[CentOS-virt] Xen domU default gateway missing/ARP table full
pasik at iki.fi
Thu Nov 19 12:23:20 UTC 2009
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: 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.
> 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.
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