Re: What does "Neighbour table overflow" message indicate?

From: Riley Williams (rhw@MemAlpha.CX)
Date: Sun Jul 29 2001 - 00:41:49 EST

Hi Steve.

> I just got this sequence of messages in my system log:
> Jul 28 19:47:44 sunburn kernel: Neighbour table overflow.
> Jul 28 19:47:44 sunburn last message repeated 9 times
> Jul 28 19:47:49 sunburn kernel: NET: 53 messages suppressed.
> Jul 28 19:47:49 sunburn kernel: Neighbour table overflow.
> Jul 28 19:48:07 sunburn kernel: NET: 21 messages suppressed.
> Jul 28 19:48:07 sunburn kernel: Neighbour table overflow.
> Jul 28 19:48:09 sunburn last message repeated 3 times
> Jul 28 19:48:14 sunburn kernel: NET: 4 messages suppressed.
> Jul 28 19:48:14 sunburn kernel: Neighbour table overflow.
> This is on a RedHat v7.1 + SMP kernel v2.4.7 system. What is
> the kernel trying to tell me here?
> Please cc me as I am not a subscriber to this list.

This could be on completely the wrong track, but here's one of the
entries from the 2.4.5 kernel's file (I don't yet have
2.4.7 on my system):

 Q> ARP daemon support (EXPERIMENTAL)
 Q> Normally, the kernel maintains an internal cache which maps IP
 Q> addresses to hardware addresses on the local network, so that
 Q> Ethernet/Token Ring/ etc. frames are sent to the proper address
 Q> on the physical networking layer. For small networks having a
 Q> few hundred directly connected hosts or less, keeping this
 Q> address resolution (ARP) cache inside the kernel works well.
 Q> However, maintaining an internal ARP cache does not work well
 Q> for very large switched networks, and will use a lot of kernel
 Q> memory if TCP/IP connections are made to many machines on the
 Q> network.
 Q> If you say Y here, the kernel's internal ARP cache will never
 Q> grow to more than 256 entries (the oldest entries are expired
 Q> in a LIFO manner) and communication will be attempted with the
 Q> user space ARP daemon arpd. Arpd then answers the address
 Q> resolution request either from its own cache or by asking the
 Q> net.
 Q> This code is experimental and also obsolete. If you want to
 Q> use it, you need to find a version of the daemon arpd on the
 Q> net somewhere, and you should also say Y to "Kernel/User
 Q> network link driver", below. If unsure, say N.

The text in there looks suspiciously related to your problem to me.

Best wishes from Riley.

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