I was noticing the below error message in /var/log/messages. I also noticed that my linux DHCP server was not serving leases. Again, I modified the sysctl file to fix the issue.
Problem:
Jun 21 07:56:03 localhost kernel: [36050.926734] ipv4: Neighbour table overflow.
Jun 21 07:56:03 localhost kernel: [36050.930354] ipv4: Neighbour table overflow.
Jun 21 08:01:02 localhost kernel: [36349.592127] ipv4: Neighbour table overflow.
Solution:
1. Edit /etc/sysctl.conf
vi /etc/sysctl.conf2. Change to have the following values
net.ipv4.neigh.default.gc_thresh1 = 8192
net.ipv4.neigh.default.gc_thresh2 = 16384
net.ipv4.neigh.default.gc_thresh3 = 16384
2. To load new changes type the following command:
sysctl -p
2. To load new changes type the following command:
sysctl -p
What are these 3 parameters?
These parameters are defined in the Linux Kernel Code in /include/net/neighbour.h as integer, which suggests that maximal accepted value is (2^32 - 1)
gc_thresh1 - The minimum number of entries to keep in the ARP cache.
gc_thresh2 - The soft maximum number of entries to keep in the ARP cache.
gc_thresh3 - The hard maximum number of entries to keep in the ARP cache.
