Unstable connectivity behaviour on Hyper-V guests

Environment:

Windows Server 2008 R2 with Hyper-V Role

Symptopms:

 VMs on a certain Hyper-V host were having bizzare connectivity patterns, when I tried to ping other machines, I would get three types of ICMP reponses for the same ICMP request. below is a snapshot

 

The network configuration is shown below, with the stable and the unstable communication paths

 

 

Resolution:

1- disable netDMA on the Host NIC (check this article http://support.microsoft.com/kb/951037)

2- Disable Large Send Offload on the Host NIC (in the advanced properties of the NIC)

 

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