for printing. An editor might review the document for grammar and spelling issues and then move the file to the inbox of a compositor who prepares the document in PDF form. Eventually, someone prints the final document. In this case, you use a combination of strategies to ensure the document is prepared in a timely manner.
Source of Information : For Dummies Windows Server 2008 For Dummies
• Centralized sharing involves placing all data in one location. You can organize the data into folders to keep various projects separate, but everything appears under one main folder or on a particular hard drive.
• Group sharing involves placing data in multiple locations based on who creates it and who needs to work with it next. Every workstation could have an inbox to hold files that the person needs to work on next. Each person can also have private data stores for files that no one else will need.
The sharing methods aren’t mutually exclusive: You may choose to provide centralized sharing for your word-processed files but provide group sharing for graphics files. The technique you choose depends greatly on how your organization uses the data. If everyone collaborates on word-processed files, then centralized sharing makes sense.
Centralized sharing provides advantages over group sharing. For example, it’s easier to locate files when everyone knows where the files appear on the network. In addition, you can back up and restore centralized files with greater ease. Security also becomes less cumbersome because you don’t have to open as many areas to common access.
Before you get the idea that group sharing isn’t useful, you should know it also provides some essential workgroup functionality. A group sharing strategy can prove quite useful in workflow scenarios where data flows from one person to the next. Only the two people involved in the data transfer actually need access to the data storage area, so this approach reduces potential security problems by reducing the number of people with access to the data. When working with private data, only the person who actually needs to work with the data has access to it. You can therefore secure confidential documents with greater ease.
It’s easy to find reasons to use one or the other sharing strategy in a particular situation. In some cases, you won’t find a perfect strategy unless you mix elements of both. For example, when working with word-processed files, you might collaborate on a document with your peers and then move the document from the centralized sharing area to the inbox of someone who will prepare the document for printing. An editor might review the document for grammar and spelling issues and then move the file to the inbox of a compositor who prepares the document in PDF form. Eventually, someone prints the final document. In this case, you use a combination of strategies to ensure the document is prepared in a timely manner.
Source of Information : For Dummies Windows Server 2008 For Dummies
Preparing to Create a Workgroup
The “Understanding Workgroups” section of this chapter describes workgroups and how you can benefit from them and avoid their limitations. A workgroup isn’t always the right solution to your networking needs, even when it provides the ease-of-configuration that you need. Consequently, your first step in preparing to create a workgroup is determining whether a workgroup is the right solution. If your network meets these requirements, you can probably use a workgroup to solve your basic networking needs:
• It provides basic file and printer sharing.
• (Optional) It provides basic database management support with no more than two custom applications.
• (Optional) It provides e-mail support with a product such as Exchange Server.
• (Optional) It provides centralized Internet access.
• It has no need for complex mission-critical applications involving large databases.
• It has no need for centralized resource management.
• It requires no remote access.
• It has no need to support external applications, a Web site, or Web services.
• It needs no more than 100 nodes in most cases.
After you determine whether you actually need a workgroup configuration, it’s time to spend some time figuring out the details. Remember that a workgroup is made up of peers. Consequently, you don’t have to have one machine that does everything. Don’t be afraid to create a plan that emphasizes the strengths of each machine in the workgroup, even if you plan to use a server. The server should provide centralized storage, but any other machine can support any other task. In fact, it may be beneficial to spread out the tasks so that the server doesn’t become overwhelmed trying to perform every task.
Create a list of the machines you plan to connect, the resources each machine can provide, and the location of each machine. You can use this list as a planning guide for configuring the network later. Make sure to consider the tasks that each machine will normally perform so that you don’t overload it. If the workstations in a workgroup are overloaded, consider getting a dedicated server to reduce some of the load. Obtain a server that can handle the current load plus at least twice as much additional load for future expansion. Most companies find that their server becomes too small, quite quickly if they don’t obtain enough capacity for future needs.
Although the topic is outside the scope of this book, you also need to consider the physical requirements of the network. The network will likely require switches, NICs, cabling (unless you plan to go wireless), and other physical elements. The kind of cabling you choose is also important because the cable must provide support for the network speed you choose or you’ll experience errors in transmitting the data. Whenever possible, use switches instead of hubs because switches have intelligence built into them that makes them more reliable and faster. Some companies don’t consider these issues and end up with cost overruns as a result. If you use a consultant to perform the physical configuration, make sure to plan for the consulting costs and add a little cushion in case the consultant encounters unanticipated problems.
Survey all the applications you need to run and consider these applications as part of the network setup. In many cases, you need to reconfigure the applications to run properly on the network. For example, Office users will likely want to store their data files in a central location so that everyone in the workgroup can access them. The centralized storage requires additional configuration time, and you need to plan for it as part of your preparation.
One of the issues that administrators tend to run into is that everyone wants to add special gizmos to the network simply because they can and not because they require the gizmos. Avoid gizmos when you can because they usually spell trouble. The more gizmos you have, the more complex your network becomes and the more time you spend securing, configuring, and maintaining it. Gizmos add to support costs and usually make users less productive. In short, gizmos are usually a waste of time, effort, and money, so you should avoid them.
Source of Information : For Dummies Windows Server 2008 For Dummies
• It provides basic file and printer sharing.
• (Optional) It provides basic database management support with no more than two custom applications.
• (Optional) It provides e-mail support with a product such as Exchange Server.
• (Optional) It provides centralized Internet access.
• It has no need for complex mission-critical applications involving large databases.
• It has no need for centralized resource management.
• It requires no remote access.
• It has no need to support external applications, a Web site, or Web services.
• It needs no more than 100 nodes in most cases.
After you determine whether you actually need a workgroup configuration, it’s time to spend some time figuring out the details. Remember that a workgroup is made up of peers. Consequently, you don’t have to have one machine that does everything. Don’t be afraid to create a plan that emphasizes the strengths of each machine in the workgroup, even if you plan to use a server. The server should provide centralized storage, but any other machine can support any other task. In fact, it may be beneficial to spread out the tasks so that the server doesn’t become overwhelmed trying to perform every task.
Create a list of the machines you plan to connect, the resources each machine can provide, and the location of each machine. You can use this list as a planning guide for configuring the network later. Make sure to consider the tasks that each machine will normally perform so that you don’t overload it. If the workstations in a workgroup are overloaded, consider getting a dedicated server to reduce some of the load. Obtain a server that can handle the current load plus at least twice as much additional load for future expansion. Most companies find that their server becomes too small, quite quickly if they don’t obtain enough capacity for future needs.
Although the topic is outside the scope of this book, you also need to consider the physical requirements of the network. The network will likely require switches, NICs, cabling (unless you plan to go wireless), and other physical elements. The kind of cabling you choose is also important because the cable must provide support for the network speed you choose or you’ll experience errors in transmitting the data. Whenever possible, use switches instead of hubs because switches have intelligence built into them that makes them more reliable and faster. Some companies don’t consider these issues and end up with cost overruns as a result. If you use a consultant to perform the physical configuration, make sure to plan for the consulting costs and add a little cushion in case the consultant encounters unanticipated problems.
Survey all the applications you need to run and consider these applications as part of the network setup. In many cases, you need to reconfigure the applications to run properly on the network. For example, Office users will likely want to store their data files in a central location so that everyone in the workgroup can access them. The centralized storage requires additional configuration time, and you need to plan for it as part of your preparation.
One of the issues that administrators tend to run into is that everyone wants to add special gizmos to the network simply because they can and not because they require the gizmos. Avoid gizmos when you can because they usually spell trouble. The more gizmos you have, the more complex your network becomes and the more time you spend securing, configuring, and maintaining it. Gizmos add to support costs and usually make users less productive. In short, gizmos are usually a waste of time, effort, and money, so you should avoid them.
Source of Information : For Dummies Windows Server 2008 For Dummies
Understanding Workgroups
The workgroup was the original form of networking supported by Windows, and it’s really still the basic form of all Windows networking. The concept of a workgroup was originally defined around peer-to-peer networking, where any machine on a network can act as a server and any machine can act as a workstation. Even today, Windows Server 2008 has both the Server and the Workstation services that provide these two roles. You can use your Windows Server 2008 server as a workstation if you want — no one can honestly say that this functionality is unavailable. Of course, Microsoft now has the Server Core version of Windows Server 2008. Theoretically, you can use Server Core as a workstation, but I don’t know of anyone who’d want to.
The other standard form of networking is client/server. In this form of networking, you don’t use the server as a workstation. In fact, when working with operating systems such as NetWare (http://www.novell.com/products/netware/), you can’t use the machine that has the operating system installed as a workstation. It’s simply impossible to use a NetWare server as a workstation because no functionality exists to do it. The advantage of client/server setups is that they’re very light and reliable. The server uses all its resources to perform tasks on behalf of the client. However, this form of networking lacks flexibility. All workstations are always workstations, and all servers are always servers.
Understanding the pros of workgroups
Workgroups are convenient because you don’t have to have one super machine to handle everyone’s requests. Any workstation can also act as a server, so you can attach a laser printer to one workstation and an inkjet to another workstation. With the proper settings, everyone has access to both printers even though the printers appear on different machines. Sharing occurs on many levels. A workstation with an exceptionally large hard drive can share some of that hard drive space with everyone on the network. Likewise, a workstation with an Internet connection can share the connection with everyone else. Peer-to-peer networking is all about sharing whatever a workstation has in excess with everyone else on the network so that everyone benefits from that excess.
Most administrators also find workgroups easier to manage, at least when they’re small. If someone wants access to a particular workstation, their name must appear on the list of users for that workstation. When a workstation wants to share a particular asset, you must configure that asset for sharing and define who can use it. All of the settings are localized and easy to understand. You don’t have to worry about global security policies, Active Directory, or anything else that’s overly complicated.
A workgroup need not exist as a separate entity. You can use a workgroup network setup at the departmental level and a domain or client/server setup at the enterprise level. The concepts behind a workgroup work equally well in the departmental environment as they do in standalone mode. One question with workgroups is finding out how large can you make them before they reach their limit. The best way to answer this question is to determine how the administrator configures the workgroup, know whether the workgroup contains the proper number of dedicated servers, and what you expect the workgroup to do. If your only goal for the workgroup is to share files and print documents, a workgroup of any size is possible. As you add tasks, such as database management, the potential size for a workgroup decreases because you’re asking it to perform more work. A workgroup configuration that includes e-mail, file, print, and database management services is probably limited to 100 nodes. However, a skillful administrator could potentially increase that size.
Understanding the cons of workgroups
Using a workgroup becomes less advantageous when you begin using a number of custom applications and require centralized management for help desk support and other needs. Adding remote users and other enterprise requirements increase complexity and the need for centralized management, which usually means obtaining a central management application. For example, if you plan to use Microsoft’s System Center Operations Manager, or SCOM (http://www.microsoft.com/systemcenter/opsmgr/default.mspx), you need a domain. Consequently, the workgroup meets its match in complexity, not necessarily in size.
