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I have two Dell servers running Server 2008 R2 Datacenter Service Pack 1 with Hyper-V. For some reason, these two servers cannot ping each other (nor can the VM's on each respective server ping VM's on the other server).

HOWEVER, every other device on our network can ping those servers and the VM's on them! Note: ALL devices are on the SAME SUBNET!

Essentially there is something not allowing access between those two servers only. It can't be a firewall issue because everything is on the same subnet and other devices can ping those servers.

The two servers are plugged into the same switch and sit right next to each other on the rack.

I ran a network packet trace and when one server tries to ping the other server the ARP request is broadcast, however, the other server does not see the ARP request! There are never any ARP entries (IP-MAC) for those two servers in their respective ARP tables (arp -a). They do have arp entries for all other devices that have communicated with them. Just those two servers can't see each other over Layer 2 (or 3) it seems??

If I also run a packet tracer on a 3rd Vista machine it can see the ARP broadcast when one server tries to ping the other, but the packet trace running on the destination server never shows this arp broadcast thus it never replies with it's MAC address thus the ping just times out. Remember, every other device on my network can ping those two servers. Everything is on the same subnet!

Any suggestions? This is driving me a little crazy! How is this even possible?

Thanks

PS: The closest Issue I can find is this issue here: Windows Server 2008 R2 network adapter stops working, requires hard reboot and the problem ended up being an NT kernel issue with a private patch from Microsoft - could this be the same problem (although it seems permanent for me, whereas the poster in this thread said it happened intermittently). I am running SP1 which was just released a few days ago....

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