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Routing DFS Replication traffic to a private network

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Several customers have asked us recently whether DFS Replication traffic can be routed through a private network on multi-homed servers. Although DFS Replication does not provide any configuration options for this, one of our DFS Replication gurus, Richard Chinn, suggests using static IP addresses and some entries in the hosts files to isolate network traffic between pairs of servers.

This will be manageable if the number of computers that are replicating with each other is small, and it will effectively isolate the DFS Replication traffic to the private network.  It will have the side-effect of causing most network traffic between pairs of computers in this configuration to go over the private network, so it’s not a perfect solution.  But if you have minimal traffic between pairs of replicating computers (other than the DFS Replication traffic), then this solution may be viable.  It’ll also work if your primary goal is to just get the replication traffic off of the public network, and get it onto some other network.

This works is because the DFS Replication service is able to resolve its replication partners’ DNS names in the normal fashion, but it will get IP addresses for the private network from the hosts file.  The DFS Replication service will initiate connections with partners over the private network.  For other network connections, for example to domain controllers to poll for DFS Replication configuration data from Active Directory, the DFS Replication service will go over the public interface.

Here is sample procedure to set this up between two computers (M1.contoso.com and M2.contoso.com) connected via a crossed Ethernet cable.  It’s assumed that the computers have a public interface as well.  You can extend the procedure to work if you have multiple computers on a private network.

  1. On M1.contoso.com, set up a static IP for a dedicated NIC (e.g. 192.168.1.10).
  2. On M2.contoso.com, set up a static IP for a dedicated NIC (e.g. 192.168.1.11).
  3. Connect a crossed Ethernet cable to both NICs.
  4. On M1, create an entry for M2.contoso.com in %WinDir%\System32\drivers\etc\hosts specifying the 192.168.1.11 IP address. Note you must use the fully qualified domain name.
  5. On M2, create an entry for M1.contoso.com and 192.168.1.10 using the same procedure.
  6. On both M1 and M2, do the following.
    1. net stop dfsr
    2. ipconfig /flushdns
    3. net start dfsr
  7. Configure replication between M1 and M2 in the normal fashion. Replication traffic will go over the private network.

Once you have made the configuration changes, you should create replication test files and ensure replication is working.  You should also use the Task Manager or Performance Monitor to watch network traffic after adding in a lot of content into your replicated folders.  If all is working correctly, you’ll be able to see heavy network usage on the private interface.  Beware of remote differential compression (RDC) and similarity / cross-file RDC as these may skew your bandwidth usage.

--Richard

 

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