Workgroups also tend to provide poorer security than does a centralized network (client/server or domain). Because everyone is sharing resources freely, it can be difficult to lock down those resources and ensure that they’re shared only as required to accomplish tasks within the workgroup. Because of the poorer security, workgroups often encounter problems with adware and viruses where one machine’s woe automatically becomes every machine’s woe.
Source of Information : For Dummies Windows Server 2008 For Dummies
The other standard form of networking is client/server. In this form of networking, you don’t use the server as a workstation. In fact, when working with operating systems such as NetWare (http://www.novell.com/products/netware/), you can’t use the machine that has the operating system installed as a workstation. It’s simply impossible to use a NetWare server as a workstation because no functionality exists to do it. The advantage of client/server setups is that they’re very light and reliable. The server uses all its resources to perform tasks on behalf of the client. However, this form of networking lacks flexibility. All workstations are always workstations, and all servers are always servers.
Understanding the pros of workgroups
Workgroups are convenient because you don’t have to have one super machine to handle everyone’s requests. Any workstation can also act as a server, so you can attach a laser printer to one workstation and an inkjet to another workstation. With the proper settings, everyone has access to both printers even though the printers appear on different machines. Sharing occurs on many levels. A workstation with an exceptionally large hard drive can share some of that hard drive space with everyone on the network. Likewise, a workstation with an Internet connection can share the connection with everyone else. Peer-to-peer networking is all about sharing whatever a workstation has in excess with everyone else on the network so that everyone benefits from that excess.
Most administrators also find workgroups easier to manage, at least when they’re small. If someone wants access to a particular workstation, their name must appear on the list of users for that workstation. When a workstation wants to share a particular asset, you must configure that asset for sharing and define who can use it. All of the settings are localized and easy to understand. You don’t have to worry about global security policies, Active Directory, or anything else that’s overly complicated.
A workgroup need not exist as a separate entity. You can use a workgroup network setup at the departmental level and a domain or client/server setup at the enterprise level. The concepts behind a workgroup work equally well in the departmental environment as they do in standalone mode. One question with workgroups is finding out how large can you make them before they reach their limit. The best way to answer this question is to determine how the administrator configures the workgroup, know whether the workgroup contains the proper number of dedicated servers, and what you expect the workgroup to do. If your only goal for the workgroup is to share files and print documents, a workgroup of any size is possible. As you add tasks, such as database management, the potential size for a workgroup decreases because you’re asking it to perform more work. A workgroup configuration that includes e-mail, file, print, and database management services is probably limited to 100 nodes. However, a skillful administrator could potentially increase that size.
Understanding the cons of workgroups
Using a workgroup becomes less advantageous when you begin using a number of custom applications and require centralized management for help desk support and other needs. Adding remote users and other enterprise requirements increase complexity and the need for centralized management, which usually means obtaining a central management application. For example, if you plan to use Microsoft’s System Center Operations Manager, or SCOM (http://www.microsoft.com/systemcenter/opsmgr/default.mspx), you need a domain. Consequently, the workgroup meets its match in complexity, not necessarily in size.
Workgroups also tend to provide poorer security than does a centralized network (client/server or domain). Because everyone is sharing resources freely, it can be difficult to lock down those resources and ensure that they’re shared only as required to accomplish tasks within the workgroup. Because of the poorer security, workgroups often encounter problems with adware and viruses where one machine’s woe automatically becomes every machine’s woe.
Source of Information : For Dummies Windows Server 2008 For Dummies
DHCP Message Format
The fields in the DHCP message are the following:
• Message Op Code (Op) A 1-byte field that indicates whether the message is a request
(set to 1) or a reply (set to 2).
• Hardware Address Type (Htype). A 1-byte field that indicates the type of hardware being used by the DHCP client. This field uses the same values as the Hardware Type field in the Address Resolution Protocol (ARP) header. For a complete list of ARP Hardware Type values, see http://www.iana.org/assignments/arp-parameters.
• Hardware Address Length (Hlen). A 1-byte field that indicates the number of highorder bytes within the fixed-length Client Hardware Address field that contains the client’s hardware address. For commonly used IEEE 802-based technologies, such as Ethernet and IEEE 802.11, the value of this field is 6.
• Hops. A 1-byte field that indicates how many DHCP relay agents have forwarded the message. The initial value is 0. When a DHCP relay agent forwards a DHCP message on behalf of either a DHCP client or a DHCP server, it increments this field. The maximum number of hops in a DHCP infrastructure is 16. If the value is greater than 16, the receiving DHCP relay agent silently discards the message. DHCP relay agents can also discard DHCP messages if this field exceeds a configurable value. For example, the DHCP Relay Agent component of Routing and Remote Access in Windows Server 2008 uses a default maximum of 4 hops.
• Transaction ID (Xid). A 4-byte field that contains a random number derived by the
DHCP client to group all of the DHCP messages of a given message exchange together, such as all of the messages for a lease acquisition.
• Seconds (Secs). A 2-byte field set by the DHCP client to indicate the number of seconds that have elapsed since the client began the address acquisition process.
• Flags. A 2-byte field that indicates flags that are set by the DHCP client. RFC 2131 defines the high-order bit as the Broadcast flag. A DHCP client uses the broadcast flag to indicate that it can (set to 0) or cannot (set to 1) receive unicast IP datagrams even though it has not been configured with an IP address. Windows Server 2008 and Windows Vista-based DHCP clients set the Broadcast flag to 1 (responses must be broadcast). If the DHCP server has been configured to process this flag, it will send its response as either a unicast (when the Broadcast flag is set to 0) or as a broadcast (when the Broadcast
flag is set to 1).
• Client IP. Address (Ciaddr) A 4-byte field that indicates a DHCP client’s IP address. This field is set by the DHCP client in DHCP messages when it has been successfully configured with the IP address and can respond to ARP requests to defend the use of the address.
• Your IP. Address (Yiaddr). A 4-byte field that indicates the IP address that is being allocated to the DHCP client by the DHCP server.
• Server IP Address (Siaddr). A 4-byte field that indicates the IP address of the DHCP server that is offering an IP address.
• Gateway IP Address (Giaddr). A 4-byte field that indicates an IP address that is assigned to the interface on the initial DHCP relay agent that received the message from the DHCP client. The initial DHCP relay agent is located on the same subnet as the DHCP client that broadcast the DHCP request message (either a DHCPDISCOVER or DHCPREQUEST message). By recording an IP address for the subnet of the DHCP client in this field, the DHCP server can determine the proper scope from which to assign an IP address to the requesting DHCP client.
• Client Hardware Address (Chaddr). A 16-byte field that indicates the hardware address of the DHCP client. To determine how many bytes are used for the hardware address, the DHCP server and relay agent use the value of the Hardware Address Length field. Fo commonly used IEEE 802-based technologies, this field contains the 6-byte media access control (MAC) address of the Ethernet or 802.11 network adapter of the DHCP client and
10 bytes set to 0.
• Server Host Name (Sname). A 64-byte field that indicates a name for the DHCP server.
The DHCP Server service in Windows Server 2008 does not use this field.
• Boot File Name (File). A 128-byte field that indicates the name of the file containing a boot image for a BOOTP client. BOOTP was developed before DHCP to allow a diskless host computer to obtain an IP address configuration, the name of a boot file, and the location of a Trivial File Transfer Protocol (TFTP) server from which the computer loads the boot file. DHCP message exchanges do not use this field.
• Options A variable-length set of fields containing DHCP options.
By default, the DHCP Server service in Windows Server 2008 ignores the Broadcast flag in the Flags field of broadcast-based DHCP messages received by DHCP clients. To configure the DHCP Server service to process the Broadcast flag, create and set theIgnoreBroadcastFlag registry value to 0.
Source of Information : Microsoft Press Windows Server 2008 TCP IP Protocols and Services
• Message Op Code (Op) A 1-byte field that indicates whether the message is a request
(set to 1) or a reply (set to 2).
• Hardware Address Type (Htype). A 1-byte field that indicates the type of hardware being used by the DHCP client. This field uses the same values as the Hardware Type field in the Address Resolution Protocol (ARP) header. For a complete list of ARP Hardware Type values, see http://www.iana.org/assignments/arp-parameters.
• Hardware Address Length (Hlen). A 1-byte field that indicates the number of highorder bytes within the fixed-length Client Hardware Address field that contains the client’s hardware address. For commonly used IEEE 802-based technologies, such as Ethernet and IEEE 802.11, the value of this field is 6.
• Hops. A 1-byte field that indicates how many DHCP relay agents have forwarded the message. The initial value is 0. When a DHCP relay agent forwards a DHCP message on behalf of either a DHCP client or a DHCP server, it increments this field. The maximum number of hops in a DHCP infrastructure is 16. If the value is greater than 16, the receiving DHCP relay agent silently discards the message. DHCP relay agents can also discard DHCP messages if this field exceeds a configurable value. For example, the DHCP Relay Agent component of Routing and Remote Access in Windows Server 2008 uses a default maximum of 4 hops.
• Transaction ID (Xid). A 4-byte field that contains a random number derived by the
DHCP client to group all of the DHCP messages of a given message exchange together, such as all of the messages for a lease acquisition.
• Seconds (Secs). A 2-byte field set by the DHCP client to indicate the number of seconds that have elapsed since the client began the address acquisition process.
• Flags. A 2-byte field that indicates flags that are set by the DHCP client. RFC 2131 defines the high-order bit as the Broadcast flag. A DHCP client uses the broadcast flag to indicate that it can (set to 0) or cannot (set to 1) receive unicast IP datagrams even though it has not been configured with an IP address. Windows Server 2008 and Windows Vista-based DHCP clients set the Broadcast flag to 1 (responses must be broadcast). If the DHCP server has been configured to process this flag, it will send its response as either a unicast (when the Broadcast flag is set to 0) or as a broadcast (when the Broadcast
flag is set to 1).
• Client IP. Address (Ciaddr) A 4-byte field that indicates a DHCP client’s IP address. This field is set by the DHCP client in DHCP messages when it has been successfully configured with the IP address and can respond to ARP requests to defend the use of the address.
• Your IP. Address (Yiaddr). A 4-byte field that indicates the IP address that is being allocated to the DHCP client by the DHCP server.
• Server IP Address (Siaddr). A 4-byte field that indicates the IP address of the DHCP server that is offering an IP address.
• Gateway IP Address (Giaddr). A 4-byte field that indicates an IP address that is assigned to the interface on the initial DHCP relay agent that received the message from the DHCP client. The initial DHCP relay agent is located on the same subnet as the DHCP client that broadcast the DHCP request message (either a DHCPDISCOVER or DHCPREQUEST message). By recording an IP address for the subnet of the DHCP client in this field, the DHCP server can determine the proper scope from which to assign an IP address to the requesting DHCP client.
