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I have two Windows 2008 Servers. One is a domain controller and the other is a member of the domain.

The domain member machine has 2 NICs, one for internet facing traffic and the other for private domain traffic. This machine has worked for quite some time handing traffic on each NIC correctly until a few weeks ago. (I don't know what has changed, the issue has been escalated to me from support)

All traffic now wants to leave via the internet facing NIC regardless of destination.

If I disable and enable the private NIC, suddenly I can ping the DC and the DC can ping back. Internet traffic works also. This is all fine until I attempt to perform an action such as gpupdate on the member or 'Manage' the domain member from the DC. The traffic will drop suddenly and private traffic tries to exit via the internet facing NIC until I disable and en-enable the private NIC. (this also occurs if I disable the internet facing NIC and try)

Adding static routes and altering metrics appear to have no affect.

Event viewer offers nothing of interest other than timeouts for DNS or DC connection attempts.

What would cause this drop in traffic when I perform anything other than a ping between the two? Thoughts appreciated.

NIC 1 - Private 
No Gateway

NIC 2 - Public

Route Print:

Interface List
 14...02 00 2e 14 72 ad ......Intel(R) PRO/1000 MT Network Connection #2
 13...26 67 81 08 fe 70 ......Intel(R) PRO/1000 MT Network Connection
  1...........................Software Loopback Interface 1

IPv4 Route Table
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
*3     10         On-link*3    266*3         On-link*3    266         On-link*3    266         On-link    306         On-link    306         On-link    306         On-link    266         On-link    266         On-link    266         On-link    306         On-link    266         On-link*3    266         On-link    306         On-link    266         On-link*3    266
Persistent Routes:
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Any errors in the switch where the private NIC is connected? Wonder if the NIC is going down/having negotiation issues. Try a different port, try to set it to 10/100/1000 full-duplex on both NIC and switch port. – gravyface Aug 24 '12 at 11:28
I should add, this is a virtual cloud environment. Both machines are setup on the same VLAN. Recreating the VLAN and reassigning does not resolve it. – Damo Aug 24 '12 at 11:30
That makes it a bit more difficult, but it could very be an issue at a layer that's abstracted from your server. I would contact support, as you're not going to be able to see the big picture from where you're at. – gravyface Aug 24 '12 at 11:33
thanks, time to write a long email I think – Damo Aug 24 '12 at 11:38
Have any virtual server host updates been applied recently? – Ashley Steel Aug 28 '12 at 19:19
up vote 1 down vote accepted

The issue was a bug in the VM Host software. Changing the NIC to another manufacture resolved the issue.

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