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Thin Client and Virtual Machines Thread, Hyper-V cluster not updating switch ARP in Technical; I have been stuck with this since last Friday and it's really starting to depress me, as I finally thought ...
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    sonofsanta's Avatar
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    Unhappy Hyper-V cluster not updating switch ARP

    I have been stuck with this since last Friday and it's really starting to depress me, as I finally thought I was ready to push ahead with deploying proper new servers when I noticed this behaviour, and it's a problem that involves a great deal of waiting to see if it's fixed so I am bored of watching it now.

    I'm just testing a new Hyper-V cluster before pushing ahead with production, and when I live migrate my test VM, pings into the server drop for anywhere between 20-100 pings, unless I ping out from the server. So far, so similar to many other issues, and clearly ARP-related - the switch visibly has the incorrect ARP entry until I ping out from the guest.

    I've run Wireshark captures on both Hyper-V hosts in the cluster on the NIC with the virtual network, and captured the debug output from my HP A5800 switch for ARP packets as well, and as best I can tell, the issue is because Hyper-V never sends a gratuitous ARP out to update the routing tables.

    Is there anything likely to be stopping these gratuitous ARP packets being sent out by the server? I can see other gratuitious packets being sent round the network on the Wireshark logs.

    This is all Server 2008R2, hosts and guests, as up to date as can be (apart from this week's patches, not got round to them yet), running a cluster on an FC SAN hosting the CSV, on HP DL380 G7s with a mix of onboard Intel NICs and expansion-card Broadcom NICs. The NICs are teamed but disabling that/changing settings/running on only a single NIC does nothing to resolve the situation. I'm performing the Live Migrations from a third physical server running SCVMM.

    Has anyone got any clues? I've tried destroying and recreating the cluster and it's made no difference; I don't yet want to rebuild the virtual hosts from scratch because that's a fairly time consuming option.

    Help, my sanity is at stake

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    sonofsanta's Avatar
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    It's taken me 6 days, but finally worked it out. Hurrah!

    Turns out the guest VM had an emulated NIC set up. Switching this to the better synthetic NIC meant that the gratuitous ARP packets started being broadcast successfully and I just managed to do a Live Migration without dropping a single ping. A single one! Modern technology is &*%£ing incredible, isn't it?

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    stevenlong1985 (10th May 2012)

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    stevenlong1985's Avatar
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    Dont know what happened to mine today, everything stopped working some how. the 2 physical servers lost connection to the SAN. and now everything is running very slow. I think its a DNS issue. I've reset everything and no luck I getting me really down tonight

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