• Client Hardware Address (Chaddr). A 16-byte field that indicates the hardware address of the DHCP client. To determine how many bytes are used for the hardware address, the DHCP server and relay agent use the value of the Hardware Address Length field. Fo commonly used IEEE 802-based technologies, this field contains the 6-byte media access control (MAC) address of the Ethernet or 802.11 network adapter of the DHCP client and
10 bytes set to 0.
• Server Host Name (Sname). A 64-byte field that indicates a name for the DHCP server.
The DHCP Server service in Windows Server 2008 does not use this field.
• Boot File Name (File). A 128-byte field that indicates the name of the file containing a boot image for a BOOTP client. BOOTP was developed before DHCP to allow a diskless host computer to obtain an IP address configuration, the name of a boot file, and the location of a Trivial File Transfer Protocol (TFTP) server from which the computer loads the boot file. DHCP message exchanges do not use this field.
• Options A variable-length set of fields containing DHCP options.
By default, the DHCP Server service in Windows Server 2008 ignores the Broadcast flag in the Flags field of broadcast-based DHCP messages received by DHCP clients. To configure the DHCP Server service to process the Broadcast flag, create and set theIgnoreBroadcastFlag registry value to 0.
Source of Information : Microsoft Press Windows Server 2008 TCP IP Protocols and Services
Planning for IPv6 Transition Technologies
You will need to use one or more IPv6 transition technologies during the IPv6 migration process. The below provide planning information for ISATAP, 6to4, and Teredo.
ISATAP
By default, ISATAP hosts will obtain the IPv4 address of the ISATAP router by using DNS and other IP name resolution techniques to resolve the name ISATAP to an IPv4 address. Once the host has identified the ISATAP router’s IP address, it uses IPv4 unicast messages to acquire autoconfiguration information from the router. To ensure that clients can find the ISATAP router, plan to use one of the following techniques:
• If the ISATAP router is a computer, configure the computer name as ISATAP.
• Create a DNS entry for every DNS domain.
• Add an entry to the Hosts file.
• Create a static WINS record.
• Run a netsh command on all ISATAP hosts.
6to4
6to4 allows you to access the IPv6 Internet by using your existing IPv4 Internet connection. 6to4 requires you to have a 6to4 router and a public IPv4 address (such as an address assigned by your ISP). IPv4-only routers cannot act as 6to4 routers. Therefore, if you are currently using an IPv4-only router for your Internet access, you will need to upgrade or replace your router. Before investing in upgrades to support 6to4 or Teredo, evaluate whether the benefits of connecting to the IPv6 Internet outweigh the costs. Unless you need to access a specific resource on the IPv6 Internet that is not accessible on the IPv4 Internet, there might be no practical benefit to connecting to the IPv6 Internet. Generally, public IPv6 Internet resources (such as Web sites) are also available on the IPv4 Internet.
Teredo
You can use Teredo to provide hosts with IPv6 Internet connectivity when you do not have a 6to4 router with a public IPv4 address. For best results with Teredo, choose cone or restricted NATs that support UDP port translation, and avoid symmetric NATs. While implementing Teredo, you might discover that you need to change the NAT or firewall configuration. Therefore, you should be prepared to work with network administrators to provide the connectivity you require. You can use Microsoft’s Internet Connectivity Evaluation Tool to determine whether your current NAT supports Teredo. To use the online tool, open http://www.microsoft.com/windows/using/tools/igd/ in Microsoft Windows Internet Explorer, and follow the prompts.
Source of Information : Microsoft Press Windows Server 2008 Networking and Network Access Protection NAP
ISATAP
By default, ISATAP hosts will obtain the IPv4 address of the ISATAP router by using DNS and other IP name resolution techniques to resolve the name ISATAP to an IPv4 address. Once the host has identified the ISATAP router’s IP address, it uses IPv4 unicast messages to acquire autoconfiguration information from the router. To ensure that clients can find the ISATAP router, plan to use one of the following techniques:
• If the ISATAP router is a computer, configure the computer name as ISATAP.
• Create a DNS entry for every DNS domain.
• Add an entry to the Hosts file.
• Create a static WINS record.
• Run a netsh command on all ISATAP hosts.
6to4
6to4 allows you to access the IPv6 Internet by using your existing IPv4 Internet connection. 6to4 requires you to have a 6to4 router and a public IPv4 address (such as an address assigned by your ISP). IPv4-only routers cannot act as 6to4 routers. Therefore, if you are currently using an IPv4-only router for your Internet access, you will need to upgrade or replace your router. Before investing in upgrades to support 6to4 or Teredo, evaluate whether the benefits of connecting to the IPv6 Internet outweigh the costs. Unless you need to access a specific resource on the IPv6 Internet that is not accessible on the IPv4 Internet, there might be no practical benefit to connecting to the IPv6 Internet. Generally, public IPv6 Internet resources (such as Web sites) are also available on the IPv4 Internet.
Teredo
You can use Teredo to provide hosts with IPv6 Internet connectivity when you do not have a 6to4 router with a public IPv4 address. For best results with Teredo, choose cone or restricted NATs that support UDP port translation, and avoid symmetric NATs. While implementing Teredo, you might discover that you need to change the NAT or firewall configuration. Therefore, you should be prepared to work with network administrators to provide the connectivity you require. You can use Microsoft’s Internet Connectivity Evaluation Tool to determine whether your current NAT supports Teredo. To use the online tool, open http://www.microsoft.com/windows/using/tools/igd/ in Microsoft Windows Internet Explorer, and follow the prompts.
Source of Information : Microsoft Press Windows Server 2008 Networking and Network Access Protection NAP
Migrating to IPv6
Upgrading to an exclusively IPv6 environment should be a long-term goal. You will need to follow these general steps (with proper testing prior to any implementation) to migrate to IPv6:
1. As you deploy new computers or operating systems, configure them to support both IPv6 and IPv4. If you plan to continue using computers running Windows XP and Windows Server 2003, gradually enable IPv6 across your infrastructure for those hosts.
2. Upgrade your routing infrastructure to support native IPv6 routing.
3. Upgrade your DNS infrastructure to support IPv6 AAAA records and PTR records in the IP6.ARPA reverse domain.
4. Connect your routing and DNS infrastructures to the IPv6 Internet by using technologies such as 6to4 or Teredo, if necessary.
5. Work with internal and external developers to upgrade your applications to be independent of IPv6 or IPv4.
6. After thorough testing, convert IPv4/IPv6 nodes to use only IPv6.
Of those steps, the single greatest challenge will be upgrading applications to support IPv6. Enterprises often have thousands of applications that must be tested. Many existing applications will not work properly in an IPv6 environment and will need to be either upgraded or replaced before IPv4 can be entirely disabled.
It’s worth remembering that deploying IPv6 is not trivial. Just having IPv6 enabled isn’t a big deal because most of the other devices on your network aren’t going to be using IPv6 (except for other computers running Windows Vista and Windows Server 2008), so if your machine is talking to a printer or other device, it will use just IPv4 by default. Once you start trying to roll out IPv6, though, there is a lot to consider. There are a lot of variables, and not all of the skills you used in IPv4 transfer to IPv6.
You need to plan it out and be ready to troubleshoot during rollout. Maybe some of your applications are just not IPv6 capable, or your older hardware doesn’t understand what an IPv6 address is. Maybe it is a configuration error on a host or router. There could be any number of issues that might cause problems, which is why I strongly recommend setting up an IPv6 test lab now—TODAY!—and testing your devices and applications to determine how they will work in an IPv6 network while building your IPv6 skills.
A lot of people are running IPv6 with Windows and a wide array of stuff and are making it work. To help you get there, we provide tools such as checkv4.exe (available at http://msdn2.microsoft.com/en-us/library/ms740624.aspx) to help you figure out whether your code has any IPv4 calls hardcoded into it, in addition to white papers such as “Manageable Transition to IPv6 using ISATAP” (available at http://www.microsoft.com/downloads/details.aspx?FamilyId=B8F50E07-17BF-4B5C-A1F9-5A09E2AF698B), a joint white paper with Cisco describing how to ease the deployment of IPv6, and “Enabling the Next Generation of Networking with End-to-End IPv6” (available at http://www.microsoft.com/downloads/details.aspx?FamilyID=b3611543-58b5-4ccc-b6ce-677ebb2a520d), a joint white paper with Juniper discussing IPv6 deployment and benefits. All of these and more are available from http://www.microsoft.com/ipv6. In short, we are working with lots of industry partners to simplify IPv6 deployment and make sure that all of our customers can gain the maximum value from IPv6.
Source of Information : Microsoft Press Windows Server 2008 Networking and Network Access Protection NAP
1. As you deploy new computers or operating systems, configure them to support both IPv6 and IPv4. If you plan to continue using computers running Windows XP and Windows Server 2003, gradually enable IPv6 across your infrastructure for those hosts.
2. Upgrade your routing infrastructure to support native IPv6 routing.
3. Upgrade your DNS infrastructure to support IPv6 AAAA records and PTR records in the IP6.ARPA reverse domain.
4. Connect your routing and DNS infrastructures to the IPv6 Internet by using technologies such as 6to4 or Teredo, if necessary.
5. Work with internal and external developers to upgrade your applications to be independent of IPv6 or IPv4.
6. After thorough testing, convert IPv4/IPv6 nodes to use only IPv6.
Of those steps, the single greatest challenge will be upgrading applications to support IPv6. Enterprises often have thousands of applications that must be tested. Many existing applications will not work properly in an IPv6 environment and will need to be either upgraded or replaced before IPv4 can be entirely disabled.
It’s worth remembering that deploying IPv6 is not trivial. Just having IPv6 enabled isn’t a big deal because most of the other devices on your network aren’t going to be using IPv6 (except for other computers running Windows Vista and Windows Server 2008), so if your machine is talking to a printer or other device, it will use just IPv4 by default. Once you start trying to roll out IPv6, though, there is a lot to consider. There are a lot of variables, and not all of the skills you used in IPv4 transfer to IPv6.
You need to plan it out and be ready to troubleshoot during rollout. Maybe some of your applications are just not IPv6 capable, or your older hardware doesn’t understand what an IPv6 address is. Maybe it is a configuration error on a host or router. There could be any number of issues that might cause problems, which is why I strongly recommend setting up an IPv6 test lab now—TODAY!—and testing your devices and applications to determine how they will work in an IPv6 network while building your IPv6 skills.
A lot of people are running IPv6 with Windows and a wide array of stuff and are making it work. To help you get there, we provide tools such as checkv4.exe (available at http://msdn2.microsoft.com/en-us/library/ms740624.aspx) to help you figure out whether your code has any IPv4 calls hardcoded into it, in addition to white papers such as “Manageable Transition to IPv6 using ISATAP” (available at http://www.microsoft.com/downloads/details.aspx?FamilyId=B8F50E07-17BF-4B5C-A1F9-5A09E2AF698B), a joint white paper with Cisco describing how to ease the deployment of IPv6, and “Enabling the Next Generation of Networking with End-to-End IPv6” (available at http://www.microsoft.com/downloads/details.aspx?FamilyID=b3611543-58b5-4ccc-b6ce-677ebb2a520d), a joint white paper with Juniper discussing IPv6 deployment and benefits. All of these and more are available from http://www.microsoft.com/ipv6. In short, we are working with lots of industry partners to simplify IPv6 deployment and make sure that all of our customers can gain the maximum value from IPv6.
