On Wed, Nov 18, 2009 at 11:39:24AM -0500, Ken Bass wrote: > I have been trying to figure out why my domU NIC becomes unreachable > (could not even ping) at various times. (Normally when the server was > trying to update clamav from the various busy mirrors at 4am). There > also seemed to be some latency when connecting which I chalked up to it > being a virtual machine. > > When I checked my logs, I found thousands of : > Nov 17 04:07:52 nomad kernel: Neighbour table overflow. > and applications reporting errors such as: > Nov 17 04:08:05 nomad freshclam[4085]: nonblock_connect: connect(): fd=5 > errno=105: No buffer space available > > I am running a routed (not bridged) configuration. > > What I figured out is that each Centos 5.4 domU is maintaining an ARP > table. That table is filling up which causes the network to be > unreachable until entries are purged from the cache. Since this is a > routed configuration, the ARP table should really only consist of two or > three entries, my domU, my dom0, and the gateway. > > It appears the networking-scripts until Centos are ignoring the GATEWAY > entry. I end up with route of: > 169.254.0.0 * 255.255.0.0 U 0 0 0 eth0 > default * 0.0.0.0 U 0 0 0 eth0 > > The default route should be the specific IP address in my > /etc/sysconfig/network file. When I manually add the route, the arp > table issue > is fixed. The network stack no longer trys to query an arp entry for > every IP address. > > I found this bug at Xen which was closed as INVALID saying 'Centos is > broken'. That was from 2006. > http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=596 > > Any ideas on what is broken and what the correct fix is? Right now, I > just added > > /sbin/route add -net 0.0.0.0 netmask 0.0.0.0 gw x.x.x.x > > to my /etc/rc.local which seems like a hack solution. > I usually specify the default gateway in /etc/sysconfig/network-scripts/ifcfg-eth0 and it works just fine. -- Pasi