Re: [L2tpext] Propagating IP/ECN field when L2TP sits between IP as both L2 payload and PSN

Bob Briscoe <> Wed, 14 June 2017 11:20 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 5E36012708C for <>; Wed, 14 Jun 2017 04:20:36 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -2
X-Spam-Status: No, score=-2 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (2048-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id lU-kGHApS5Yi for <>; Wed, 14 Jun 2017 04:20:33 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id 9A8041201FA for <>; Wed, 14 Jun 2017 04:20:33 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed;; s=default; h=Content-Type:In-Reply-To:MIME-Version:Date: Message-ID:From:References:Cc:To:Subject:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=WbNm/9SWqLCzCt5kFcLF0BYOGA+3Lbv91hznuB/Ty60=; b=Ges125lx1KZOTBKbOB7iqkyyp 35xm2NF7arUBqI0bS9oomfuHy9yHVd5tqoKME55D167GpTNb22FG/EQxfPBuQnF7XdYO8Cb9FZ6Y3 OIrATe44Uf92w81P05nZ6cDks3oGPW97pIh8/THvRMIha8wjQkBaVPAJqwJ/cTnwQY295jmiSePQY AM/wWYwAo9hiPb1exDyLpH40iK5U0cbJcThgk0VF1rxawDMHlLQoH3rgOFwOfnPgzUl8qX8lwLYBo 7OpHRZBErz5E83ursygZZT5lhtVsT+Co+rV5o6IlNM29Yjur8HMiwZe7kbvi9/EUWKnsRczynUXlW VdWju0HZg==;
Received: from ([]:46730 helo=[]) by with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.89) (envelope-from <>) id 1dL6Lf-00051h-Ia; Wed, 14 Jun 2017 12:20:31 +0100
To: Ignacio Goyret <>
Cc: l2tp IETF list <>, "Black, David" <>
References: <> <> <> <>
From: Bob Briscoe <>
Message-ID: <>
Date: Wed, 14 Jun 2017 12:20:30 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1
MIME-Version: 1.0
In-Reply-To: <>
Content-Type: multipart/alternative; boundary="------------B75EF603C5DE621DCD489FC7"
Content-Language: en-GB
X-AntiAbuse: This header was added to track abuse, please include it with any abuse report
X-AntiAbuse: Primary Hostname -
X-AntiAbuse: Original Domain -
X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12]
X-AntiAbuse: Sender Address Domain -
X-Get-Message-Sender-Via: authenticated_id:
Archived-At: <>
Subject: Re: [L2tpext] Propagating IP/ECN field when L2TP sits between IP as both L2 payload and PSN
X-Mailman-Version: 2.1.22
Precedence: list
List-Id: Layer Two Tunneling Protocol Extensions <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Wed, 14 Jun 2017 11:20:36 -0000


On 31/05/17 02:51, Ignacio Goyret wrote:
> Note that things are a bit more complicated in v2 because
> it transports PPP packets, which may include IP packets (or portions
> of PPP packets if using Multilink). I have no issue punting on L2TPv2
> details.
While going back over all the emails in this thread (I am writing up the 
next rev of the draft), the above point raised a couple of questions in 
my mind:

Q1. When you say "portions" of IP packets, does L2TPv2 fragmented these 
as per IP fragmentation so that each 'portion' has an IP header, or are 
they carved up in a PPP-specific way without IP headers on each?

Q2. Does L2TPv3 support PPP in the same way?

Q3. Are there other L2 protocols currently supported by L2TPv3 that can 
carve up IP packets so that there will not be an IP header at the start 
of each payload?

If framing boundaries might be different, I will need to refer to 
section 5.6 of draft-ietf-tsvwg-ecn-encap-guidelines 
"Reframing and Congestion Markings", but I don't want to add complexity 
if it is not necessary.



Bob Briscoe