Re: DF (Don't frag) issues

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 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.

	David.