From: Benoit PAPILLAULT <benoit.papillault@free.fr>
To: hadi@cyberus.ca
Cc: Andrew Morton <akpm@linux-foundation.org>,
netdev@vger.kernel.org, bugzilla-daemon@bugzilla.kernel.org,
bugme-daemon@bugzilla.kernel.org
Subject: Re: [Bugme-new] [Bug 14837] New: gretap does not fragment IP packets
Date: Mon, 21 Dec 2009 02:17:31 +0100 [thread overview]
Message-ID: <4B2ECCAB.8010702@free.fr> (raw)
In-Reply-To: <1261227303.11973.2.camel@bigi>
jamal a écrit :
> Sending back an ICMP is good behavior. Sending it "who knows" is not ;->
> Make sure it is sent to the originator of the packet. The originator of
> the packet should play nice and reduce the path mtu.
>
> One work around is to reduce the gre device mtu to something less than
> 1500B.
>
> cheers,
> jamal
>
>
>
As I explained in my original message, the gre device MTU must be 1500
bytes (since it is used in an Ethernet bridge). To reproduce the
problem, I did a very simple setup with two machines (A & B) connected
with an Ethernet cable (so no router between them).
On machine A :
# ip link add gre0 type gretap local <A> remote <B>
# ifconfig gre0 mtu 1500
# ifconfig gre0 192.192.192.1 up
On machine B:
# ip link add gre0 type gretap local <B> remote <A>
# ifconfig gre0 mtu 1500
# ifconfig gre0 192.192.192.2 up
On machine A:
# ping 192.192.192.2 => working
# ping -s 1434 192.192.192.2 => working, match a GRE packet of 1500 bytes
# ping -s 1435 192.192.192.2 => not working, match a GRE packet of 1501
bytes (1435+8+20+38)
# ping -s 1472 192.192.192.2 => not working, match an IP packet of 1500
bytes
Doing a tcpdump on the machine (like tcpdump -pni any) shows that ICMP
packets are simply dropped!
Using tracepath 192.192.192.2, a tcpdump -pni lo shows :
IP 192.192.192.1 > 192.192.192.1: ICMP 192.192.192.2 unreachable - need
to frag (mtu 1500), length 556
Regards,
Benoit
next prev parent reply other threads:[~2009-12-21 1:24 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-14837-10286@http.bugzilla.kernel.org/>
2009-12-18 23:32 ` [Bugme-new] [Bug 14837] New: gretap does not fragment IP packets Andrew Morton
2009-12-18 23:47 ` Stephen Hemminger
2009-12-19 12:55 ` jamal
2009-12-21 1:17 ` Benoit PAPILLAULT [this message]
2009-12-21 19:09 ` jamal
2010-01-07 14:30 ` Benoit PAPILLAULT
2010-01-10 16:03 ` jamal
2010-01-10 17:43 ` Benoit PAPILLAULT
2010-01-10 21:59 ` Herbert Xu
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