Re: Last Call: <draft-ietf-6man-rfc1981bis-04.txt> (Path MTU Discovery for IP version 6) to Internet Standard

Joe Touch <touch@isi.edu> Wed, 15 February 2017 21:26 UTC

Return-Path: <touch@isi.edu>
X-Original-To: ipv6@ietfa.amsl.com
Delivered-To: ipv6@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 0DC0D129556; Wed, 15 Feb 2017 13:26:28 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -6.901
X-Spam-Level:
X-Spam-Status: No, score=-6.901 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, RP_MATCHES_RCVD=-0.001] autolearn=ham autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id crYJjuRxfOya; Wed, 15 Feb 2017 13:26:27 -0800 (PST)
Received: from boreas.isi.edu (boreas.isi.edu [128.9.160.161]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 2BCEF129849; Wed, 15 Feb 2017 13:26:27 -0800 (PST)
Received: from [128.9.160.81] (nib.isi.edu [128.9.160.81]) (authenticated bits=0) by boreas.isi.edu (8.13.8/8.13.8) with ESMTP id v1FLP4gL012163 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES128-SHA bits=128 verify=NOT); Wed, 15 Feb 2017 13:25:05 -0800 (PST)
Subject: Re: Last Call: <draft-ietf-6man-rfc1981bis-04.txt> (Path MTU Discovery for IP version 6) to Internet Standard
To: gorry@erg.abdn.ac.uk
References: <148599312602.18643.4886733052828400859.idtracker@ietfa.amsl.com> <1859B1D9-9E42-4D65-98A8-7A326EDDE560@netapp.com> <f8291774-409e-2948-3b29-83dbb09d39d9@si6networks.com> <63eaf82e-b6d5-bff5-4d48-479e80ed4698@gmail.com> <2d36e28c-ee7d-20fc-3fec-54561e520691@si6networks.com> <C0A114C1-5E4A-4B8E-A408-55AF1E30873F@netapp.com> <3A5429F6-0EA6-436A-AF30-E55C9026F456@employees.org> <8cf1fe7d-bdfd-5e81-e61f-55d9ecd5d28a@isi.edu> <7E9AB9E8-3FCB-4475-BEEB-F18CFC4BC752@employees.org> <8076a1ea-182d-9cbe-f954-3e50f0fc53d9@isi.edu> <E11F9A4D-DE9E-4BFD-8D0D-252842719FC5@employees.org> <619f0dc52a514f07a70b44126aeb66f3@XCH15-06-08.nw.nos.boeing.com> <da3de0a5-fe7f-c874-db1d-da2684619213@si6networks.com> <706163b815ef439bbd9e0a17eba83512@XCH15-06-08.nw.nos.boeing.com> <e201c72e-b7c1-5a5f-eacb-93896cd7a7bb@si6networks.com> <58A33D08.4090505@erg.abdn.ac.uk>
From: Joe Touch <touch@isi.edu>
Message-ID: <196e8c39-784a-3a25-b6ab-d7eaa664f0fa@isi.edu>
Date: Wed, 15 Feb 2017 13:25:03 -0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1
MIME-Version: 1.0
In-Reply-To: <58A33D08.4090505@erg.abdn.ac.uk>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
X-ISI-4-43-8-MailScanner: Found to be clean
X-MailScanner-From: touch@isi.edu
Archived-At: <https://mailarchive.ietf.org/arch/msg/ipv6/6m_Y7Br82OcJEwWED4vTVd0OkmE>
Cc: "tsv-area@ietf.org" <tsv-area@ietf.org>, "6man-chairs@ietf.org" <6man-chairs@ietf.org>, 6man WG <ipv6@ietf.org>, "ietf@ietf.org" <ietf@ietf.org>, "draft-ietf-6man-rfc1981bis@ietf.org" <draft-ietf-6man-rfc1981bis@ietf.org>
X-BeenThere: ipv6@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: "IPv6 Maintenance Working Group \(6man\)" <ipv6.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ipv6>, <mailto:ipv6-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ipv6/>
List-Post: <mailto:ipv6@ietf.org>
List-Help: <mailto:ipv6-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ipv6>, <mailto:ipv6-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 15 Feb 2017 21:26:28 -0000

Hi, Gorry (et al.),

On 2/14/2017 9:23 AM, Gorry Fairhurst wrote:
> There is no mention that paths including tunnels can eat ICMPv6 PTB
> messages on the tunnel segment, blackholing them, which prevents
> reaching the destination. 

Nor should there be, IMO.

A tunnel is a link layer to the network whose packets it transits.

ICMPs generated inside a tunnel aren't "eaten", so much as they operate
at a different layer for a different reason (e.g., to tune
ingress-egress source fragmentation of encapsulated packets).

PTB messages inside a tunnel are (IMO) most correctly interpreted by the
ingress (which is an *interface* on a router or host, most correctly
IMO) as changing the MTU of the tunnel as a link. If that MTU change
affects packets that arrive later, then it would be the router where the
ingress is attached that would generate the ICMP, never the (ingress)
interface whose MTU is insufficient.

Again, I'm in the process of updating draft-ietf-intarea-tunnels to be
much more clear on this point (the update should be issued in a day or two).

Joe