[CentOS-virt] Issues getting Xen NAT networking to work on CentOS 5.3

Andrew Montgomery-Hurrell darkliquid at darkliquid.co.uk
Wed Apr 15 09:54:52 UTC 2009

I've got a virtual network setup going on where I have 3 VMs running
on a host system which ran fine under CentOS 5.2 but under 5.3
everything to do with the networking has gone weird.

I can't seem to access my VMs over the internal virtual network
interfaces, setting their IPs statically in the VM conf files, for
some reason the VIFs end up with an IP 127 higher, ie.
becomes Ignoring that issue, the main one is that that IP,
rather than connect to the running VM's network interface instead just
connects to localhost on the host system. The only way I can access
the VMs is with 'xm console' which obviously isn't very useful
considering I need the VMs to host web content. The VMs can
access the outside world and download things such as updates, etc,
but the host system can't access them (obviously the outside world
can't and this is intentional in this case as their interfaces aren't
exposed externally).

I've tried this with and without the firewall running and the issue
persists, so it's definitely not iptables screwing things up. What's
annoying is that my setup worked perfectly fine in 5.2 but in 5.3 it's
been nothing but hassle to get working and I'm completely stumped with
getting this networking issue sorted.

Anyone have any ideas what might be causing the issue?

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