RE: [SQU] More on WCCP and truncated GRE packets. --HELP

Whoops - I mean MTU.

At 04:14 PM 12/13/00 -0600, you wrote:
>I think this Cisco doc might shed some light on GRE tunneling and the
>truncated 24 bytes...
>
>http://www.cisco.com/warp/public/105/56.html
>
>hope this helps,
>
>-----Original Message-----
>From: Lincoln Dale [mailto:ltd@cisco.com]
>Sent: Wednesday, December 13, 2000 3:56 PM
>To: Nathan Lewis
>Cc: Duane Wessels; squid-users@ircache.net
>Subject: Re: [SQU] More on WCCP and truncated GRE packets. --HELP
>
>
>At 03:34 PM 13/12/2000 -0600, Nathan Lewis wrote:
> >Possibilities:
> >
> >1. I have a very recent version of IOS - perhaps Cisco saw what squid was
> >doing and decided to screw with their packets a little (truncating them by
> >24 bytes most of the time) to break anything besides "authorized"
> >implementations of WCCP. It is their protocol remember....
>
>it is NOT "their" (sic) protocol. the protocol is documented at the ietf
>web-site.
>details of WCCP are public. see
>http://www.cisco.com/warp/public/732/wccp/index.html.
>
> >2. I have a faulty router / some sort of router configuration problem. I
> >will post the entire config if anyone is fluent in IOS and wants to take a
> >look.
>
>send me the output of "sh tech" from your router to me in private email.
>you may be hitting an IOS bug.
>
> >Is there anyone familiar enough with the format of the GRE packet out
> >there that can look at my previous posting of a few of these truncated
> >data packets and figure out what is being left out? Perhaps ip_wccp will
> >need to be modified to unencapsulate those as well (or do truncated
> >packets simply get dropped by the kernel?)
>
>truncated packets may be due to a bug. it may be due to the fact that the
>user is sending a large packet which would exceed the MTU when a GRE header
>is prepended. in this case, the router will fragment the packet.
>
>it may be that ip_wccp cannot handle this [perfectly valid] case. squid
>enforcing a MSS to the client such that no fragmentation could occur may
>help.
>
>
>cheers,
>
>lincoln.
>
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