[mpls] Alexey Melnikov's Discuss on draft-ietf-mpls-rfc3107bis-02: (with DISCUSS and COMMENT)

Alexey Melnikov <aamelnikov@fastmail.fm> Tue, 01 August 2017 15:22 UTC

Return-Path: <aamelnikov@fastmail.fm>
X-Original-To: mpls@ietf.org
Delivered-To: mpls@ietfa.amsl.com
Received: from ietfa.amsl.com (localhost [IPv6:::1]) by ietfa.amsl.com (Postfix) with ESMTP id 71FB812EA95; Tue, 1 Aug 2017 08:22:03 -0700 (PDT)
MIME-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
From: Alexey Melnikov <aamelnikov@fastmail.fm>
To: "The IESG" <iesg@ietf.org>
Cc: draft-ietf-mpls-rfc3107bis@ietf.org, Loa Andersson <loa@pi.nu>, mpls-chairs@ietf.org, loa@pi.nu, mpls@ietf.org
X-Test-IDTracker: no
X-IETF-IDTracker: 6.58.0
Auto-Submitted: auto-generated
Precedence: bulk
Message-ID: <150160092345.9575.15101330200808959616.idtracker@ietfa.amsl.com>
Date: Tue, 01 Aug 2017 08:22:03 -0700
Archived-At: <https://mailarchive.ietf.org/arch/msg/mpls/aWIu8PFn_zXm2uI-6fYGOQJKAP8>
Subject: [mpls] Alexey Melnikov's Discuss on draft-ietf-mpls-rfc3107bis-02: (with DISCUSS and COMMENT)
X-BeenThere: mpls@ietf.org
X-Mailman-Version: 2.1.22
List-Id: Multi-Protocol Label Switching WG <mpls.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/mpls>, <mailto:mpls-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/mpls/>
List-Post: <mailto:mpls@ietf.org>
List-Help: <mailto:mpls-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/mpls>, <mailto:mpls-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 01 Aug 2017 15:22:03 -0000

Alexey Melnikov has entered the following ballot position for
draft-ietf-mpls-rfc3107bis-02: Discuss

When responding, please keep the subject line intact and reply to all
email addresses included in the To and CC lines. (Feel free to cut this
introductory paragraph, however.)


Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
for more information about IESG DISCUSS and COMMENT positions.


The document, along with other ballot positions, can be found here:
https://datatracker.ietf.org/doc/draft-ietf-mpls-rfc3107bis/



----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------

I would like to discuss one issue before recommending approval of this document:

In Section 2.1:

   The value field of the Multiple Labels Capability (shown in Figure 1)
   consists of one or more triples, where each triple consists of four
   octets.  The first two octets of a triple specify an AFI value, the
   third octet specifies a SAFI value, and the fourth specifies a Count.
   If one of the triples is <AFI,SAFI,Count>, the Count is the maximum
   number of labels that the BGP speaker sending the Capability can
   process in a received UPDATE of the specified AFI/SAFI.

I think lack of recommendations on the minimal supported Count value will
result in lack of interoperability. What are the common Count values used by
implementations?


----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

In Section 2.3:

      0                   1                   2                     3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+
     |    Length     |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 Label                 |Rsrv |S~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                 Label                 |Rsrv |S|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          Prefix                               ~
     ~                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 3: NLRI With Multiple Labels

   - Length:

      The Length field consists of a single octet.  It specifies the
      length in bits of the remainder of the NLRI field.

I would like to double check that my math is correct. With SAFI=128 and AFI=2,
assuming the prefix length of 192 bits, this will leave space for:

 (255-192)/24 = 2.625. So this configuration only allows for 2 labels to be included, right?