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Weirdness with Virtual Ethernet Interfaces on Ubuntu

I’ve been doing some experimenting with virtual Ethernet (veth) interfaces in Ubuntu as part of the ongoing work with network namespaces, LXC, and related technologies. A few times I’ve run into a very weird situation, and I have yet to figure out exactly what’s happening. I thought I might share it here in the hopes that someone else has seen this behavior and knows a) what causes it, and b) how to fix it.

I’ll start with a pretty vanilla installation of Ubuntu 12.04 LTS and Open vSwitch (OVS). When I run ip link list, I get output that looks something like this (click the image for a larger version):

Before adding the veth pair

OK, nothing unusual or unexpected there.

Next, I’ll add a pair of veth interfaces:

ip link add vmveth0 type veth peer vmveth1

Then the output of ip link list looks like this (I’ve circled some of the output to draw your attention; again, you can click for a larger version):

After adding the veth pair

See? The name of the veth peer interface gets garbled up and somehow corrupted. Because of this, nothing works—I can’t use the veth pair to connect network namespaces, or to connect a Linux bridge to OVS, or anything else. Rebooting the system does not fix the problem; only a rebuild seems to get rid of it.

Anyone have any ideas?

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