Source of Information : Microsoft Press Windows Server 2008 Networking and Network Access Protection NAP
DHCP Messages
DHCP clients and DHCP servers communicate by exchanging DHCP messages. There are eight types of DHCP messages, all of which are sent as User Datagram Protocol (UDP) messages. DHCP clients in the process of obtaining an IP address configuration use broadcast DHCP messages, sent to the limited broadcast IP address 255.255.255.255. DHCP clients with an IP address and a valid lease use unicast DHCP messages. DHCP clients listen on UDP port 68. DHCP servers and DHCP relay agents listen on UDP port 67.
The eight DHCP message types are the following:
• DHCPDISCOVER Sent by a DHCP client to locate a DHCP server.
• DHCPOFFER Sent by a DHCP server to a DHCP client in response to the DHCPDISCOVER message, containing an offered IP address and other configuration settings.
• DHCPREQUEST Sent by the DHCP client to DHCP servers to request an offered IP address and other configuration settings from a specified DHCP server while implicitly declining offers from other servers, or to confirm the validity of previously allocated addresses (for example, after a restart or to extend an existing DHCP lease).
• DHCPACK Sent by a DHCP server to a DHCP client in response to a DHCPREQUEST message to confirm an IP address and provide the client with those configuration parameters that the client has requested and the server has been configured to provide.
• DHCPNAK Sent by a DHCP server to a DHCP client denying the clients DHCPREQUEST. This might occur if the requested address is incorrect because the client has moved to a new subnet or because the DHCP client’s lease has expired and cannot be renewed.
• DHCPDECLINE Sent by a DHCP client to a DHCP server, informing the server that the offered IP address is unusable because it is in use by another computer.
• DHCPRELEASE Sent by a DHCP client to a DHCP server, relinquishing an IP address and canceling the remaining lease.
• DHCPINFORM Sent from a DHCP client to a DHCP server, requesting additional configuration settings; the client already has a configured IP address. This message type is also used for rogue DHCP server detection in Windows Server 2008.
DHCP messages, options, and protocol operation are defined in RFCs 2131 and 2132.
The eight DHCP message types are the following:
• DHCPDISCOVER Sent by a DHCP client to locate a DHCP server.
• DHCPOFFER Sent by a DHCP server to a DHCP client in response to the DHCPDISCOVER message, containing an offered IP address and other configuration settings.
• DHCPREQUEST Sent by the DHCP client to DHCP servers to request an offered IP address and other configuration settings from a specified DHCP server while implicitly declining offers from other servers, or to confirm the validity of previously allocated addresses (for example, after a restart or to extend an existing DHCP lease).
• DHCPACK Sent by a DHCP server to a DHCP client in response to a DHCPREQUEST message to confirm an IP address and provide the client with those configuration parameters that the client has requested and the server has been configured to provide.
• DHCPNAK Sent by a DHCP server to a DHCP client denying the clients DHCPREQUEST. This might occur if the requested address is incorrect because the client has moved to a new subnet or because the DHCP client’s lease has expired and cannot be renewed.
• DHCPDECLINE Sent by a DHCP client to a DHCP server, informing the server that the offered IP address is unusable because it is in use by another computer.
• DHCPRELEASE Sent by a DHCP client to a DHCP server, relinquishing an IP address and canceling the remaining lease.
• DHCPINFORM Sent from a DHCP client to a DHCP server, requesting additional configuration settings; the client already has a configured IP address. This message type is also used for rogue DHCP server detection in Windows Server 2008.
DHCP messages, options, and protocol operation are defined in RFCs 2131 and 2132.
Source of Information : Microsoft Press Windows Server 2008 TCP IP Protocols and Services
The Disadvantages of IPv4
On today’s Internet, IPv4 has the following disadvantages:
• Limited address space. The most visible and urgent problem with using IPv4 on the modern Internet is the rapid depletion of public addresses. Due to the initial address class allocation practices of the early Internet, public IPv4 addresses are becoming scarce. Organizations in the United States hold most public IPv4 address space worldwide. This limited address space has forced the wide deployment of network address translators (NATs), which can share one public IPv4 address among several privately addressed computers. NATs have the side effect of acting as a barrier for server, listener, and peer-to-peer applications running on computers that are located behind the NAT.
Although there are workarounds for NAT issues, they only add complexity to what should be an end-to-end addressable global network.
• Flat routing infrastructure. In the early Internet, address prefixes were not allocated to create a summarizable, hierarchical routing infrastructure. Instead, individual address prefixes were assigned and each address prefix became a new route in the routing tables of the Internet backbone routers. Today’s Internet is a mixture of flat and hierarchical routing, but there are still more than 85,000 routes in the routing tables of Internet backbone routers.
• Configuration. IPv4 must be configured, either manually or through the Dynamic Host Configuration Protocol (DHCP). DHCP allows IPv4 configuration administration to scale to large networks, but you must also configure and manage a DHCP infrastructure.
• Security. Security for IPv4 is specified by the use of Internet Protocol security (IPsec). However, IPsec is optional for IPv4 implementations. Because an application cannot rely on IPsec being present to secure traffic, an application might resort to other security standards or a proprietary security scheme. The need for built-in security is even more important today, when we face an increasingly hostile environment on the Internet.
• Prioritized delivery. Prioritized packet delivery, such as special handling parameters for low delay and low variance in delay for voice or video traffic, is possible with IPv4. However, it relies on a new interpretation of the IPv4 Type Of Service (TOS) field, which is not supported for all the devices on the network. Additionally, identification of the packet flow must be done using an upper layer protocol identifier such as a TCP or User Datagram Protocol (UDP) port. This additional processing of the packet by intermediate routers makes forwarding less efficient.
• Mobility. Mobility is a new requirement for Internet-connected devices, in which a node can change its address as it changes its physical attachment to the Internet and still maintain existing connections. Although there is a specification for IPv4 mobility, due to a lack of infrastructure, communications with an IPv4 mobile node are inefficient.
All of these issues and others prompted the Internet Engineering Task Force (IETF) to begin the development of a replacement protocol for IPv4 that would solve the problems of IPv4 and be extensible to solve additional problems in the future. The replacement for IPv4 is IPv6.
IPv6 solves the problems of IPv4 in the following ways:
• Huge address space. IPv6 addresses are 128 bits long, creating an address space with 3.4 × 1038 possible addresses. This is plenty of address space for the foreseeable future and allows all manner of devices to connect to the Internet without the use of NATs. Address space can also be allocated internationally in a more equitable manner.
• Hierarchical routing infrastructure. IPv6 addresses that are reachable on the IPv6 portion of the Internet, known as global addresses, have enough address space for the hierarchy of Internet service providers (ISPs) that typically exist between an organization or home and the backbone of the Internet. Global addresses are designed to be summarizable and hierarchical, resulting in relatively few routing entries in the routing tables of Internet backbone routers.
• Automatic configuration. IPv6 hosts can automatically configure their own IPv6 addresses and other configuration parameters, even in the absence of an address configuration infrastructure such as DHCP.
• Required support for IPsec headers. Unlike IPv4, IPv6 support for IPsec protocol headers is required. Applications can always rely on industry standard security services for data sent and received. However, the requirement to process IPsec headers does not make IPv6 inherently more secure. IPv6 packets are not required to be protected with Authentication Header (AH) or Encapsulating Security Payload (ESP).
• Better support for prioritized delivery. IPv6 has an equivalent to the IPv4 TOS field that has a single interpretation for nonstandard delivery. Additionally, a Flow Label field in the IPv6 header indicates the packet flow, making the determination of forwarding for nondefault delivery services more efficient at intermediate routers.
• Support for mobility. Rather than attempting to add mobility to an established protocol with an established infrastructure (as with IPv4), IPv6 can support mobility more efficiently.
Source of Information : Microsoft Press Windows Server 2008 TCP IP Protocols and Services
• Limited address space. The most visible and urgent problem with using IPv4 on the modern Internet is the rapid depletion of public addresses. Due to the initial address class allocation practices of the early Internet, public IPv4 addresses are becoming scarce. Organizations in the United States hold most public IPv4 address space worldwide. This limited address space has forced the wide deployment of network address translators (NATs), which can share one public IPv4 address among several privately addressed computers. NATs have the side effect of acting as a barrier for server, listener, and peer-to-peer applications running on computers that are located behind the NAT.
Although there are workarounds for NAT issues, they only add complexity to what should be an end-to-end addressable global network.
• Flat routing infrastructure. In the early Internet, address prefixes were not allocated to create a summarizable, hierarchical routing infrastructure. Instead, individual address prefixes were assigned and each address prefix became a new route in the routing tables of the Internet backbone routers. Today’s Internet is a mixture of flat and hierarchical routing, but there are still more than 85,000 routes in the routing tables of Internet backbone routers.
• Configuration. IPv4 must be configured, either manually or through the Dynamic Host Configuration Protocol (DHCP). DHCP allows IPv4 configuration administration to scale to large networks, but you must also configure and manage a DHCP infrastructure.
• Security. Security for IPv4 is specified by the use of Internet Protocol security (IPsec). However, IPsec is optional for IPv4 implementations. Because an application cannot rely on IPsec being present to secure traffic, an application might resort to other security standards or a proprietary security scheme. The need for built-in security is even more important today, when we face an increasingly hostile environment on the Internet.
• Prioritized delivery. Prioritized packet delivery, such as special handling parameters for low delay and low variance in delay for voice or video traffic, is possible with IPv4. However, it relies on a new interpretation of the IPv4 Type Of Service (TOS) field, which is not supported for all the devices on the network. Additionally, identification of the packet flow must be done using an upper layer protocol identifier such as a TCP or User Datagram Protocol (UDP) port. This additional processing of the packet by intermediate routers makes forwarding less efficient.
• Mobility. Mobility is a new requirement for Internet-connected devices, in which a node can change its address as it changes its physical attachment to the Internet and still maintain existing connections. Although there is a specification for IPv4 mobility, due to a lack of infrastructure, communications with an IPv4 mobile node are inefficient.
All of these issues and others prompted the Internet Engineering Task Force (IETF) to begin the development of a replacement protocol for IPv4 that would solve the problems of IPv4 and be extensible to solve additional problems in the future. The replacement for IPv4 is IPv6.
IPv6 solves the problems of IPv4 in the following ways:
• Huge address space. IPv6 addresses are 128 bits long, creating an address space with 3.4 × 1038 possible addresses. This is plenty of address space for the foreseeable future and allows all manner of devices to connect to the Internet without the use of NATs. Address space can also be allocated internationally in a more equitable manner.
