[CentOS-virt] Xen domU default gateway missing/ARP table full

Thu Nov 19 18:47:33 UTC 2009
Ken Bass <kbass at kenbass.com>

Christopher Hunt wrote:
> Ken,
>      I think Pasi's on to something there, I bet the GATEWAY command 
> in ifcfg-eth0 is mistyped or has a syntax error.  In the interem, 
> however, a better hack might be to move the route statement from 
> rc.local, which only runs at boot, to 
> /etc/sysconfig/network-scripts/route-eth0 .  That will enable the 
> network service to restart or the eth0 interface to downup without 
> removing the default route. 
Thanks for this tip. I removed the GATEWAY and GATEWAYDEV from 
/etc/sysconfig/network which got rid of the initial (incorrect route) 
and added

default via dev eth0 onlink

to the /etc/sysconfig/network-scripts/route-eth0

Note the use of the 'onlink' option. It appears to be working fine 
without the arp traffic.

I guess I thought this was a more common configuration when using Xen in 
a routed configuration. I'm not sure if the network scripts allow a 
mechanism to add the 'onlink' option so that GATEWAY/GATEWAYDEV 
specified are actually used. Grepping through the network-scripts does 
not yield anything.

If other people are using this in the same way I am, you will need to do 
this change or else there will be all the unnecessary arp cache activity 
for every single ip address which might fill up your arp table.