Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

We are running several virtual machines using KVM with libvirtd with a routed network (the host systems routes an extra subnet for the virtual machines). Host and Guest OS is Gentoo (host on amd64, guests on x86). The VMs are multi-homed with an internal and external network.

A few weeks ago i started to notice sprodic connection issues to our mailserver: The connection timed out. After a few minutes, the connection worked again. During the outage, the internal network is OK, but no traffic goes through the external network (neither in, nor out).

A tracepath shows as the last hop the host. After it, only stars until the maximum hops (again, in and out).

However, if i run a mtr or something similiar from an external host, the connection always succeeds (but only from this host). Because of this, a suspect an arp issues or something like this. I tried to change the ageing time on the bridge, but without success.

Another interesting thing: Pinging another host on the internet from the virtual machine sometimes shows an icmp redirect warning with the IP of the ISP's gateway.

Until now, i have seen this problem only on this single virtual machine, but the setup is not so different from the others. Any ideas?

Edit: Here is the network layout:

Server network layout

share|improve this question
    
Could you please post your ip configuration in more detail? Network address, network mask, router IP, ISP gateway IP and interface configuration of the host in question, please. –  syneticon-dj Sep 22 '11 at 23:20
add comment

1 Answer

up vote 0 down vote accepted

Ok, i solved the problem: the problems where triggered by the ICMP redirect packets sent by the host system. I suspect a different routing path for the packets sent by the VM and the remote server caused the problem.

After setting sysctl -w net.ipv4.conf.all.send_redirects=0, the host stops sending the ICMP messages, and all connection succeed.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.