I noticed the following message in my kernel log.
kernel: neigh: timer & !nud_in_timer
(Might be due to a race condition.)
I'm running a UP Linux version 2.6.22.1-rt9
( http://rt.wiki.kernel.org/index.php )
The following /proc entries might be relevant.
/proc/sys/net/ipv4/conf/all/arp_accept
0
/proc/sys/net/ipv4/conf/all/arp_announce
2
/proc/sys/net/ipv4/conf/all/arp_filter
0
/proc/sys/net/ipv4/conf/all/arp_ignore
1
I also lowered the priority of softirq-timer/0 to 10 which means
it can be interrupted by other IRQ handlers.