• Hierarchical routing infrastructure. IPv6 addresses that are reachable on the IPv6 portion of the Internet, known as global addresses, have enough address space for the hierarchy of Internet service providers (ISPs) that typically exist between an organization or home and the backbone of the Internet. Global addresses are designed to be summarizable and hierarchical, resulting in relatively few routing entries in the routing tables of Internet backbone routers.
• Automatic configuration. IPv6 hosts can automatically configure their own IPv6 addresses and other configuration parameters, even in the absence of an address configuration infrastructure such as DHCP.
• Required support for IPsec headers. Unlike IPv4, IPv6 support for IPsec protocol headers is required. Applications can always rely on industry standard security services for data sent and received. However, the requirement to process IPsec headers does not make IPv6 inherently more secure. IPv6 packets are not required to be protected with Authentication Header (AH) or Encapsulating Security Payload (ESP).
• Better support for prioritized delivery. IPv6 has an equivalent to the IPv4 TOS field that has a single interpretation for nonstandard delivery. Additionally, a Flow Label field in the IPv6 header indicates the packet flow, making the determination of forwarding for nondefault delivery services more efficient at intermediate routers.
• Support for mobility. Rather than attempting to add mobility to an established protocol with an established infrastructure (as with IPv4), IPv6 can support mobility more efficiently.
Source of Information : Microsoft Press Windows Server 2008 TCP IP Protocols and Services
User Datagram Protocol (UDP)
UDP, defined in RFC 768, has the following characteristics:
• Connectionless Nodes send UDP messages, consisting of a UDP header and a message, without having to negotiate a connection between communicating peers.
• Unreliable Nodes send UDP messages as datagrams without sequencing or acknowledgment. The Application Layer protocol must reorder and recover lost messages. Typical UDP-based Application Layer protocols either provide their own reliable service or retransmit UDP messages periodically or after a defined time-out value.
• Provides identification of Application Layer protocols UDP provides a mechanism to send messages to a specific Application Layer protocol or process on an internetwork host. The UDP header provides both source and destination process identification.
• Provides checksum of UDP message The UDP header provides a 16-bit checksum of the entire UDP message. UDP is a direct reflection of the datagram services of IP, except that UDP provides a method to pass data to an Application Layer protocol. UDP does not provide the following delivery services:
• Buffering UDP does not provide any buffering of incoming or outgoing data. The Application Layer protocol must provide all buffering.
• Segmentation UDP does not provide any segmentation of large blocks of data. Therefore, the application must send data in small enough blocks so that the IP datagrams for the UDP messages are no larger than the Maximum Transmission Unit (MTU) of the interface on which they are sent. Otherwise, IP on the sending host fragments the UDP message.
• Flow control UDP does not provide any sender-side or receiver-side flow control. UDP message senders can react to the receipt of an Internet Control Message Protocol (ICMP) Source Quench message, but it is not required.
Uses for UDP
Although UDP does not provide any services beyond Application Layer protocol identification and a checksum, there are uses for sending data using UDP, including the following:
• Lightweight protocol To conserve memory and processor resources, some Application
Layer protocols require the use of a lightweight protocol that performs a specific function using a simple exchange of messages. A good example is Domain Name System
(DNS) name queries. Typically, a DNS client sends a DNS Name Query Request message to a DNS server. The DNS server responds with a DNS Name Query Response message. If the DNS server does not respond, the DNS client retransmits the DNS Name Query Request message. If all the DNS clients used TCP rather than UDP, all DNS name queries would be sent reliably, but the DNS server would have to support hundreds or, on the Internet, thousands of TCP connections. The low-overhead solution of using UDP is the best choice for simple request-reply-based Application Layer protocols.
• Reliability provided by the Application Layer protocol If the Application Layer protocol provides its own reliable data delivery services, there is no need for the Transport Layer protocol to provide them. Examples of reliable Application Layer protocols are Trivial File Transfer Protocol (TFTP) and Network File System (NFS).
• Reliability not required due to periodic advertisement process If the Application Layer protocol periodically advertises information, reliable delivery is not required. If an advertisement is lost, it is announced again at the period interval. An example of an Application Layer protocol that uses periodic advertisements is the Routing Information Protocol (RIP).
• One-to-many delivery UDP can be used as the Transport Layer protocol whenever Application Layer data must be sent to multiple destinations using an IP multicast or broadcast address. TCP can be used only for one-to-one delivery. For example, a host sends a broadcast NetBIOS Name Query Request message using UDP.
Source of Information : Microsoft Press Windows Server 2008 TCP IP Protocols and Services
• Connectionless Nodes send UDP messages, consisting of a UDP header and a message, without having to negotiate a connection between communicating peers.
• Unreliable Nodes send UDP messages as datagrams without sequencing or acknowledgment. The Application Layer protocol must reorder and recover lost messages. Typical UDP-based Application Layer protocols either provide their own reliable service or retransmit UDP messages periodically or after a defined time-out value.
• Provides identification of Application Layer protocols UDP provides a mechanism to send messages to a specific Application Layer protocol or process on an internetwork host. The UDP header provides both source and destination process identification.
• Provides checksum of UDP message The UDP header provides a 16-bit checksum of the entire UDP message. UDP is a direct reflection of the datagram services of IP, except that UDP provides a method to pass data to an Application Layer protocol. UDP does not provide the following delivery services:
• Buffering UDP does not provide any buffering of incoming or outgoing data. The Application Layer protocol must provide all buffering.
• Segmentation UDP does not provide any segmentation of large blocks of data. Therefore, the application must send data in small enough blocks so that the IP datagrams for the UDP messages are no larger than the Maximum Transmission Unit (MTU) of the interface on which they are sent. Otherwise, IP on the sending host fragments the UDP message.
• Flow control UDP does not provide any sender-side or receiver-side flow control. UDP message senders can react to the receipt of an Internet Control Message Protocol (ICMP) Source Quench message, but it is not required.
Uses for UDP
Although UDP does not provide any services beyond Application Layer protocol identification and a checksum, there are uses for sending data using UDP, including the following:
• Lightweight protocol To conserve memory and processor resources, some Application
Layer protocols require the use of a lightweight protocol that performs a specific function using a simple exchange of messages. A good example is Domain Name System
(DNS) name queries. Typically, a DNS client sends a DNS Name Query Request message to a DNS server. The DNS server responds with a DNS Name Query Response message. If the DNS server does not respond, the DNS client retransmits the DNS Name Query Request message. If all the DNS clients used TCP rather than UDP, all DNS name queries would be sent reliably, but the DNS server would have to support hundreds or, on the Internet, thousands of TCP connections. The low-overhead solution of using UDP is the best choice for simple request-reply-based Application Layer protocols.
• Reliability provided by the Application Layer protocol If the Application Layer protocol provides its own reliable data delivery services, there is no need for the Transport Layer protocol to provide them. Examples of reliable Application Layer protocols are Trivial File Transfer Protocol (TFTP) and Network File System (NFS).
• Reliability not required due to periodic advertisement process If the Application Layer protocol periodically advertises information, reliable delivery is not required. If an advertisement is lost, it is announced again at the period interval. An example of an Application Layer protocol that uses periodic advertisements is the Routing Information Protocol (RIP).
• One-to-many delivery UDP can be used as the Transport Layer protocol whenever Application Layer data must be sent to multiple destinations using an IP multicast or broadcast address. TCP can be used only for one-to-one delivery. For example, a host sends a broadcast NetBIOS Name Query Request message using UDP.
Source of Information : Microsoft Press Windows Server 2008 TCP IP Protocols and Services
Commonly used TCP/IP ports
When your web browser or email program connects to another computer on the Internet, it does so through a TCP/IP port. If you have a web server or FTP server running on your PC, it opens a port through which other computers can connect to those services. Port numbers are used to distinguish one network service from another.
Mostly, this is done behind the scenes. However, knowing which programs use a specific port number becomes important when you starting considering security. A firewall uses ports to form its rules about which types of network traffic to allow, and which to prohibit. And the Active Connections utility (netstat.exe), used to determine which ports are currently in use, allows you to uncover vulnerabilities in your system using ports. Ports, firewalls, and the Active Connections utility are all discussed in Chapter 7.
Some firewalls make a distinction between TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) ports, which is typically unnecessary. In most cases, programs that use the more common TCP protocol will use the same port numbers as their counterparts that use the less reliable UDP protocol.
Ports are divided into three ranges:
Well-known ports: 0–1023
Registered ports: 1024–49151
Dynamic and/or private ports: 49152–65535
The below lists are most commonly used ports. For a more complete listing, see any of these resources:
http://www.iana.org/assignments/port-numbers
http://www.faqs.org/rfcs/rfc1700.html
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
Those ports marked with an ✗ in are commonly exploited by worms and other types of remote attacks. Unless you specifically need them, you should block them in your firewall or router.
20–21 FTP (File Transfer Protocol)
22 SSH (Secure Shell)
23 Telnet
25 SMTP (Simple Mail Transfer Protocol), used for sending email
42 WINS (Windows Internet Name Service)
43 WhoIs
50–51 IPSec (PPTP Passthrough for VPN, Virtual Private Networking)
53 DNS (Domain Name Server), used for looking up domain names
67 DHCP (Dynamic Host Configuration Protocol)
69 ✗ TFTP
70 Gopher
79 Finger
80 HTTP (Hyper Text Transfer Protocol), used by web browsers to download standard web pages
110 POP3 (Post Office Protocol, version 3), used for retrieving email
119 NNTP (Network News Transfer Protocol), used for newsgroups
123 NTP (Network Time Protocol), used for Windows’ Internet Time feature
135 ✗ RPC (Microsoft Windows Remote Procedure Call)
137–139 ✗ NETBIOS Services
143 IMAP4 (Internet Mail Access Protocol version 4)
161–162 SNMP (Simple Network Management Protocol)
194 IRC (Internet Relay Chat)
220 IMAP3 (Internet Mail Access Protocol version 3)
443 HTTPS (HTTP over TLS/SSL), used by web browsers to download secure web pages
445 ✗ Active Directory, file sharing for Microsoft Windows networks (445 UDP used for SMB/Samba)
500 IPSec (PPTP Passthrough for VPN, Virtual Private Networking)
514 RSH (Remote Shell)
531 AOL Instant Messenger (AIM)
554 RTSP (Real Time Streaming Protocol), used for streaming audio and video
563 NNTPS (Network News Transfer Protocol over SSL), used for secure newsgroups
593 ✗ RPC (Microsoft Windows Remote Procedure Call) over HTTP
691 Microsoft Exchange Routing
750 Kerberos IV email authenticating agent
989–990 FTP over SSL (secure File Transfer Protocol)
992 Telnet over SSL (secure Telnet)
993 IMAP4 over SSL (secure Internet Mail Access Protocol version 4)
995 POP3 over SSL (secure Post Office Protocol, version 3)
1026 ✗ Windows Messenger - pop ups (spam)
1194 OpenVPN
1214 ✗ Kazaa peer-to-peer file sharing
1270 Microsoft Operations Manager 2005 agent (MOM 2005)
1352 Lotus Notes/Domino mail routing
1433–1434 Microsoft SQL database system, monitor
1503 Windows Messenger - application sharing and whiteboard
1512 WINS (Windows Internet Name Service)
1701 VPN (Virtual Private Networking) over L2TP
1723 VPN (Virtual Private Networking) over PPTP
1755 MMS (Microsoft Media Services) for Windows Media Player
1812–1813 RADIUS authentication protocol
1863 Windows Live Messenger - instant messenging
1900 Microsoft SSDP Enables discovery of UPnP devices
3074 Xbox Live (Microsoft gaming console)
3306 MySQL database
3389 Remote Desktop Sharing (Microsoft Terminal Services), used for remote control
4444 ✗ W32.BLASTER.WORM virus
5004 and up Windows Messenger - audio and video conferencing (port is chosen dynamically)
5010 Yahoo! Messenger
5190 AOL Instant Messenger
5631, 5632 pcAnywhere, used for remote control
5800, 5801
5900, 5901
VNC (Virtual Network Computing), used for remote control
6699 Peer-to-peer file sharing, used by Napster-like programs
6891–6901 Windows Live Messenger - file transfer, voice
6881–6999 BitTorrent peer-to-peer file transfer clients
Source of Information : OReilly Windows Vista Annoyances Tips Secrets and Hacks
Mostly, this is done behind the scenes. However, knowing which programs use a specific port number becomes important when you starting considering security. A firewall uses ports to form its rules about which types of network traffic to allow, and which to prohibit. And the Active Connections utility (netstat.exe), used to determine which ports are currently in use, allows you to uncover vulnerabilities in your system using ports. Ports, firewalls, and the Active Connections utility are all discussed in Chapter 7.
