Re: [Pals] [Int-area] L2TP sequencing: Commonly disabled for IP data? Or always?

Stewart Bryant <stewart.bryant@gmail.com> Wed, 09 June 2021 11:50 UTC

Return-Path: <stewart.bryant@gmail.com>
X-Original-To: pals@ietfa.amsl.com
Delivered-To: pals@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 1E4AF3A111C; Wed, 9 Jun 2021 04:50:11 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.098
X-Spam-Level:
X-Spam-Status: No, score=-1.098 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, FREEMAIL_REPLY=1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=no autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
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 pJQEE2S82rFu; Wed, 9 Jun 2021 04:50:06 -0700 (PDT)
Received: from mail-wm1-x32d.google.com (mail-wm1-x32d.google.com [IPv6:2a00:1450:4864:20::32d]) (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 97C173A110B; Wed, 9 Jun 2021 04:50:06 -0700 (PDT)
Received: by mail-wm1-x32d.google.com with SMTP id 3-20020a05600c0243b029019f2f9b2b8aso4008222wmj.2; Wed, 09 Jun 2021 04:50:06 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=D5dw13OrhRSzE3FxPT/TcNLSrVzzA73VWO5Cjq6Ef24=; b=qCIO9qGJgMlDvtKfgRW8WOUmE0ygB4JpvUKhEZg0YI27mDcl/ylWqNsVRJOEwJOJCk mzSyGuaLeSy/oxuH3lXbXRHw3KJs+blo4b2LC2gsOVi0D7Og+qMQUk4MdAJu3pe4gEvf 4Kj4xooS2LgTJ+WF2qfKmdFO+zj87Ifjk9T8BvwcGSURXkao3Sh2fbqyBGG5xTM3fqSb gri9WXphNeE+i/CKGFf9IsWnIux20P7+a+KuWRaYuVZVwIjIP5hs+Q/NURADtKrKO7iV uAEgEmGrrvZHxRCyRsA1rFfxnx4/XQ6Y0qbPSTrjB4M97/6rVa6suOZ1K6O/fYoq8jYo NDsA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=D5dw13OrhRSzE3FxPT/TcNLSrVzzA73VWO5Cjq6Ef24=; b=E/GWD149Uy4IyjA/H3JCpvzSprQ5gD+pkR7BWlxjTCjTqQwYs51aOrlqPHSCq8Guuz LL+O8JdGjoCInnfrg2s7DIrwbgu1Mog8cbLP58I8TL+2zoSArViT1anVoAPWNNzStfbs lS75ItaDU2vqk9ibiihZ5bJkSGO1EiajtUee21ogVTp5/hacLMM8BY8tA1MOJ0YbWkRn JomLmfmrNdV/Iun1T5+4q6u7gQ6GPLQOMo33jQ6z7g6VNed+zmX3PirJcBVMHm3XNXbo DonZxB8g3WKFx2CcpMazeC5PNLCR5wwWzdif/RyGczedHb60b9awkdrPRr+PwxBMiBrs V5Jw==
X-Gm-Message-State: AOAM533knpASwmO7xy3xERHX+Aqp7jeeA1Jb+q/J7F50fpb5+LdqcWPY VSk/qhYRn9nOUX3fZeBK/mQ=
X-Google-Smtp-Source: ABdhPJw/j1eATZIJwsHfeVRMlyhvJOF8HcaGR0a/hxAGlg7f6HgsBa8lL56twU2dSumQ8f97SI6ecQ==
X-Received: by 2002:a1c:c3d7:: with SMTP id t206mr9351480wmf.23.1623239404518; Wed, 09 Jun 2021 04:50:04 -0700 (PDT)
Received: from [192.168.8.171] ([85.255.233.46]) by smtp.gmail.com with ESMTPSA id o5sm13521503wrw.65.2021.06.09.04.50.03 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Jun 2021 04:50:04 -0700 (PDT)
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.6\))
From: Stewart Bryant <stewart.bryant@gmail.com>
In-Reply-To: <aea7a88e-cca8-b3d5-ecf4-d162471e971d@joelhalpern.com>
Date: Wed, 9 Jun 2021 12:50:03 +0100
Cc: Stewart Bryant <stewart.bryant@gmail.com>, "Andrew G. Malis" <agmalis@gmail.com>, mark@townsley.net, "Carlos Pignataro (cpignata)" <cpignata@cisco.com>, Ignacio Goyret <ignacio.goyret@nokia.com>, intarea IETF list <int-area@ietf.org>, Derek Fawcus <dfawcus+lists-int-area@employees.org>, pals@ietf.org
Content-Transfer-Encoding: quoted-printable
Message-Id: <58F4227E-4F55-4618-9A56-E067BD31FA95@gmail.com>
References: <5c60cc79-1552-3f52-641f-e508780227ae@bobbriscoe.net> <YLuFLq7k9akVVHWS@clarinet.employees.org> <CAA=duU2o9YKF5Sfu6VTr5+bUr1JVgaGZh=X4+BQRbMu63FqVsg@mail.gmail.com> <5E252602-F635-4DF0-8FAE-C80CF88293D9@gmail.com> <aea7a88e-cca8-b3d5-ecf4-d162471e971d@joelhalpern.com>
To: Joel Halpern <jmh@joelhalpern.com>
X-Mailer: Apple Mail (2.3608.120.23.2.6)
Archived-At: <https://mailarchive.ietf.org/arch/msg/pals/pycbW-ikwwAZd7UxOF5uF2AxW2Y>
Subject: Re: [Pals] [Int-area] L2TP sequencing: Commonly disabled for IP data? Or always?
X-BeenThere: pals@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: "Pseudowire And LDP-enabled Services dicussion list." <pals.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/pals>, <mailto:pals-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/pals/>
List-Post: <mailto:pals@ietf.org>
List-Help: <mailto:pals-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/pals>, <mailto:pals-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 09 Jun 2021 11:50:11 -0000

Which applications still use it Joel?

