Re: DF (Don't frag) issues

David Malone wrote:
> 
> On Sat, Apr 23, 2005 at 10:27:53PM +1000, Matthew Sullivan wrote:
> > Ok well thanks to Andrew _at_ Supernews and a lot of debugging it appears
> > there is a bug....
> >
> > sys/netinet/ip_icmp.c: line 440
> >                        if (!mtu)
> >                                mtu = ip_next_mtu(mtu, 1);
> > Problem is ip_next_mtu will always return 0 when called with (0, 1) ...
> 
> I think this might be a bug, but Andre would know better.  Andre -
> it looks to me as if the first argument to ip_next_mtu here should
> be the current MTU for the path, but it is being set to the mtu
> from the ICMP message, which (in this case) is zero.

This is a bug indeed.  Let me think how to fix this most efficiently...

> (This is in the code that has just been moved to tcp_ctlinput.)
> 
> > Apparently the gateway should be suggesting a MTU value for use.... the
> > gateway is also FreeBSD 5.3 so something needs fixing .. :-/
> 
> Are you using ip fast forwarding on the gateway? It calculates the
> size that is put into the ICMP message in a slightly different way
> to the other forwrd path.

The quoted code above is used only for incoming ICMP packets.  It
does not generate them?  What is the problem being observed exactly?

-- 
Andre