Re: [squid-users] Performance tunning !

Henrik Nordström wrote:
> Joe Cooper wrote:
>
>
>> I'll buy that. Though this won't fix things in the case of the MTU
>> problem with WCCP (at least not in my experience). Of course, the
>> MTU only has to be dropped to 1476 (or somewhere around that, I
>> don't recall exactly) in that case, which does no real harm to
>> throughput.
>
>
> Well.. unless I have misunderstood the WCCP MTU problem this is a
> problem of the MTU between the router and the cache, and needs to be
> addressed at the router. Disabling or changing the MTU size on the
> cache server won't help for this. The MTU for the WCCP encapsulation
> in the router needs to be at most the MTU between the router and the
> cache. If your cache is on a directly attached network then I would
> file this into the category IOS bugs.

In the two cases I've seen it, setting a max MTU of 1476(?...1500 minus
whatever the GRE overhead is, which I think is 24 bytes) on the real
interface (i.e. not the gre interface) of the Squid machine makes the
problem disappear. Disabling MTU discovery did not have an impact.

My understanding of this issue is rather vague, but the method for
dealing with it has worked when I've needed it, so I don't spend much
think time on it. ;-)

It is likely that doing the same on the Cisco router side would also
have a similar effect. I've never tried it, so I can't say for sure.

-- 
Joe Cooper <joe@swelltech.com>
Web caching appliances and support.
http://www.swelltech.com