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I have two VMs that, up until yesterday, have been able to talk to each other just fine. Now they don't. I've been trying to get this fixed for several hours now, but haven't been able to figure anything out.

When I ping server1 from server2, the packets leave server2 but never arrive at server1. When I ping server2 from server1 the packets leave server1, arrive at server2, a reply is sent from server2, and never gets back to server1. That leads me to believe my issue is with server1. This isn't just for ICMP traffic, this is for any type of packet. I've already cleared out the firewalls on both VMs to accept everything, so I don't think its a firewall issue at this point, but some other issue with the way the VM is configured. Traceroutes between the servers get all the way up to the host node before dropping.

I've attached all of my packet captures and tracerts. Does anyone have any suggestions?

UPDATE: I thought I had a solution. I asked the provider of server2 to assign me a new IP, which allowed the two servers to talk again. Now, a day later, I'm having that same problem with a new IP.

Trace Route

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blazerunner44
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2 Answers2

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This sounds like a routing loop. Do your instances happen to have multiple vNICs attached? Also, check you local routing table on each host. You should see something similar to this:

$ route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 0.0.0.0 192.168.1.10 0.0.0.0 UG 0 0 0 eth0

spyderdyne
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  • The coment formating is a little wierd but basically I have one line thats 0.0.0.0 all the way through `root@server1:~# route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 0.0.0.0 0.0.0.0 U 0 0 0 venet0 root@server1:~# ` – blazerunner44 May 19 '16 at 18:13
  • what is the output if ifconfig? I don't see any interfaces in your routing table. What distro is this? – spyderdyne May 19 '16 at 18:16
  • The interface is venet0. I updated the question with an ifconfig. Its running ubuntu – blazerunner44 May 19 '16 at 18:20
  • Make sure each one can ping its gateway and get a response to rule out misconfiguration on your virtual interfaces. Then try a telnet to port 22 across the same connection that you are attempting to ping across. If you can telnet and not ping then your ICMP allow rule might not be correct on one of them. – spyderdyne May 19 '16 at 18:32
  • They are both able to ping their gateways, and they don't have any problems pinging anything else (eg. google.com) just issues pinging each other which makes me think its a firewall type problem. I've cleared out both firewalls to allow everything, but they still don't ping each other. They used to be able to up until a couple days ago. Another thing that's strange is that they are both able to ping each other with IPv6. – blazerunner44 May 19 '16 at 18:39
  • That's strange. My best guess is that one provider or the other is preventing ICMP inbound from the WAN. – spyderdyne May 19 '16 at 18:42
  • It's every type of traffic between the two hosts, TCP, UDP, and ICMP. I am able to connect to both VMs just fine from home, just not from each other. Thanks for the help. – blazerunner44 May 19 '16 at 18:44
  • It sounds like time to open a ticket with the provider that has the instance you cant reach. Sorry I couldn't find the cause for you. – spyderdyne May 19 '16 at 18:46
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Check Any port blocking from Antivirus running on Host machine or VM's,

Also try disabling Antivirus once.

Its Me
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