Re: Was change to ip_push_pending_frames intended to break udp (more specifically, WCCP?)

[Vlad Yasevich <vladislav.yasevich@hp.com>]

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