Some firewalls make a distinction between TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) ports, which is typically unnecessary. In most cases, programs that use the more common TCP protocol will use the same port numbers as their counterparts that use the less reliable UDP protocol.
Ports are divided into three ranges:
Well-known ports: 0–1023
Registered ports: 1024–49151
Dynamic and/or private ports: 49152–65535
The below lists are most commonly used ports. For a more complete listing, see any of these resources:
http://www.iana.org/assignments/port-numbers
http://www.faqs.org/rfcs/rfc1700.html
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
Those ports marked with an ✗ in are commonly exploited by worms and other types of remote attacks. Unless you specifically need them, you should block them in your firewall or router.
20–21 FTP (File Transfer Protocol)
22 SSH (Secure Shell)
23 Telnet
25 SMTP (Simple Mail Transfer Protocol), used for sending email
42 WINS (Windows Internet Name Service)
43 WhoIs
50–51 IPSec (PPTP Passthrough for VPN, Virtual Private Networking)
53 DNS (Domain Name Server), used for looking up domain names
67 DHCP (Dynamic Host Configuration Protocol)
69 ✗ TFTP
70 Gopher
79 Finger
80 HTTP (Hyper Text Transfer Protocol), used by web browsers to download standard web pages
110 POP3 (Post Office Protocol, version 3), used for retrieving email
119 NNTP (Network News Transfer Protocol), used for newsgroups
123 NTP (Network Time Protocol), used for Windows’ Internet Time feature
135 ✗ RPC (Microsoft Windows Remote Procedure Call)
137–139 ✗ NETBIOS Services
143 IMAP4 (Internet Mail Access Protocol version 4)
161–162 SNMP (Simple Network Management Protocol)
194 IRC (Internet Relay Chat)
220 IMAP3 (Internet Mail Access Protocol version 3)
443 HTTPS (HTTP over TLS/SSL), used by web browsers to download secure web pages
445 ✗ Active Directory, file sharing for Microsoft Windows networks (445 UDP used for SMB/Samba)
500 IPSec (PPTP Passthrough for VPN, Virtual Private Networking)
514 RSH (Remote Shell)
531 AOL Instant Messenger (AIM)
554 RTSP (Real Time Streaming Protocol), used for streaming audio and video
563 NNTPS (Network News Transfer Protocol over SSL), used for secure newsgroups
593 ✗ RPC (Microsoft Windows Remote Procedure Call) over HTTP
691 Microsoft Exchange Routing
750 Kerberos IV email authenticating agent
989–990 FTP over SSL (secure File Transfer Protocol)
992 Telnet over SSL (secure Telnet)
993 IMAP4 over SSL (secure Internet Mail Access Protocol version 4)
995 POP3 over SSL (secure Post Office Protocol, version 3)
1026 ✗ Windows Messenger - pop ups (spam)
1194 OpenVPN
1214 ✗ Kazaa peer-to-peer file sharing
1270 Microsoft Operations Manager 2005 agent (MOM 2005)
1352 Lotus Notes/Domino mail routing
1433–1434 Microsoft SQL database system, monitor
1503 Windows Messenger - application sharing and whiteboard
1512 WINS (Windows Internet Name Service)
1701 VPN (Virtual Private Networking) over L2TP
1723 VPN (Virtual Private Networking) over PPTP
1755 MMS (Microsoft Media Services) for Windows Media Player
1812–1813 RADIUS authentication protocol
1863 Windows Live Messenger - instant messenging
1900 Microsoft SSDP Enables discovery of UPnP devices
3074 Xbox Live (Microsoft gaming console)
3306 MySQL database
3389 Remote Desktop Sharing (Microsoft Terminal Services), used for remote control
4444 ✗ W32.BLASTER.WORM virus
5004 and up Windows Messenger - audio and video conferencing (port is chosen dynamically)
5010 Yahoo! Messenger
5190 AOL Instant Messenger
5631, 5632 pcAnywhere, used for remote control
5800, 5801
5900, 5901
VNC (Virtual Network Computing), used for remote control
6699 Peer-to-peer file sharing, used by Napster-like programs
6891–6901 Windows Live Messenger - file transfer, voice
6881–6999 BitTorrent peer-to-peer file transfer clients
Source of Information : OReilly Windows Vista Annoyances Tips Secrets and Hacks
IPv6 Stack
Basic IPv6 Stack Support
The IPv6 protocol for Windows Server 2008 and Windows Vista supports Internet Engineering Task Force (IETF) standards for IPv6 protocol stack functionality, including the following:
• The IPv6 header (RFC 2460)
• Unicast, multicast, and anycast addressing (RFC 4291)
• The Internet Control Message Protocol for IPv6 (ICMPv6) (RFC 4443)
• Neighbor Discovery (ND) (RFC 4861)
• Multicast Listener Discovery (MLD) (RFC 2710) and MLD version 2 (MLD v2)
(RFC 3810)
• Stateless address autoconfiguration (RFC 4862)
IPv6 Stack Enhancements
The IPv6 protocol for Windows Server 2008 and Windows Vista also supports the following enhancements:
• Dead gateway detection through neighbor unreachability detection Dead gateway detection automatically switches the currently used default router to the next one in a configured list when the current default router becomes unavailable, as detected through neighbor unreachability detection.
• Explicit Congestion Notification support (RFC 3168) When a TCP segment is lost, TCP assumes that the segment was lost due to congestion at a router and performs congestion control, which dramatically lowers the TCP sender’s transmission rate. With Explicit Congestion Notification (ECN) support on both TCP peers and in the routing infrastructure, routers experiencing congestion mark the packets as they forward them. TCP peers receiving marked packets lower their transmission rate to ease congestion and prevent segment losses. Detecting congestion before packet losses are incurred increases the overall throughput between TCP peers. Windows Server 2008 and Windows Vista support ECN, but it is disabled by default. You can enable ECN support with the netsh interface tcp set global ecncapability=enabled command.
• Default route preferences and Route Information options in router advertisements (RFC 4191) With default router preferences, you can configure the advertising routers on a subnet to indicate a preference level so that hosts use the most preferred router as their default router. With Route Information options in router advertisements, routers that do not advertise themselves as default routers can advertise directly attached routes to hosts.
• Strong host model for both sending and receiving The strong host model requires that unicast traffic sent or received must be associated with the network interface on which the traffic is sent or received. For sent traffic, IPv6 can send packets on an interface only if the interface is assigned the source IPv6 address of the packet being sent. For received traffic, IPv6 can receive packets on an interface only if the interface is assigned the destination IPv6 address of the packet being received.
Source of Information : Microsoft Press Understanding IPv6 2nd Edition
The IPv6 protocol for Windows Server 2008 and Windows Vista supports Internet Engineering Task Force (IETF) standards for IPv6 protocol stack functionality, including the following:
• The IPv6 header (RFC 2460)
• Unicast, multicast, and anycast addressing (RFC 4291)
• The Internet Control Message Protocol for IPv6 (ICMPv6) (RFC 4443)
• Neighbor Discovery (ND) (RFC 4861)
• Multicast Listener Discovery (MLD) (RFC 2710) and MLD version 2 (MLD v2)
(RFC 3810)
• Stateless address autoconfiguration (RFC 4862)
IPv6 Stack Enhancements
The IPv6 protocol for Windows Server 2008 and Windows Vista also supports the following enhancements:
• Dead gateway detection through neighbor unreachability detection Dead gateway detection automatically switches the currently used default router to the next one in a configured list when the current default router becomes unavailable, as detected through neighbor unreachability detection.
• Explicit Congestion Notification support (RFC 3168) When a TCP segment is lost, TCP assumes that the segment was lost due to congestion at a router and performs congestion control, which dramatically lowers the TCP sender’s transmission rate. With Explicit Congestion Notification (ECN) support on both TCP peers and in the routing infrastructure, routers experiencing congestion mark the packets as they forward them. TCP peers receiving marked packets lower their transmission rate to ease congestion and prevent segment losses. Detecting congestion before packet losses are incurred increases the overall throughput between TCP peers. Windows Server 2008 and Windows Vista support ECN, but it is disabled by default. You can enable ECN support with the netsh interface tcp set global ecncapability=enabled command.
• Default route preferences and Route Information options in router advertisements (RFC 4191) With default router preferences, you can configure the advertising routers on a subnet to indicate a preference level so that hosts use the most preferred router as their default router. With Route Information options in router advertisements, routers that do not advertise themselves as default routers can advertise directly attached routes to hosts.
• Strong host model for both sending and receiving The strong host model requires that unicast traffic sent or received must be associated with the network interface on which the traffic is sent or received. For sent traffic, IPv6 can send packets on an interface only if the interface is assigned the source IPv6 address of the packet being sent. For received traffic, IPv6 can receive packets on an interface only if the interface is assigned the destination IPv6 address of the packet being received.
