From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ashwanth Goli Subject: Re: ip6-in-ip{4,6} ipsec tunnel issues with 1280 MTU Date: Fri, 27 Apr 2018 21:14:17 +0530 Message-ID: <36807b4bda59b9145a69cc949facbb2b@codeaurora.org> References: <1524743477.2658.38.camel@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Cc: Paolo Abeni , netdev@vger.kernel.org, maloney@google.com, edumazet@google.com, netdev-owner@vger.kernel.org To: David Ahern Return-path: Received: from smtp.codeaurora.org ([198.145.29.96]:35734 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758392AbeD0PoV (ORCPT ); Fri, 27 Apr 2018 11:44:21 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 2018-04-27 20:18, David Ahern wrote: > On 4/27/18 5:02 AM, Ashwanth Goli wrote: >> On 2018-04-26 17:21, Paolo Abeni wrote: >>> Hi, >>> >>> [fixed CC list] >>> >>> On Wed, 2018-04-25 at 21:43 +0530, Ashwanth Goli wrote: >>>> Hi Pablo, >>> >>> Actually I'm Paolo, but yours is a recurring mistake ;) >>> >>>> I am noticing an issue similar to the one reported by Alexis Perez >>>> [Regression for ip6-in-ip4 IPsec tunnel in 4.14.16] >>>> >>>> In my IPsec setup outer MTU is set to 1280, ip6_setup_cork sees an >>>> MTU >>>> less than IPV6_MIN_MTU because of the tunnel headers. -EINVAL is >>>> being >>>> returned as a result of the MTU check that got added with below >>>> patch. > > If you know you are running ipsec over the link why are you setting the > outer MTU to 1280? RFC 2460 suggests the fragmentation of packets for > links with MTU < 1280 should be done below the IPv6 layer: > > 5. Packet Size Issues > > IPv6 requires that every link in the internet have an MTU of 1280 > octets or greater. On any link that cannot convey a 1280-octet > packet in one piece, link-specific fragmentation and reassembly must > be provided at a layer below IPv6. > > Links that have a configurable MTU (for example, PPP links [RFC- > 1661]) must be configured to have an MTU of at least 1280 octets; it > is recommended that they be configured with an MTU of 1500 octets or > greater, to accommodate possible encapsulations (i.e., tunneling) > without incurring IPv6-layer fragmentation. But is this not breaking point (b) from section 7.1 of RFC2473 since the inner packet can be smaller than 1280. https://tools.ietf.org/html/rfc2473#section-7.1