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

Fernando Gont <fgont@si6networks.com> Thu, 02 February 2017 11:08 UTC

Return-Path: <fgont@si6networks.com>
X-Original-To: ietf@ietfa.amsl.com
Delivered-To: ietf@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 92CBC129437; Thu, 2 Feb 2017 03:08:20 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.901
X-Spam-Level:
X-Spam-Status: No, score=-1.901 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-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 561yEwHHc7Wt; Thu, 2 Feb 2017 03:08:14 -0800 (PST)
Received: from fgont.go6lab.si (fgont.go6lab.si [91.239.96.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 9E4E7127076; Thu, 2 Feb 2017 03:08:14 -0800 (PST)
Received: from [IPv6:2001:1291:200:42e::2] (cl-1071.udi-01.br.sixxs.net [IPv6:2001:1291:200:42e::2]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by fgont.go6lab.si (Postfix) with ESMTPSA id 36D8380A93; Thu, 2 Feb 2017 12:08:09 +0100 (CET)
Subject: Re: Last Call: <draft-ietf-6man-rfc1981bis-04.txt> (Path MTU Discovery for IP version 6) to Internet Standard
To: "Eggert, Lars" <lars@netapp.com>
References: <148599312602.18643.4886733052828400859.idtracker@ietfa.amsl.com> <1859B1D9-9E42-4D65-98A8-7A326EDDE560@netapp.com> <f8291774-409e-2948-3b29-83dbb09d39d9@si6networks.com> <5C876EB6-F2B6-4F2C-9A6B-2AC63D0115D3@netapp.com>
From: Fernando Gont <fgont@si6networks.com>
X-Enigmail-Draft-Status: N1110
Message-ID: <4de97844-6f79-058c-e284-2b9ae79147fe@si6networks.com>
Date: Thu, 02 Feb 2017 07:58:17 -0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1
MIME-Version: 1.0
In-Reply-To: <5C876EB6-F2B6-4F2C-9A6B-2AC63D0115D3@netapp.com>
Content-Type: text/plain; charset="windows-1252"
Content-Transfer-Encoding: 7bit
Archived-At: <https://mailarchive.ietf.org/arch/msg/ietf/Kqy-YoQ8tI4HI5AkKDQqT6dh-fI>
Cc: "ipv6@ietf.org" <ipv6@ietf.org>, "6man-chairs@ietf.org" <6man-chairs@ietf.org>, "tsv-area@ietf.org" <tsv-area@ietf.org>, "ietf@ietf.org" <ietf@ietf.org>, "draft-ietf-6man-rfc1981bis@ietf.org" <draft-ietf-6man-rfc1981bis@ietf.org>
X-BeenThere: ietf@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: IETF-Discussion <ietf.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ietf>, <mailto:ietf-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ietf/>
List-Post: <mailto:ietf@ietf.org>
List-Help: <mailto:ietf-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ietf>, <mailto:ietf-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 02 Feb 2017 11:08:20 -0000

On 02/02/2017 07:21 AM, Eggert, Lars wrote:
> On 2017-2-2, at 10:54, Fernando Gont <fgont@si6networks.com> wrote:
>> On 02/02/2017 06:37 AM, Eggert, Lars wrote:
>>> Also, even if ICMP delivery is assured, there are additional 
>>> complications for UDP, which has been seeing a lot of interest
>>> both as a tunneling encapsulation and for applications (e.g.,
>>> QUIC). Many platforms do not provide UDP-sending applications any
>>> information about arriving ICMP messages that were triggered by
>>> their transmissions. So even if the path delivers ICMP, the OS
>>> makes ICMP-based PMTUD for UDP often impossible. Another reason
>>> to recommend 4821?
>> 
>> Agreed... although in this case this would be more of an app-layer 
>> implementation than one at the transport layer?
> 
> There are two dimensions here, one is in kernel vs. in userspace, the
> other which "layer" something is at. It used to be that "transport
> layer" (or "network layer" always implied "in kernel", but those days
> are past.

I was refering to "layer" as in a reference model. i.e., PMTU assumes
that you can repacketize your data. For TCP, that can be done at the
transport layer, since it's byte-stream oriented. OTOH, UDP is
essentially record-based... so any "re-packetization" must be done at
the upper (app) layer.

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492