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Address Neighbour Tables

Created by dave. Last edited by dave, 6 years and 48 days ago. Viewed 3,970 times. #3
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Problem

Mar 12 09:14:00 gateway kernel: NET: 697 messages suppressed.
Mar 12 09:14:00 gateway kernel: Neighbour table overflow.
Mar 12 09:14:05 gateway kernel: NET: 660 messages suppressed.
Mar 12 09:14:05 gateway kernel: Neighbour table overflow.
Mar 12 09:14:10 gateway kernel: NET: 682 messages suppressed.
Mar 12 09:14:10 gateway kernel: Neighbour table overflow.
Mar 12 09:14:15 gateway kernel: NET: 700 messages suppressed.
Mar 12 09:14:15 gateway kernel: Neighbour table overflow.

The same problem can sometimes manifest as a No buffer space available error when using ping or arping against many hosts sequentially.

Solution

In my very large flat network, I have the following in /etc/sysctl.conf:
net.ipv4.neigh.default.gc_thresh1 = 4096
net.ipv4.neigh.default.gc_thresh2 = 8192
net.ipv4.neigh.default.gc_thresh3 = 8192
net.ipv4.neigh.default.base_reachable_time = 86400
net.ipv4.neigh.default.gc_stale_time = 86400
These are documented in arp(7).

You can also whack the running values:

# echo 4096 > /proc/sys/net/ipv4/neigh/default/gc_thresh1
# echo 8192 > /proc/sys/net/ipv4/neigh/default/gc_thresh2
# echo 8192 > /proc/sys/net/ipv4/neigh/default/gc_thresh3
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