During the migration to Hyper-V for the DPM servers I stumble upon a problem, the problem is that the network connection for the guests dies at random. A restart of the guest does not resolve the issue, the only resolution I found so far is to restart the host and that is nothing you want to do!
While watching some hockey (I am a big fan of Hockey! Hejja Luleå!!) I was searching for someone that might have the same issue as I and Lo and Behold I did find something on this topic.
Over at Hyper-V.nu I found a interesting read that led me to the most probable culprit, VMQ, and after I disabled VMQ the backups has been running smoothly. Although it might not be a good workaround it is still a workaround. And Santas Workshop is currently a bit behind when it comes to the backbone infrastructure so we can live with the VMQ's being disabled.
Noteworthy, there is a hotfix available that can help you solve the problem.
Windows Server 2012 R2-based Hyper-V server crashes when network traffic passes through a virtual switch
Also, here is a Wikipedia list over at Microsoft.com that includes some updates that are recommended for Hyper-V 2012 R2