Re: [mpls] The first nibble issue associated with MPLS encapsulation

Alexander Vainshtein <> Fri, 08 April 2016 19:31 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id B828C12D516; Fri, 8 Apr 2016 12:31:37 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.921
X-Spam-Status: No, score=-1.921 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (1024-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id PxsOUOFc9a9j; Fri, 8 Apr 2016 12:31:34 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by (Postfix) with ESMTPS id C01AB12D58E; Fri, 8 Apr 2016 12:31:32 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=selector1-ecitele-com; h=From:To:Date:Subject:Message-ID:Content-Type:MIME-Version; bh=YJZ464g5S6HzuLzW1RjymsrBHTZ9O+PX5WpBjUzTn2I=; b=cx0e1HTw7vycGxbYTEs0FTEbQlCKR7n6HKDNRxQYj1O4MPXilhl4CZrXBkAhPG4jvBeR8U8JqlYlwhBYoKrdg70GIigOuaFA1JN9dqUKCY0zp8zmACnHO9vHZXi0YbVztrrMZokIb5RjeGfGPMhRvSZHeZzz6zFQEZ19b1OnauU=
Received: from ( by ( with Microsoft SMTP Server (TLS) id 15.1.447.15; Fri, 8 Apr 2016 19:31:30 +0000
Received: from ([]) by ([]) with mapi id 15.01.0447.029; Fri, 8 Apr 2016 19:31:30 +0000
From: Alexander Vainshtein <>
To: "Carlos Pignataro (cpignata)" <>, Xiaohu Xu <>
Thread-Topic: [mpls] The first nibble issue associated with MPLS encapsulation
Thread-Index: AQHRkPR7Ow6l9wh8WUKpFJXl+MwAqJ+AqQ4A///PiXs=
Date: Fri, 08 Apr 2016 19:31:30 +0000
Message-ID: <>
References: <>, <>
In-Reply-To: <>
Accept-Language: en-US
Content-Language: en-US
authentication-results:; dkim=none (message not signed) header.d=none;; dmarc=none action=none;
x-originating-ip: []
x-ms-office365-filtering-correlation-id: 00ab3b3b-9438-4e93-8b95-08d35fe46304
x-microsoft-exchange-diagnostics: 1; DB3PR03MB0778; 5:rNtyABEHhCDUe2L/9LfAtLWr4zJTgk6bYn3jBsLaXKawHBRNOlWowL1TvqamfEKuZkPQU63neMo9osHDXuFO5Li5H6rtXVd3rRMYPG+emAw4tJKiDS1vGpZhPY7kqiqUGjmSRXgTGc1o8/y+lxXPEw==; 24:9O8J18ruzemFmYl3WI8DEU0r68Frh0aGgw4sH0r95qVNYdQYDQVE2ywQZX0qPVQ6z2OcOlJ3Fote+Co9NJJp5gp5QpISq3DijCdzuI+Qi6g=
x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:;SRVR:DB3PR03MB0778;
x-microsoft-antispam-prvs: <>
x-exchange-antispam-report-test: UriScan:(95692535739014);
x-exchange-antispam-report-cfa-test: BCL:0; PCL:0; RULEID:(601004)(2401047)(8121501046)(5005006)(3002001)(10201501046); SRVR:DB3PR03MB0778; BCL:0; PCL:0; RULEID:; SRVR:DB3PR03MB0778;
x-forefront-prvs: 0906E83A25
x-forefront-antispam-report: SFV:NSPM; SFS:(10019020)(24454002)(13464003)(52034003)(377454003)(10400500002)(11100500001)(95246002)(5008740100001)(19580405001)(19580395003)(86362001)(586003)(3846002)(164054004)(1096002)(5004730100002)(3660700001)(3280700002)(1220700001)(9686002)(102836003)(6116002)(92566002)(4326007)(33646002)(19617315012)(2906002)(50986999)(76176999)(54356999)(66066001)(16236675004)(5002640100001)(5001770100001)(15975445007)(106116001)(77096005)(189998001)(2900100001)(81166005)(87936001)(122556002)(2950100001)(51650200001); DIR:OUT; SFP:1102; SCL:1; SRVR:DB3PR03MB0778;; FPR:; SPF:None; MLV:sfv; LANG:en;
spamdiagnosticoutput: 1:23
spamdiagnosticmetadata: NSPM
Content-Type: multipart/alternative; boundary="_000_mc51yrrf9n0wxbjsrprt9amf1460143890063emailandroidcom_"
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-originalarrivaltime: 08 Apr 2016 19:31:30.5765 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 2c514a61-08de-4519-b4c0-921fef62c42a
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB3PR03MB0778
Archived-At: <>
Cc: "" <>, "" <>, "" <>, "Dr. Tony Przygienda" <>
Subject: Re: [mpls] The first nibble issue associated with MPLS encapsulation
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Multi-Protocol Label Switching WG <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Fri, 08 Apr 2016 19:31:38 -0000

