# ping www.google.com.sg connect: No buffer space available
# tail -f /var/log/messages Apr 14 03:02:11 svrXXX kernel: __ratelimit: 195 callbacks suppressed Apr 14 03:02:11 svrXXX kernel: Neighbour table overflow. Apr 14 03:02:12 svrXXX kernel: Neighbour table overflow. Apr 14 03:02:12 svrXXX kernel: Neighbour table overflow. Apr 14 03:02:12 svrXXX kernel: Neighbour table overflow.
First, let's see what values have been set on our system
# cat /proc/sys/net/ipv4/neigh/default/gc_thresh1 128 # cat /proc/sys/net/ipv4/neigh/default/gc_thresh2 512 # cat /proc/sys/net/ipv4/neigh/default/gc_thresh3 1024
# echo 1024 > /proc/sys/net/ipv4/neigh/default/gc_thresh1 # echo 4096 > /proc/sys/net/ipv4/neigh/default/gc_thresh2 # echo 8192 > /proc/sys/net/ipv4/neigh/default/gc_thresh3
# ifdown eth0 # ifup eth0
Do note that these settings are NOT PERSISTENT. To make these settings persistent, please run the following for a RHEL/CENTOS machine
# echo "net.ipv4.neigh.default.gc_thresh1=1024" >> /etc/sysctl.conf # echo "net.ipv4.neigh.default.gc_thresh2=4096" >> /etc/sysctl.conf # echo "net.ipv4.neigh.default.gc_thresh3=8192" >> /etc/sysctl.conf # sysctl -p