NLB and DFS : Duplicates and retransmission errors

I'm using wireshark to sniff traffic on our network and noticed there's a lot of retransmission errors.

It seems DFS replication is causing conflicts with the CAS array. After disable one of the file server momentarily, duplicates and retransmission errors has dropped off completely.

How things are setup are as follows:
* Two CAS servers setup in a CAS array  
* Two file servers with DFS replication

Each time I connect to Exchange using an email, I can see a lot of retransmission/duplication errors. What's really unusual is the source IP address of client computer contains the MAC address of the file server when these errors do occur.

Example of what I mean is as follows:

Duplication/retransmission are always with packets as follows:
Dest IP:, Source IP:, Dest MAC: AA, Source MAC: CC
Dest IP:, Source IP:, Dest MAC: AA, Source MAC: DD

Source MAC is ends up being one of the file servers MAC, even though the source IP belongs to the clients computer. Really, really odd.
Any known problem with having these two services on the same network? Your help is greatly appreciated. Thank you.
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dave558Author Commented:
It appears not to be the DFS services as disabling still results in multiple retransmission and duplicates. Shutting down one of the file server does eliminate a huge proportion of duplicates/retransmissions.

However, I can still see a few duplicate/retransmission due to the same reason as the source MAC containing the file server's MAC instead of the clients.
dave558Author Commented:
It's most likely to be due to switching loops. However, as the environment is virtualised and due to limitations of hyper-v, problem cannot be fixed.

Using solutions capable of STP or restructuring the layout completely are some means of working around this.

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dave558Author Commented:
Answers problem.
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