Re: Routing 600+ vlan's via linux problems (looks like arp problems)

On Fri, May 04, 2007 at 05:48:18AM +0200, Øyvind Vågen Jægtnes wrote:
Hi again :)

On 5/4/07, Willy Tarreau <w@xxxxxx> wrote:
On Thu, May 03, 2007 at 11:12:09PM +0200, Øyvind Vågen Jægtnes wrote:
On 5/3/07, Jan Engelhardt <jengelh@xxxxxxxxxxxxxxx> wrote:

On May 3 2007 22:53, Willy Tarreau wrote:
For the rest all we see in the arp cache is (incomplete)

I suspect that your arp cache is full (128 entries by default).
Check /proc/sys/net/ipv4/neigh/gc_thresh1 (128 for me). You can
set it as high as gc_thresh2 (512 for me), and I don't know what
happens above.

Above, you will perhaps need the not-so-elegant userspace arpd :-/

Yes, i was suspecting that the arp cache got full, but i will try
increasing it :)
Would there be any huge bugs if i change these lines in arp.c:

.gc_thresh1 = 128,
.gc_thresh2 = 512,

to

.gc_thresh1 = 700,
.gc_thresh2 = 700,

under the definition for struct arp_tbl?

I don't think it could cause a problem, but network people will surely
correct me if I'm wrong.

System is up and running perfectly now, it is routing everything at
about 200 mbps now with only 5% load avg with the above changes to
arp.c

So the real question now is, why is this number so low by default?
It would probably be much better if this could be handled dynamically
in the kernel.

I remember I read an argument against this a long time ago, but I
don't remember where. I think it was some arbitrary decision that
people using more than X ARP entries will need arpd. Most probably
the code path in the ARP updates is/was not much optimized to handle
large number of entries. Think about cable operators who may have
10-20000 entries !

Its a Juniper M7i
It comes default with a 5400 rpm laptop 2.5" harddrive but now we
bought a more robust "server" 2.5" harddrive.

The "server" ones are not necessarily more robust, often they are faster.

It still barfs on the OS
install, so the linux is doing all the job now. Will get a juniper guy
to come and fix :)

As a side note, i'm starting to wonder if it was worth the $20k when i
could just have a linux machine to do the job with a clone for backup
;)

That's often how linux penetrates the enterprise ;-)

Willy

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