Source of Information : Microsoft Press Understanding IPv6 2nd Edition
Architecture of the IPv6 Protocol for Windows Server 2008 and Windows Vista
For Windows Server 2008 and Windows Vista, the TCP/IP protocol stack is a dual IP layer implementation, where only a single implementation of the Transport Layer protocols Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) operate over both Internet layer protocols: Internet Protocol version 4 (IPv4) and Internet Protocol version 6 (IPv6).
The TCP/IP driver file, Tcpip.sys, contains both IPv4 and IPv6 Internet layers. Tcpip6.sys operates between Windows Sockets and the Network Device Interface Specification (NDIS) layers in the Windows network architecture. The architecture of Tcpip.sys consists of the following layers:
• Transport layer Contains the implementations of TCP and UDP.
• Network layer Contains implementations of both IPv4 and IPv6.
• Framing layer Contains modules that frame IPv4 or IPv6 packets. Modules exist for
IEEE 802.3 (Ethernet), IEEE 802.11, and Point-to-Point Protocol (PPP) links. Modules also exist for logical interfaces such as the loopback interface and IPv4-based tunnels. IPv4-based tunnels are commonly used for IPv6 transition technologies. The IPv4 Internet layer appears as the Internet Protocol Version 4 (TCP/IPv4) component in the list of protocols from the properties of a local area network (LAN) connection in the Network Connections folder. The IPv6 Internet layer appears as the Internet Protocol Version 6 (TCP/IPv6) component. You can enable or disable these components per connection in the Network Connections folder, but you cannot uninstall them. You can uninstall the IPv4 Internet layer with the netsh interface ipv4 uninstall command, but you cannot uninstall the IPv6 Internet layer.
Source of Information : Microsoft Press Understanding IPv6 2nd Edition
The TCP/IP driver file, Tcpip.sys, contains both IPv4 and IPv6 Internet layers. Tcpip6.sys operates between Windows Sockets and the Network Device Interface Specification (NDIS) layers in the Windows network architecture. The architecture of Tcpip.sys consists of the following layers:
• Transport layer Contains the implementations of TCP and UDP.
• Network layer Contains implementations of both IPv4 and IPv6.
• Framing layer Contains modules that frame IPv4 or IPv6 packets. Modules exist for
IEEE 802.3 (Ethernet), IEEE 802.11, and Point-to-Point Protocol (PPP) links. Modules also exist for logical interfaces such as the loopback interface and IPv4-based tunnels. IPv4-based tunnels are commonly used for IPv6 transition technologies. The IPv4 Internet layer appears as the Internet Protocol Version 4 (TCP/IPv4) component in the list of protocols from the properties of a local area network (LAN) connection in the Network Connections folder. The IPv6 Internet layer appears as the Internet Protocol Version 6 (TCP/IPv6) component. You can enable or disable these components per connection in the Network Connections folder, but you cannot uninstall them. You can uninstall the IPv4 Internet layer with the netsh interface ipv4 uninstall command, but you cannot uninstall the IPv6 Internet layer.
Source of Information : Microsoft Press Understanding IPv6 2nd Edition
IPv6 troubleshooting - Netsh
The netsh interface ipv6 command context contains many commands that are useful for analyzing the current IPv6 configuration and troubleshooting problems. The most useful commands are:
• netsh interface ipv6 show global. Displays general IPv6 settings, including the default hop limit. Though you rarely need to modify these settings, you can use the netsh interface ipv6 set global command to change them.
• netsh interface ipv6 show addresses. Displays all IPv6 addresses in a much more compact format than ipconfig /all.
• netsh interface ipv6 show dnsservers. Displays all DNS servers that have been configured for IPv6. This does not display any DNS servers that might be configured with IPv4 addresses.
• netsh interface ipv6 show potentialrouters. Displays all advertising IPv6 routers that have been detected on the local network.
• netsh interface ipv6 show route. Lists the automatically and manually configured routes, including tunneling routes.
• netsh interface ipv6 show tcpstats. Lists various IPv6 TCP statistics, including the current number of connections, the total number of both incoming and outgoing connections, and the number of communication errors.
• netsh interface ipv6 show udpstats. Lists various IPv6 UDP statistics, including the number of UDP datagrams that have been sent or received and the number of datagrams that resulted in an error.
• netsh interface ipv6 show neighbors. Displays all cached IPv6 neighbors. To flush the neighbor cache, run the command netsh interface ipv6 delete neighbors.
• netsh interface ipv6 show destinationcache. Displays all cached IPv6 hosts that the computer has communicated with. To flush the destination cache, run the command netsh interface ipv6 delete destinationcache.
When troubleshooting IPv6 transition technologies, you can use the following commands:
• netsh interface ipv6 show teredo. Displays the Teredo configuration, including the Teredo server name and the client port number. You can use the netsh interface ipv6 set teredo command to change these configuration settings.
• netsh interface ipv6 6to4 show command. By using one of the four commands in this context (interface, relay, routing, and state), you can examine the current 6to4 configuration.
• netsh interface isatap show command. By using one of the two commands in this context (router and state), you can examine the current ISATAP configuration.
Source of Information : Microsoft Press Windows Server 2008 Networking and Network Access Protection NAP
• netsh interface ipv6 show global. Displays general IPv6 settings, including the default hop limit. Though you rarely need to modify these settings, you can use the netsh interface ipv6 set global command to change them.
• netsh interface ipv6 show addresses. Displays all IPv6 addresses in a much more compact format than ipconfig /all.
• netsh interface ipv6 show dnsservers. Displays all DNS servers that have been configured for IPv6. This does not display any DNS servers that might be configured with IPv4 addresses.
• netsh interface ipv6 show potentialrouters. Displays all advertising IPv6 routers that have been detected on the local network.
• netsh interface ipv6 show route. Lists the automatically and manually configured routes, including tunneling routes.
• netsh interface ipv6 show tcpstats. Lists various IPv6 TCP statistics, including the current number of connections, the total number of both incoming and outgoing connections, and the number of communication errors.
• netsh interface ipv6 show udpstats. Lists various IPv6 UDP statistics, including the number of UDP datagrams that have been sent or received and the number of datagrams that resulted in an error.
• netsh interface ipv6 show neighbors. Displays all cached IPv6 neighbors. To flush the neighbor cache, run the command netsh interface ipv6 delete neighbors.
• netsh interface ipv6 show destinationcache. Displays all cached IPv6 hosts that the computer has communicated with. To flush the destination cache, run the command netsh interface ipv6 delete destinationcache.
When troubleshooting IPv6 transition technologies, you can use the following commands:
• netsh interface ipv6 show teredo. Displays the Teredo configuration, including the Teredo server name and the client port number. You can use the netsh interface ipv6 set teredo command to change these configuration settings.
• netsh interface ipv6 6to4 show command. By using one of the four commands in this context (interface, relay, routing, and state), you can examine the current 6to4 configuration.
• netsh interface isatap show command. By using one of the two commands in this context (router and state), you can examine the current ISATAP configuration.
Source of Information : Microsoft Press Windows Server 2008 Networking and Network Access Protection NAP
IPv6 Terminology
IPv6 common terms and concepts are defined as follows:
• Node Any device that runs an implementation of IPv6. This includes routers and hosts.
• Router A node that can forward IPv6 packets not explicitly addressed to itself. On an IPv6 network, a router also typically advertises its presence and host configuration information.
• Host A node that cannot forward IPv6 packets not explicitly addressed to itself (a nonrouter). A host is typically the source and a destination of IPv6 traffic, and it silently discards traffic received that is not explicitly addressed to itself.
• Upper-layer protocol A protocol above IPv6 that uses IPv6 as its transport. Examples include Internet layer protocols such as ICMPv6 and Transport layer protocols such as TCP and UDP (but not Application layer protocols such as FTP and DNS, which use TCP and UDP as their transport).
• Link The set of network interfaces that are bounded by routers and that use the same 64-bit IPv6 unicast address prefix. Other terms for “link” are subnet and network segment. Many link-layer technologies are already defined for IPv6, including typical LAN technologies (such as Ethernet and Institute of Electrical and Electronics Engineers [IEEE] 802.11 wireless) and wide area network (WAN) technologies (such as the Point-to-Point Protocol [PPP] and Frame Relay). Additionally, IPv6 packets can be sent over logical links representing an IPv4 or IPv6 network, by encapsulating the IPv6 packet within an IPv4 or IPv6 header.
• Network Two or more subnets connected by routers. Another term for network is internetwork.
• Neighbors Nodes connected to the same link. Neighbors in IPv6 have special significance because of IPv6 Neighbor Discovery, which has facilities to resolve neighbor linklayer addresses and detect and monitor neighbor reachability.
• Interface The representation of a physical or logical attachment of a node to a link. An example of a physical interface is a network adapter. An example of a logical interface is a “tunnel” interface that is used to send IPv6 packets across an IPv4 network by encapsulating the IPv6 packet inside an IPv4 header.
• Address An identifier that can be used as the source or destination of IPv6 packets that is assigned at the IPv6 layer to an interface or set of interfaces.
• Packet The protocol data unit (PDU) that exists at the IPv6 layer and is composed of an IPv6 header and payload.
• Link MTU The maximum transmission unit (MTU)—the number of bytes in the largest IPv6 packet—that can be sent on a link. Because the maximum frame size includes the link-layer medium headers and trailers, the link MTU is not the same as the maximum frame size of the link. The link MTU is the same as the maximum payload size of the link-layer technology. For example, for Ethernet using Ethernet II encapsulation, the maximum Ethernet frame payload size is 1500 bytes. Therefore, the link MTU is 1500. For a link with multiple link-layer technologies (for example, a bridged link), the link MTU is the smallest link MTU of all the link-layer technologies present on the link.
• Path MTU The maximum-sized IPv6 packet that can be sent without performing host fragmentation between a source and destination over a path in an IPv6 network. The path MTU is typically the smallest link MTU of all the links in the path.
A site is an autonomously operating IP-based network that is connected to the IPv6 Internet. Network architects and administrators within the site determine the addressing plan and routing policy for the organization network. An organization can have multiple sites. The actual connection to the IPv6 Internet can be either of the following types:
• Direct The connection to the IPv6 Internet uses a wide area network link (such as Frame Relay or T-Carrier) and connects to an IPv6-capable.
• Tunneled The connection to the IPv6 Internet uses an IPv6 over IPv4 tunnel and connects to an IPv6 tunneling router.
Source of Information : Microsoft Press Understanding IPv6 2nd Edition
• Node Any device that runs an implementation of IPv6. This includes routers and hosts.
• Router A node that can forward IPv6 packets not explicitly addressed to itself. On an IPv6 network, a router also typically advertises its presence and host configuration information.
• Host A node that cannot forward IPv6 packets not explicitly addressed to itself (a nonrouter). A host is typically the source and a destination of IPv6 traffic, and it silently discards traffic received that is not explicitly addressed to itself.
