From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Fw: [Bug 55861] New: PMTU discovery no longer works in Linux 3.6+ with routers that do not send next hop MTU information Date: Wed, 27 Mar 2013 08:31:27 -0700 Message-ID: <20130327083127.0740d793@nehalam.linuxnetplumber.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit To: netdev@vger.kernel.org Return-path: Received: from mail-pb0-f51.google.com ([209.85.160.51]:60109 "EHLO mail-pb0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752518Ab3C0Pbk (ORCPT ); Wed, 27 Mar 2013 11:31:40 -0400 Received: by mail-pb0-f51.google.com with SMTP id rr4so2633205pbb.38 for ; Wed, 27 Mar 2013 08:31:40 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: Begin forwarded message: Date: Wed, 27 Mar 2013 08:25:40 -0700 From: "bugzilla-daemon@bugzilla.kernel.org" To: "stephen@networkplumber.org" Subject: [Bug 55861] New: PMTU discovery no longer works in Linux 3.6+ with routers that do not send next hop MTU information https://bugzilla.kernel.org/show_bug.cgi?id=55861 Summary: PMTU discovery no longer works in Linux 3.6+ with routers that do not send next hop MTU information Product: Networking Version: 2.5 Kernel Version: 3.6 onwards Platform: All OS/Version: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: IPV4 AssignedTo: shemminger@linux-foundation.org ReportedBy: _@maxb.eu Regression: Yes After upgrading recently, I found that path MTU discovery no longer worked correctly for accessing some devices on the other side of an IPsec tunnel. Bisection revealed the problems started with 3.6 and are still present in 3.9-rc4 (latest available at time of reporting). Some investigation into code changes leads me to the belief that Linux lost support for handling ICMP destination unreachable fragmentation needed packets for which the next hop MTU field is zero. This is an expected condition when dealing with older routers, as RFC792 originally defined ICMP destination unreachable fragmentation needed without a next hop MTU field, and it was later added in bytes previously allocated as unused. The particular router in my case generating such packets is a machine running OpenBSD 4.6. A commit that appears to be of particular interest in this bug is https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=46517008e1168dc926cf2c47d529efc07eca85c0 -- Configure bugmail: https://bugzilla.kernel.org/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug.