Lost Internet connection in two VMs

mlanner

Active Member
Apr 1, 2009
186
1
38
Berkeley, CA
Hi,

I lost Internet connection in two different VMs, one KVM and one OpenVZ, after an ISP outage. All other VMs appear to work fine. The DNS works in the two affected machines, but I can't ping out to any resource outside my local network. Any ideas would be greatly appreciated.

Thanks in advance!
 

udo

Famous Member
Apr 22, 2009
5,912
174
83
Ahrensburg; Germany
Hi,

I lost Internet connection in two different VMs, one KVM and one OpenVZ, after an ISP outage. All other VMs appear to work fine. The DNS works in the two affected machines, but I can't ping out to any resource outside my local network. Any ideas would be greatly appreciated.

Thanks in advance!
Hi,
something wrong with the routing?
Try to find the issue with tcpdump (first "ip route" and traceroute).

Udo
 

mlanner

Active Member
Apr 1, 2009
186
1
38
Berkeley, CA
Thanks for the quick response Udo. I didn't have traceroute installed on those two machines. Don't ask me why. I should have. In any case, just to test, I changed the IP address of one of the machines. It suddenly worked pinging outside resources. However, still, none of those two particular servers could not be reached from the outside while others could.

I eventually placed a call to my ISP to inquire about the outage and informed them about the strange problem of suddenly not being able to access two of my servers. Guess what? After two minutes on the phone with a tech, as suddenly as the machines became unreachable, it magically started working again. The guy swore he didn't do anything. Yeah, right! I certainly didn't do anything.

Anyway ... Nothing to do with Proxmox, although I first thought it may be.

Thanks again.
 

mlanner

Active Member
Apr 1, 2009
186
1
38
Berkeley, CA
Just in case anyone else ever runs into the same/similar problem I thought I would post the final outcome of the strange behavior I encountered with a few of my VMs not being able to connect to the Internet. As pointed out earlier, despite my first analysis that it must have been Proxmox related, it was absolutely not. It turned out that my ISP's ARP cache had to be expired. It took several hours on the first occasion and wasn't fixed until I called them. Then, later on, I came across the solution more or less by accident a while after the first incident, when I migrated some machines. The VMs simply wouldn't connect to the Internet no matter what I did, while all my other VMs would. A call to my ISP asking them to look into it, and getting a more detailed explanation of what they did (and didn't) do, eventually lead to the conclusion that the ARP cache was manually expired, upon which everything started to work as expected again.

Hope this helps someone in the future.

Go Proxmox!
 

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