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Hyper-V guest machine cannot connect to anything other than the host and another hyper-v server on the same host. Cannot contact gateway

Posted on 2014-10-13
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Last Modified: 2014-11-12
I have 2 hyper V guests on the same host. They are both configured the same in regards to the network cards and both have the same gateway and DNS servers. They are on the same domain, the one that is functioning properly is a domain controller. I have tried removing and reinstalling the NIC on the machine acting up but am not able to get any change in connectivity, I can only contact the host and its contents. I am using Server Standard 2012 R2 for both the host and guest OS's. Any ideas on what I should do other than do a full reload on machine acting up?
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Question by:PIMSupport
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by:Cliff Galiher
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Is the virtual NIC connected to the right virtual switch? The described behavior is indicative of an internal virtual switch instead of an external one.

The other low-hanging fruit possibility is a misconfigured subnet mask, which isn't unique to Hyper-V. Basic networking...to use a gateway, the server has to properly know what traffic is local and what traffic needs to be routed. An ipconfig would be helpful.
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by:PIMSupport
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There is only one switch configured, both hyper-v guests are on that switch and it is an external switch. I double checked the subnet mask and thank god that was not off or that would have been embarassing. ipconfig attached
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by:PIMSupport
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by:Cliff Galiher
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Next steps would be nslookup tests. Traceroute tests. Ping tests. See where things are choking up.
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by:PIMSupport
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Right, I ping tested earlier and  I can ping the host, I can ping the other hyper-v guest, but I cannot ping the gateway or anything outside of the NIC on the host.

Had not tried a tracert, that just comes back with a destination host unreachable.

nslookup is able to bring back results for anything I try because the other guest on the hyper-v host is a domain controller so it is pulling info from that DNS
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by:Cliff Galiher
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Is there another machine on the local network that does respond to ping from the host and the working VM *and* fails to respond to the dysfunctional VM? Both facets are important. After all, a software firewall can block pings, and then it wouldn't respond to working VMs either, so isolating the differences in behavior is important.
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by:PIMSupport
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Yep, I can ping another domain controller on the network from both the host and functional vm. The dysfunctional vm cannot ping it.
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by:PIMSupport
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BTW the firewall on all of these machines is off.
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by:Cliff Galiher
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Very strange. I don't have any easy suggestions I can make at this point.
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by:PIMSupport
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Also, as of right now, because of port space issues, there is only 1 NIC plugged in currently.

That being said, when we remove the virtual switch and create a new one it marries up with the first guest machine that connects to it and allows network access. The second machine that is cut on has these issues where it can't contact the default gateway and acts like it is part of the internal network only. I will be plugging in the second NIC tomorrow to see if that helps...do you think the fact these 2 guests and the host are on the same NIC is causing my issue?
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by:David Johnson, CD, MVP
David Johnson, CD, MVP earned 250 total points
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do you think the fact these 2 guests and the host are on the same NIC is causing my issue?  NO as I have multiple guests on the same nic, many guests use different vlans even.
Check your Virtual Switch settingCheck your Networking Setting -- don't use legacy adapter
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Cliff Galiher earned 250 total points
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No, the way the virtual switch code works, the physical NIC becomes a layer 2 port. All layer 3 stuff happens at the VM level. The only time I've seen issues like you describe is when people have messed with the physical NIC settings after creating the switch (like trying to enable IPv4 again.)  But honestly, at that point, trying to troubleshoot in a forum becomes a fame of 20 questions and still has a very low success rate. I'd either build up a new VM, and if it works, migrate the data. Or call in a hyper-v specialist and pay them. It saves money in the long term.
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by:PIMSupport
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Come to find out the switch that this is plugged into has a port-security set at 3 so I am exceeding that maximum since there is a dummy switch between them funneling them into 1 port. Thanks for the suggestions and help guys. Handing out points for the good suggestions and walkthrough
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