Carlos and all,
Just for the reference, IANA has defined version 5 (0101) has assigned to ST protocol and refers to RFC 1119. The latter has been obsoleted by RFC 1819, but the IANA
assignment still holds.

Is there, just in case, any relationship between BIER and ST?
Thumb typed on my cellphone

-------- Original Message --------
From: "Carlos Pignataro (cpignata)" <>
Date: Fri, April 08, 2016 9:25 PM +0300
To: Xiaohu Xu <>
CC:,,, "Dr. Tony Przygienda" <>
Subject: Re: [mpls] The first nibble issue associated with MPLS encapsulation

Xiaohu, Tony,

Please see inline.

On Apr 7, 2016, at 2:39 PM, Xuxiaohu <<>> wrote:

As for the first nibble issue, will it violate the layering principle of network protocol stacks if the first nibble of any new encapsulation header (which could be an MPLS payload) is used as the "MPLS payload type" field?

Reading draft-wang-bier-ethernet-01, Section 3, the "first nibble" is _not_ used as an "MPLS payload type". Instead, the text describes an anti-aliasing mechanism, much like RFC 4928.

The relevant text is:
     First nibble: The first 4 bits of the header are set to 0101; this
   ensures that the BIER header will not be confused with an IP header
   or with the header of a pseudowire packet.

Which says "... will not be confused with ..."

wouldn't it  be more reasonable and sustainable to fix the problem (i.e., the lack of a protocol field in the MPLS header) by the MPLS header itself?

Who says it is a *problem*? There's no "fixing" needed.

By the way, since it's claimed that the NSH is transport-independant, it means the NSH should be able to be transported over MPLS. However, it seems that the first nibble issue has not be considered in the current NSH draft. As a result, when encapsulating NSH over MPLS, the NSH may be mis-interpreted as IP header.

There seems to be some massive confusion on this paragraph, on a number of levels. First, NSH is not "claimed to be" transport-independent. It is by charter and by design. Second, the NSH draft does not even include the term "MPLS", because it does not define transports. The SFC Encapsulation can be used in a transport-agnostic way.

One more comment below.

Best regards,

???: BIER [<>] ?? Tony Przygienda [<>]
????: 2016?4?5? 22:36
??: [Bier] comments on draft-wang-bier-ethernet-01

after reading

a) first nibble: refer to MPLS encaps as "the same value" to keep in sync

One comment regarding the "First nibble" text at draft-ietf-bier-mpls-encapsulation-03

Since the function of the first nibble is to prevent aliasing with an IP packet, in order for RFC 4928 to specify values of 0x0 and 0x1 for the First Nibble, it had to "Reserve" IP protocol versions of 0 and 1, referencing that RFC (see

Is the intent to re-assign IPv5 at ?

Note that RFC 4928 says "REQUIRED" at:

   It is REQUIRED, however, that applications depend upon in-order
   packet delivery restrict the first nibble values to 0x0 and 0x1.


- Carlos.

b) refer to all other possible fields to MPLS encaps to keep in sync when describing instead of repeating
c) you need to describe which kind of ether MACs are allowed, especially on broadcast media, i.e. is it always p2p or can you take advantage of the broadcast ?
d) Figure 4: use the architecture/MPLS encoding for the length, don't invent a new one
e) who will obtain a new ether type from IEEE? As far I understand, not a trivial process albeit we have several liaisons with IEEE

We've heard that a million monkeys at a million keyboards could produce the complete works of Shakespeare; now, thanks to the Internet, we know that is not true.
?Robert Wilensky
mpls mailing list<>