• Upper-layer protocol A protocol above IPv6 that uses IPv6 as its transport. Examples include Internet layer protocols such as ICMPv6 and Transport layer protocols such as TCP and UDP (but not Application layer protocols such as FTP and DNS, which use TCP and UDP as their transport).
• Link The set of network interfaces that are bounded by routers and that use the same 64-bit IPv6 unicast address prefix. Other terms for “link” are subnet and network segment. Many link-layer technologies are already defined for IPv6, including typical LAN technologies (such as Ethernet and Institute of Electrical and Electronics Engineers [IEEE] 802.11 wireless) and wide area network (WAN) technologies (such as the Point-to-Point Protocol [PPP] and Frame Relay). Additionally, IPv6 packets can be sent over logical links representing an IPv4 or IPv6 network, by encapsulating the IPv6 packet within an IPv4 or IPv6 header.
• Network Two or more subnets connected by routers. Another term for network is internetwork.
• Neighbors Nodes connected to the same link. Neighbors in IPv6 have special significance because of IPv6 Neighbor Discovery, which has facilities to resolve neighbor linklayer addresses and detect and monitor neighbor reachability.
• Interface The representation of a physical or logical attachment of a node to a link. An example of a physical interface is a network adapter. An example of a logical interface is a “tunnel” interface that is used to send IPv6 packets across an IPv4 network by encapsulating the IPv6 packet inside an IPv4 header.
• Address An identifier that can be used as the source or destination of IPv6 packets that is assigned at the IPv6 layer to an interface or set of interfaces.
• Packet The protocol data unit (PDU) that exists at the IPv6 layer and is composed of an IPv6 header and payload.
• Link MTU The maximum transmission unit (MTU)—the number of bytes in the largest IPv6 packet—that can be sent on a link. Because the maximum frame size includes the link-layer medium headers and trailers, the link MTU is not the same as the maximum frame size of the link. The link MTU is the same as the maximum payload size of the link-layer technology. For example, for Ethernet using Ethernet II encapsulation, the maximum Ethernet frame payload size is 1500 bytes. Therefore, the link MTU is 1500. For a link with multiple link-layer technologies (for example, a bridged link), the link MTU is the smallest link MTU of all the link-layer technologies present on the link.
• Path MTU The maximum-sized IPv6 packet that can be sent without performing host fragmentation between a source and destination over a path in an IPv6 network. The path MTU is typically the smallest link MTU of all the links in the path.
A site is an autonomously operating IP-based network that is connected to the IPv6 Internet. Network architects and administrators within the site determine the addressing plan and routing policy for the organization network. An organization can have multiple sites. The actual connection to the IPv6 Internet can be either of the following types:
• Direct The connection to the IPv6 Internet uses a wide area network link (such as Frame Relay or T-Carrier) and connects to an IPv6-capable.
• Tunneled The connection to the IPv6 Internet uses an IPv6 over IPv4 tunnel and connects to an IPv6 tunneling router.
Source of Information : Microsoft Press Understanding IPv6 2nd Edition
Frequency versus Wavelength
Frequency and wavelength are inseparably related to each other. As frequency increases, wavelength decreases and vice versa.
• Frequency: The rate at which a radio signal oscillates from positive to negative.
• Wavelength: The length of a complete cycle of the radio signal oscillation.
Wavelength is, of course, a length measurement, usually represented in metric (meters, centimeters, and so on). And frequency is a count of the number of waves occurring during a set time, usually per second. Cycles per second is represented as Hertz (Hz). The dimensions are important to note, because the physical properties of the wave define antenna, cable, and power requirements. Wavelength is critical for antenna design and selection.
Wi-Fi signals operating at a frequency of 2.4 GHz have an average wavelength of about 12 cm. Since the wavelength is so short, antennas can be physically very small. A common design for antennas is to make them 1/4 of a wavelength or less in length, which is barely more than an inch long. That’s why Wi-Fi antennas can perform so well even though they are physically very small. As a comparison, a car radio antenna is much longer to get a decent signal because FM radio signals are an average of 10 feet long.
Wavelength and antenna length go together. To oversimplify, the longer the antenna, the more of the signal it can grab out of the air. Also, antenna length should be in whole, halves, quarters, eighths, and so on of the intended wavelength for best signal reception. The highest reception qualities come from a full wavelength antenna.
Perform this simple math formula to find wavelength: 300 / frequency in megahertz. The answer will be the wavelength in meters. So, 300 / 2437 _ 0.12 meters or 12 cm.
• Frequency: The rate at which a radio signal oscillates from positive to negative.
• Wavelength: The length of a complete cycle of the radio signal oscillation.
Wavelength is, of course, a length measurement, usually represented in metric (meters, centimeters, and so on). And frequency is a count of the number of waves occurring during a set time, usually per second. Cycles per second is represented as Hertz (Hz). The dimensions are important to note, because the physical properties of the wave define antenna, cable, and power requirements. Wavelength is critical for antenna design and selection.
Wi-Fi signals operating at a frequency of 2.4 GHz have an average wavelength of about 12 cm. Since the wavelength is so short, antennas can be physically very small. A common design for antennas is to make them 1/4 of a wavelength or less in length, which is barely more than an inch long. That’s why Wi-Fi antennas can perform so well even though they are physically very small. As a comparison, a car radio antenna is much longer to get a decent signal because FM radio signals are an average of 10 feet long.
Wavelength and antenna length go together. To oversimplify, the longer the antenna, the more of the signal it can grab out of the air. Also, antenna length should be in whole, halves, quarters, eighths, and so on of the intended wavelength for best signal reception. The highest reception qualities come from a full wavelength antenna.
Perform this simple math formula to find wavelength: 300 / frequency in megahertz. The answer will be the wavelength in meters. So, 300 / 2437 _ 0.12 meters or 12 cm.
About Wi-Fi
Wireless networking is accomplished by sending a signal from one computer to another over radio waves. The most common form of wireless computing today uses the IEEE 802.11b standard. This popular standard, also called Wi-Fi or Wireless Fidelity, is now supported directly by newer laptops and PDAs, and most computer accessory manufacturers. It’s so popular that “big box” electronics chain stores carry widely used wireless hardware and networking products.
The IEEE 802.11b Wi-Fi standard supports a maximum speed of 11 megabits per second (Mbps). The true throughput is actually something more like 6 Mbps, and can drop to less than 3 Mbps with encryption enabled. Newer standards like 802.11a and the increasingly popular 802.11g support higher speeds up to 54 Mbps. So why is 802.11b so popular? Because it was first and it was cheap. Even 3 Mbps is still much faster than you normally need to use the Internet.
The 802.11a standard, which operates in the 5 GHz frequency band, is much faster than
802.11b, but never caught on, partly because of the high cost initially and partly because of the actual throughput in the real-world conditions of a deployed wireless network.
The fast and inexpensive 802.11g standard (which uses the same 2.4 GHz band as 802.11b) is rapidly moving to unseat 802.11b from the top of the heap. The very cool thing about “g” is the built-in backwards compatibility with 802.11b. That means any “b” product can connect to a “g” access point. This compatibility makes 802.11g an easy upgrade without tossing out your old client hardware.
Because of the compatibility with 802.11b and 802.11g, there is no great hurry to push the myriad of funky wireless products to the new “g” standard. Most manufacturers have support for basic wireless infrastructure using 802.11b and 802.11g with access points and client adapter. Wi-Fi 802.11b really shines when you look at the host of wireless products available. Not only are there the basic wireless networking devices, like adapters, base stations, and bridges, there are also new products that were unthinkable a few years ago.Wireless disk drive arrays, presentation gateways, audiovisual media adapters, printer adapters,Wi-Fi cameras, hotspot controllers, and wireless broadband and video phones dominate the consumer arena. And the enterprise market is not far behind.
Wi-Fi is the root of a logo and branding program created by the Wi-Fi Alliance. A product that uses the Wi-Fi logo has been certified by the Wi-Fi Alliance to fulfill certain guidelines for interoperability. Logo certification programs like this one are created and promoted to assure users that products will work together in the marketplace. So, if you buy a Proxim wireless client adapter with the Wi-Fi logo branding, and a Linksys access point with the same logo on the product, they should work together.
A megabit is one million binary digits (bits) of data. Network speed is almost always measured in bits per second (bps). It takes 8 bits to make a byte. Bytes are used mostly to measure file size (as in files on a hard disk). A megabyte is about 8 million bits of data. Don’t confuse the term megabyte for megabit or you will come out 8 million bits ahead.
Source of Information : Wi-Fi Toys - 15 Cool Wireless Projects For Home, Office, And Entertainment
The IEEE 802.11b Wi-Fi standard supports a maximum speed of 11 megabits per second (Mbps). The true throughput is actually something more like 6 Mbps, and can drop to less than 3 Mbps with encryption enabled. Newer standards like 802.11a and the increasingly popular 802.11g support higher speeds up to 54 Mbps. So why is 802.11b so popular? Because it was first and it was cheap. Even 3 Mbps is still much faster than you normally need to use the Internet.
The 802.11a standard, which operates in the 5 GHz frequency band, is much faster than
802.11b, but never caught on, partly because of the high cost initially and partly because of the actual throughput in the real-world conditions of a deployed wireless network.
The fast and inexpensive 802.11g standard (which uses the same 2.4 GHz band as 802.11b) is rapidly moving to unseat 802.11b from the top of the heap. The very cool thing about “g” is the built-in backwards compatibility with 802.11b. That means any “b” product can connect to a “g” access point. This compatibility makes 802.11g an easy upgrade without tossing out your old client hardware.
Because of the compatibility with 802.11b and 802.11g, there is no great hurry to push the myriad of funky wireless products to the new “g” standard. Most manufacturers have support for basic wireless infrastructure using 802.11b and 802.11g with access points and client adapter. Wi-Fi 802.11b really shines when you look at the host of wireless products available. Not only are there the basic wireless networking devices, like adapters, base stations, and bridges, there are also new products that were unthinkable a few years ago.Wireless disk drive arrays, presentation gateways, audiovisual media adapters, printer adapters,Wi-Fi cameras, hotspot controllers, and wireless broadband and video phones dominate the consumer arena. And the enterprise market is not far behind.
Wi-Fi is the root of a logo and branding program created by the Wi-Fi Alliance. A product that uses the Wi-Fi logo has been certified by the Wi-Fi Alliance to fulfill certain guidelines for interoperability. Logo certification programs like this one are created and promoted to assure users that products will work together in the marketplace. So, if you buy a Proxim wireless client adapter with the Wi-Fi logo branding, and a Linksys access point with the same logo on the product, they should work together.
A megabit is one million binary digits (bits) of data. Network speed is almost always measured in bits per second (bps). It takes 8 bits to make a byte. Bytes are used mostly to measure file size (as in files on a hard disk). A megabyte is about 8 million bits of data. Don’t confuse the term megabyte for megabit or you will come out 8 million bits ahead.
Source of Information : Wi-Fi Toys - 15 Cool Wireless Projects For Home, Office, And Entertainment
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