Subject: Re: Was change to ip_push_pending_frames intended to break udp
	(more specifically, WCCP?)
From: Vlad Yasevich <vladislav.yasevich@hp.com>
To: Paul P Komkoff Jr <i@stingr.net>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org
In-Reply-To: <20060520140434.2139c31b.akpm@osdl.org>
References: <20060520191153.GV3776@stingr.net>
	 <20060520140434.2139c31b.akpm@osdl.org>
Content-Type: text/plain
Organization: Linux and Open Source Lab
Date: Mon, 22 May 2006 14:22:32 -0400
Message-Id: <1148322152.15322.299.camel@galen.zko.hp.com>
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On Sat, 2006-05-20 at 14:04 -0700, Andrew Morton wrote:
> Paul P Komkoff Jr <i@stingr.net> wrote:
> >
> > Hello!
> > 
> > I have a userspace application, which talks WCCP2 with cisco routers.
> > It sends and receives UDP packets on port 2048. After I've updated my
> > server to 2.6.16, it stopped working.
> > 
> > Examining logs and packet dumps of previous (2.6.15 kernel) vs.
> > current, I found, that cisco will not understand packets generated by
> > 2.6.16. The only difference in that packets was IP id field, which was
> > increasing (1, 2, ...) with old kernel, and always 0 with 2.6.16.
> > 
> > Looking thru the changelog, I've found a suspect. It was this commit:
> > http://kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1a55d57b107c3e06935763905dc0fb235214569d
> > 
> > Reverting this patch fixes my problems - the router understands
> > packets again.
> > 
> > I took a look through the code and ip_select_ident codepath but still
> > don't understand why it setting id to 0.

IP id is set to 0 on unconnected sockets when the DF bit is set (path
mtu discovery is enabled).  Try issuing a connect() in your application
and see if the ids are increasing again.

-vlad

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