RE: Problem with PMTU discovery on ICMP packets

[David S. Miller]

Svenning Soerensen writes:
 > I've done a bit more testing. The behaviour doesn't change across reboots.
 > Instead, it seems to be the case that:
 > If the packet fits within the MTU of the outgoing interface, DF is set.
 > If the packet doesn't fit, and thus gets fragmented, DF is clear on all
 > fragments.
 > Does this make sense?

Yes.  I've put the following patch into my tree.
Thanks for doing the detective work.

--- net/ipv4/icmp.c.~1~	Sun Apr 29 21:40:40 2001
+++ net/ipv4/icmp.c	Wed May  9 18:20:58 2001
@@ -3,7 +3,7 @@
  *	
  *		Alan Cox, <[e-mail]>
  *
- *	Version: $Id: icmp.c,v 1.75 2001/04/30 04:40:40 davem Exp $
+ *	Version: $Id: icmp.c,v 1.76 2001/05/10 01:20:58 davem Exp $
  *
  *	This program is free software; you can redistribute it and/or
  *	modify it under the terms of the GNU General Public License
@@ -1006,6 +1006,7 @@
 	icmp_socket->sk->allocation=GFP_ATOMIC;
 	icmp_socket->sk->sndbuf = SK_WMEM_MAX*2;
 	icmp_socket->sk->protinfo.af_inet.ttl = MAXTTL;
+	icmp_socket->sk->protinfo.af_inet.pmtudisc = IP_PMTUDISC_DONT;
 
 	/* Unhash it so that IP input processing does not even
 	 * see it, we do not wish this socket to see incoming