[CentOS] Neighbour table overflow.

Wed Mar 12 04:56:22 UTC 2008
Garrick Staples <garrick at usc.edu>

On Wed, Mar 12, 2008 at 10:12:19AM +0530, Indunil Jayasooriya alleged:
> Hi,
> 
> I am getting below error on mailgw. it has 2 ethernets.
> eth0 is connected to internet, while eth1 is connected to LAN where
> there are about 300 PCs.
> 
> 
> 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.
> 
> Mar 12 09:14:20 gateway kernel: NET: 633 messages suppressed.
> Mar 12 09:14:20 gateway kernel: Neighbour table overflow.
> 
> 
> it happens very often. I goolgled and found some info.
> 
> many talk about below file
> 
> /proc/sys/net/ipv4/neigh/default/gc_thresh1
> 
> I increased its value to 300
> 
> But, i still get the same error.

The "default" is only applied to devices as they come up.  You'll need to also
increase the values in the interface-specific directories.

Be sure to also adjust your /etc/sysctl.conf because manually playing in /proc
won't survive a reboot.

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).

-- 
Garrick Staples, GNU/Linux HPCC SysAdmin
University of Southern California

Please avoid sending me Word or PowerPoint attachments.
See http://www.gnu.org/philosophy/no-word-attachments.html
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