There appears to be a pretty serious router bug in kernel 2.6.8. One
reference to it is here:
http://www.debiantalk.com/_Bug279666_kernel-image-2_6_8-1-k7_Runs_out_of_network_buffers-10116882-5788-a.html
and a followup that it may now be fixed in later kernels here:
http://lists.debian.org/debian-kernel/2004/12/msg00233.html.
This is my personal experience with it....
My router fails few days now and when it fails the syslog fills up with
messages saying "kernel: dst cache overflow".
I have done a lot of googling tonight to research this. Apparently this has
happened to other people in the past, but not very often for a long stretch
until recently when I can find mention of this problem once again popping up
again starting around September.
From what I gather this error means that the routing cache filled up. The
maximum size of the routing cache can be set by changing
/proc/sys/net/ipv4/route/max_size. The default on my mandrake install is
32768.
The current size of the routing cache can apparently be determined by "grep
ip_dst_cache /proc/slabinfo". On my router this value is slowly, but
constantly, trending upwards at all times. However, if I list the cache
with "route -Cn", or "cat /proc/net/rt_cache", I see
significantly fewer
entries than what slabinfo reports.
Two things have changed since the time when my router ran smoothly without
any problems:
1) I upgraded from Mandrake 9.2.1 to Mandrake 10.1
2) I now have two WAN connections coming into the router that map to
different halves of the same subnet on my LAN.
I use HTB for bandwidth shaping, and I also map my public IP addresses to
private address space, but this part of my config has not really changed.
At this point I''m just throwing this out as a heads-up At the moment
I''m
just monitoring the ip_dst_cache value from /proc/slabinfo, and when it
starts to get close to the vavlue in /proc/sys/net/ipv4/route/max_size I
just reboot the router... not the most elegant situation, but at least I no
longer have random crashes. I''m going to look into trying a different
kernel in the next day or so to see if that resolves the issue.
Chris
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