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SubjectRE: Problem with PMTU discovery on ICMP packets

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, <alan@redhat.com>
*
- * 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
-
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