Enhancing Replication and WAN Utilization at the Branch Office

Windows Server 2008 R2 introduces new technologies and refines existing ones to maximize performance, replication, and file sharing and to reduce WAN bandwidth utilization consumed between branch offices and hub sites. The following technologies that address and improve bandwidth utilization, latency, and reliability of the WAN links at a branch office include the following:

. Read-Only Domain Controllers
. Next Generation TCP/IP
. Distributed File System
. DirectAccess
. Virtualization
. Group Policy
. SMB v2


Read-Only Domain Controllers
As revealed earlier in this chapter, the amount of information replicated over the WAN between a Read-Only Domain Controller residing at a branch office and a writable domain controller at a hub site is significantly minimized. This is because changes do not originate at an RODC, eliminating the need to replicate data from an RODC to a writable domain controller replication partner at a hub site, resulting in a reduction of bandwidth and WAN utilization being used.


Next Generation TCP/IP Stack
A tremendous amount of improvement is seen in the Next Generation TCP/IP stack introduced in Windows Server 2008 R2. Some of the features for the new TCP/IP stack that directly impact and improve branch office WAN utilization and replication include the following:

. Receive Window Auto-Tuning—Support for Receive Window Auto-Tuning is new in the Next Generation TCP/IP stack. Receiver-side throughput is improved through Receive Window Auto-Tuning because this feature is able to calculate the best possible receive window size for each connection by taking into account bandwidth, latency connection, and application retrieval rate. Bandwidth performance naturally improves with better throughput. Bandwidth performance can improve even more if all applications receive TCP data.

. Compound TCP/IP (CTCP)—Compound TCP/IP, which is most often used for TCP connections that have a large receive window size in addition to a large bandwidth delay product, ultimately improves receiver-side throughput. With CTCP, the amount of data sent across connections is significantly greater; however, TCP connections are not impacted negatively. If CTCP and Receive Window Auto-Tuning are used together, even more benefits, including increased link utilization and performance gains for large bandwidth delay connections, can be witnessed.

. ECN support—When a TCP segment is lost, TCP assumes that it was because of congestion at a router, so it performs congestion control. This lowers the TCP sender’s transmission rate. With Explicit Congestion Notification (ECN) 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. This increases the overall throughput between TCP peers.

. Improved routing—Path maximum transmission unit (PMTU) black-hole router detection automatically adjusts the PMTU for a connection when large TCP segments are detected.

. RFC optimizations—The TCP/IP stack has better support for RFCs related to TCP communications.

. Neighbor detection—The Next Generation TCP/IP stack supports neighbor unreachability detection for IPv4 traffic. A computer such as a branch office maintains status about whether neighboring computers such as a hub site are reachable. This provides better error detection and recovery when computers are not available.

. Dead Gateway support—Unlike the previous Windows versions of Dead Gateway Detection, the Next Generation TCP/IP Dead Gateway support now provides a failover and failback mechanism when encountering dead gateways.


Distributed File System (DFS)
DFS in Windows Server 2008 R2 builds upon the completely revised replication engine in Windows Server 2003 R2. DFS, which was first introduced with Windows 2000 Server, provides a robust multimaster file replication service that is significantly more scalable and efficient in synchronizing file servers than its predecessor, File Replication Service (FRS).

With Windows Server 2008 R2, DFS includes an impressive list of benefits for both Active Directory and branch office server management, including simplified branch server management, reduction of backups, and more efficient storage management. In addition, DFS Replication (DFSR) enhances branch office implementations because it is possible to schedule and throttle replication schemes, support multiple replication topologies, and utilize Remote Differential Compression (RDC) to increase WAN efficiency. If WAN connections fail, data can be stored and forwarded until WAN connections become available. As a result, WAN replication is reduced and optimized, branch office mission-critical files can be replicated among branch offices, hub sites can reduce the amount of IT management that takes place in the branch office, and the need for backups can also be reduced.

Additionally, a new feature that was introduced in Windows Server 2008 R2 is support for read-only copies of information stored in Distributed File System (DFS) replicas. Because information that is stored on a read-only DFS replica is read-only, users are not able to modify/delete/create the replicated content. Therefore, information that is stored in a read-only DFS replica is protected at branch office locations from accidental modification.


Group Policies
Windows Server 2008 R2 now uses DFSR to replicate Group Policy Objects between domain controllers within a domain. By leveraging DFSR differential replication, changes only occur between two domain controllers and not all of the domain controllers as in the past. As a result, the amount of bandwidth required during Group Policy replication is greatly reduced.

Group policies, which are the traditional Administrative Template files, are now replaced with new XML-based files called ADMX in Windows Server 2008 R2. Moreover, the new ADMX files are stored in a centralized store within SYSVOL. Thus, the new templates, storage of group policies, and utilization of DFSR for replication improve branch office solutions because less data needs to be replicated between the branch office and hub site.


SMB Version 2.0
Another enhancement for Windows Server 2008 R2 branch office deployments is the server message block (SMB) protocol version 2.0. SMB, originally invented at IBM, is an application-level network file-sharing protocol mainly applied when accessing files, printers, serial ports, and miscellaneous communications between computers on a network.

The protocol hasn’t evolved much since it was originally created 15 years ago. As a result, the protocol is considered to be overly chatty and generates unnecessary network traffic between computers on a network. This especially hinders users at branch office implementations when accessing files over the WAN to a hub site, especially if the WAN link is slow or already congested.

Microsoft understands the concerns and limitations with the existing version of SMB and has completely rewritten SMB to meet the demand of today’s branch office needs. The benefits and improvements of the new SMB version 2.0 protocol on WAN network performance and end-user experience when transferring data between the branch office and hub sites include the following:

. Efficiency, performance, and data streaming are improved and are four to five times faster than the older version of SMB.

. The client can increase parallel requests.

. Offline capabilities are included, which is beneficial on slow networks and improves the end-user experience.

. Synchronization performance for offline files is improved.

. Multiple client requests can be compounded into a single round-trip.

. Users can now work in offline mode and synchronize changes on demand.

. Server scalability has been increased by reduced per-connection resource usage.

. The amount of bandwidth required for network communications has been dramatically reduced.

Source of Information : Sams - Windows Server 2008 R2 Unleashed