Re: [squid-users] How does WCCP work ?

From: Joe Cooper <>
Date: Sat, 17 Mar 2001 22:38:04 -0600

Ok...Let's see if the problem can be isolated:

What is your IOS version?

If a version that supports both v1 and v2 of WCCP, have you switched it
to v1?

I know that you are able to load the ip_wccp module, because we've
already discussed that. Have you set up a network dump, using a tool
such as tcpdump or ethereal, between the router and the Squid box to see
if the Squid is actually sending out HERE_I_AM messages?

To answer your questions:

For a complete description of the protocol, here is the specification
for v1:

Short version:

The protocol is pretty simple. Squid sends a packet to the router:
"HERE_I_AM" on the WCCP port (2048), which contains the IP of the
sending cache. The router sends a packet back, with an ID: "I_SEE_YOU".
When the cache replies: "HERE_I_AM" again, it confirms two way
connectivity by including the ID from the previous "I_SEE_YOU".

There is no "WCCP channel", just port 2048, but those packets are not
encapsulated. So, even without the ip_wccp module loaded, I think you
will still be able to 'connect' the cache and the router, and see
HERE_I_AM and I_SEE_YOU packets going back and forth. Redirected
requests, however, will not work until one of the GRE modules is loaded.

If you are not seeing this communication, then either your Squid is
sending the WCCP messages, the messages are not reaching the router, or
the router is ignoring them. You need to do some form of packet dump to
see if those messages are coming and going at all.

Awie wrote:

> Folks,
> I am beginning frustrated because not able to make WCCP running at our
> Squid system.
> My Squid is known by Cisco as CacheEngine. But redirection progress was
> not happen. I did not see "Here_I_AM / I_See_You" signal in my router
> although I am in debug and terminal mode.
> I followed all of FAQ instruction and suggestion from some of you
> (thanks for Joe Cooper, Jan Haluza, etc), PLUS Cisco staff. However, my
> WCCP is still not running.
> Hope someone would explain me how actually Squid communicate with router
> through WCCP channel.
> Please advise.
> Thx & rgds,
> Awie

                      Joe Cooper <>
                  Affordable Web Caching Proxy Appliances
Received on Sat Mar 17 2001 - 21:32:30 MST

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