Re: [bess] Encoding a 20 bit label in a 24 bit field.

"Jakob Heitz (jheitz)" <> Tue, 16 October 2018 01:23 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id 8BB581277BB for <>; Mon, 15 Oct 2018 18:23:47 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -14.565
X-Spam-Status: No, score=-14.565 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.064, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, RCVD_IN_DNSWL_HI=-5, SPF_PASS=-0.001, USER_IN_DEF_DKIM_WL=-7.5] 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 jhmK3_U6-L6m for <>; Mon, 15 Oct 2018 18:23:44 -0700 (PDT)
Received: from ( []) (using TLSv1.2 with cipher DHE-RSA-SEED-SHA (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id ADD0A127333 for <>; Mon, 15 Oct 2018 18:23:44 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple;;; l=4110; q=dns/txt; s=iport; t=1539653024; x=1540862624; h=from:to:subject:date:message-id:references:in-reply-to: content-transfer-encoding:mime-version; bh=6q2OI8QzFP8cb1UgrHl0mmllDLxLtW9+agAZKvxby0k=; b=S6f9/WalVPaAlN0GhwypRFAKEsB9dTJLCya1cdReBWvRyZmmmZkxEvWA +eaZVwRN74BYSQ3yIRdFGZkyzrjhR52UF3WNa7TIzt9FAGROHgpTKC1Rq KdUvJmbGcOBvLiKqiieq31LXnrgDyLIYSdWC9LGAaVPmmHXMWaL5HqFhf U=;
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-AV: E=Sophos;i="5.54,386,1534809600"; d="scan'208";a="466866656"
Received: from ([]) by with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 16 Oct 2018 01:23:43 +0000
Received: from ( []) by (8.15.2/8.15.2) with ESMTPS id w9G1Nhju007925 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=FAIL); Tue, 16 Oct 2018 01:23:43 GMT
Received: from ( by ( with Microsoft SMTP Server (TLS) id 15.0.1395.4; Mon, 15 Oct 2018 20:23:43 -0500
Received: from ([]) by ([]) with mapi id 15.00.1395.000; Mon, 15 Oct 2018 20:23:42 -0500
From: "Jakob Heitz (jheitz)" <>
To: Zhuangshunwan <>, BESS <>
Thread-Topic: Encoding a 20 bit label in a 24 bit field.
Thread-Index: AdRkxCtHf3jUpftBTCqhT2pNBUyBrwAJXZGwAAEes/A=
Date: Tue, 16 Oct 2018 01:23:42 +0000
Message-ID: <>
References: <> <>
In-Reply-To: <>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: []
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Archived-At: <>
Subject: Re: [bess] Encoding a 20 bit label in a 24 bit field.
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: BGP-Enabled ServiceS working group discussion list <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 16 Oct 2018 01:23:48 -0000

How about:
The lower order 4 bits SHOULD be sent as 0 and ignored on receipt.


-----Original Message-----
From: Zhuangshunwan <> 
Sent: Monday, October 15, 2018 6:02 PM
To: Jakob Heitz (jheitz) <>; BESS <>
Subject: RE: Encoding a 20 bit label in a 24 bit field.

It is good to make this explicit. This ambiguity has led to some unnecessary interworking problems.

Should we also need to explicitly define the "bottom of stack" bit in the low-order bit of the 3-octet label field?


-----Original Message-----
From: BESS [] On Behalf Of Jakob Heitz (jheitz)
Sent: Tuesday, October 16, 2018 4:21 AM
To: BESS <>
Subject: [bess] Encoding a 20 bit label in a 24 bit field.

We have proposed the following erratum for RFC 7432.



-----Original Message-----
From: RFC Errata System <>
Sent: Friday, October 12, 2018 12:37 PM
To: Ali Sajassi (sajassi) <>;;;;;;;;;; Giles Heron (giheron) <>;
Cc: Krishnamoorthy Arumugham (karumugh) <>;;
Subject: [Technical Errata Reported] RFC7432 (5523)

The following errata report has been submitted for RFC7432, "BGP MPLS-Based Ethernet VPN".

You may review the report below and at:

Type: Technical
Reported by: Krishnamoorthy Arumugham <>

Section: 7

Original Text
Clarifications to following sub-sections:
Section 7.1
Section 7.2
Section 7.5

Corrected Text
Section 7.1:
Add below text to the section 7.1 regarding the encoding of MPLS label:

"The value of the 20-bit MPLS label is encoded in the high-order 20 bits of the 3 bytes MPLS Label field."

Section 7.2:
Add below text to the section 7.2 regarding the encoding of both the MPLS label fields:

"The value of the 20-bit MPLS label is encoded in the high-order 20 bits of the 3 bytes MPLS Label field for both MPLS Label1 and MPLS Label2."

Section 7.5:
Add below text to the section 7.5 regarding the encoding of ESI Label fields:

"The value of the 20-bit MPLS label is encoded in the high-order 20 bits of the ESI Label field."

MPLS label is a 20-bit value and is stored in a 3 bytes field in a packet. The 20-bit MPLS label value is generally stored in higher order 20 bits of the 3 byte label field. The exact encoding to be followed for storing MPLS label values are not explicitly mentioned in the RFC 7432 under section 7.1, 7.2 and 7.5 for different types of EVPN routes. This lead to ambiguity in different implementations. Hence a clarification is required.

This erratum is currently posted as "Reported". If necessary, please
use "Reply All" to discuss whether it should be verified or
rejected. When a decision is reached, the verifying party  
can log in to change the status and edit the report, if necessary. 

RFC7432 (draft-ietf-l2vpn-evpn-11)
Title               : BGP MPLS-Based Ethernet VPN
Publication Date    : February 2015
Author(s)           : A. Sajassi, Ed., R. Aggarwal, N. Bitar, A. Isaac, J. Uttaro, J. Drake, W. Henderickx
Category            : PROPOSED STANDARD
Source              : Layer 2 Virtual Private Networks
Area                : Routing
Stream              : IETF
Verifying Party     : IESG

BESS mailing list