Re: [squid-users] yahoo problem

On Saturday 20 April 2002 18:23, Joe Cooper wrote:
>
> Cisco has an article in their archives on the subject, and I've
> seen posts from Lincoln Dale stating that IOS is not flawed in this
> regard. I know enough to fix it, but not enough to judge what part
> of the chain is to blame for the trouble. But it is a well-know
> issue, and occurs with a number of web caches in certain
> environments when using WCCP.
>
> The link at Cisco:
>
> http://www.cisco.com/warp/public/105/56.html

This discusses the general problem of fragmentation of the GRE
tunnel. Indeed a problem. If the GRE tunnel between your Cisco and
the cache server goes over a media with a lower MTU than assigned by
the WCCP Cisco router, causing the GRE packets to get fragmented
somewhere between the WCCP router and the cache then PMTU discovery
will fail for the clients. This problem applies to all forms of
packet level tunneling.

> I think I recall there being an article specifically about this
> problem with WCCP, but I couldn't find it in a search...Maybe I'm
> misremembering.

I don't think WCCP will deal properly with traffic beeing already
fragmented when it hits the WCCP router, but other than that there
should not be any WCCP specific issues in this area.. but I don't
know how to instruct a Cisco WCCP router about the GRE MTU to use for
the tunnel between the router and the cache to avoid the GRE tunnel
fragmentation issue above..

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