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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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