Re: sendmsg() leaves Identification field in IP header empty

Vladimir Ivaschenko (hazard@francoudi.com)
Wed, 5 Dec 2001 22:22:35 +0200


Andi Kleen wrote about "Re: sendmsg() leaves Identification field in IP header empty":

>
> In theory the hack from TCP could be ported to UDP too, but I'm not sure if it is
> worth it for WCCP (to be honest I don't know what WCCP is so I cannot assess if
> it's important enough to add a workaround for it)

Andi, thanks a lot for the insight, I will try your suggestions.
WCCP is a Web Cache Communication Protocol; it is used by Cisco
routers to forward traffic to proxies. What is confusing is that
send() generates an ID for packets with DF set, at least when
used in a way like Squid uses it. I briefly checked Squid source
code and didn't find any places where it would disable MTU Path
discovery.

> > Sorry if I'm wrong but I think this is a kernel problem because
> > sendmsg() is a system call. On RH6.2 with 2.2.19 this doesn't happen,
>
> It's strictly not a bug because the RFCs don't require an IPID for !DF.

Ok, an intercompatibility issue. :-)

-- 
Best Regards
Vladimir Ivaschenko
Certified Linux Engineer (RHCE)
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