Stewart

> On 9 Jun 2021, at 12:42, Joel M. Halpern <jmh@joelhalpern.com> wrote:
> 
> There is plenty of L2TP still in use.
> Yours,
> Joel
> 
> On 6/9/2021 6:23 AM, Stewart Bryant wrote:
>> Sequence number checking in the forwarder is always a problem because it is stateful so I doubt that many high-scale or high-speed forwarders ever did this.
>> I think there is an undisclosed assumption that go up enough levels and its IP so sequence number checking in the transport network (as opposed to the transport layer) is not really needed.
>> I doubt that there is much L2TP still out there. It was in its prime with dialup modems. L2TPv3 which was intended to replace it became niche with, as Andy says, operators who did not want MPLS. Much of what L2TPv3 was intended for was actually done with PW over MPLS with some replacement with by Mac in Mac for cost reasons.
>> If Carlos does not know the answer, Mark T would be my next port of call.
>> Stewart
>>> On 8 Jun 2021, at 22:41, Andrew G. Malis <agmalis@gmail.com <mailto:agmalis@gmail.com>> wrote:
>>> 
>>> Bob,
>>> 
>>> In addition to the cases listed by Derek, L2TPv3 can also carry non-IP pseudowire data, such as Ethernet frames (see RFC 4719 for example). Even though 4719 says that sequencing is optional, I would certainly recommend it :-).
>>> 
>>> But I guess that's really not what you were asking about, since you specifically mentioned IP data. But it is a case where you would probably see sequencing in use.
>>> 
>>> Back in the day, Sprint made good use of Ethernet over L2TPv3, as they were in the anti-MPLS camp at the time. But that's water over the bridge, and I really don't know if this solution continues to be in active use. Mark Townsley might know.
>>> 
>>> Cheers,
>>> Andy
>>> 
>>> 
>>> On Sat, Jun 5, 2021 at 10:07 AM Derek Fawcus <dfawcus+lists-int-area@employees.org <mailto:dfawcus%2Blists-int-area@employees.org>> wrote:
>>> 
>>>    On Fri, Jun 04, 2021 at 03:13:15PM +0100, Bob Briscoe wrote:
>>>    > The L2TP RFC says sequencing /can/ be disabled for IP data, but it
>>>    > doesn't say SHOULD or MUST. Is it possible that some operators
>>>    enable
>>>    > L2TP sequencing for IP data? And if so, do you know why they would?
>>>    > Also, are you aware of any other types of tunnel that might try
>>>    to keep
>>>    > IP data packets in sequence?
>>> 
>>>    How many intermediate headers are you considering between L2TP and
>>>    where
>>>    a carried IP header may exist?
>>> 
>>>    Maybe I'm getting the wrong end of the stick, but surely this engages
>>>    the text from section 5.4 of RFC 2661:
>>> 
>>>      "For example, if the PPP session being tunneled is not
>>>       utilizing any stateful compression or encryption protocols and is
>>>       only carrying IP (as determined by the PPP NCPs that are
>>>       established), then the LNS might decide to disable sequencing as IP
>>>       is tolerant to datagram loss and reordering."
>>> 
>>>    This would then suggest if L2TP is carrying PPP, the PPP session
>>>    is not
>>>    multi-link, and is making use of compression (including one of the
>>>    versions of IP header compression) in some form for IP packets, then
>>>    reordering will impact the ability to decompress.
>>> 
>>>    So such an L2TP data session may well make use of sequence numbers to
>>>    prevent reordering.
>>> 
>>>    I guess similarly in L2TPv3 when the PW is for PPP, and possibly also
>>>    the fragmentation scheme in RFC 4623 which requires sequence numbers;
>>>    and such PWE3 links could ultimately be carrying IP packets.
>>> 
>>> 
>>>    DF
>>> 
>>>    (not an operator)
>>> 
>>>    _______________________________________________
>>>    Int-area mailing list
>>>    Int-area@ietf.org <mailto:Int-area@ietf.org>
>>>    https://www.ietf.org/mailman/listinfo/int-area
>>>    <https://www.ietf.org/mailman/listinfo/int-area>
>>> 
>>> _______________________________________________
>>> Int-area mailing list
>>> Int-area@ietf.org <mailto:Int-area@ietf.org>
>>> https://www.ietf.org/mailman/listinfo/int-area
>> _______________________________________________
>> Int-area mailing list
>> Int-area@ietf.org
>> https://www.ietf.org/mailman/listinfo/int-area