Network Working Group                                       Simon Delord
Internet Draft                                               Raymond Key
Category: Standard Track                                         Telstra
Expires: April 2010
                                                         Frederic Jounay
                                                          France Telecom

                                                          Wim Henderickx
                                                          Alcatel-Lucent

                                                               Lucy Yong
                                                                  Huawei


                                                        October 07, 2009



            Control Word Reserved bit for use in E-Tree
              draft-delord-pwe3-cw-bit-etree-00.txt



Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 07, 2010.







Delord et al.               Expires April 2010               [Page 1]


Internet Draft           CW bit for use in E-Tree          October 2009


Abstract

   The extension described in this document allows a pair of PEs
   connected via an Ethernet Pseudowire (PW) to signal via the use of
   the Control Word (CW) whether the Ethernet frame encapsulated is
   coming from a Root AC or a Leaf AC. This allows a PE receiving this
   frame to decide whether it can be forwarded to a Leaf AC or not.
   Such forward or drop decision is an additional filtering action
   after the MAC-based forwarding decision. This applies to both P2P PW
   and P2MP PW.

Conventions used in this document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].


Table of Contents


   1. Introduction....................................................3
   2. Terminology.....................................................3
   3. Scope and Applicability.........................................4
   3.1. Scope Problem.................................................4
   3.2. Applicability.................................................5
   4. Control Word Extensions.........................................5
   4.1. Ethernet Control Word Reserved Bit............................5
   5. Procedures......................................................6
   5.1. Detailed PE PW Setup Procedures...............................6
   5.2. Detailed PE Forwarding Procedures.............................6
   5.2.1. Forwarding PE...............................................6
   5.2.2. Receiving PE................................................7
   6. Security Considerations.........................................7
   7. IANA Considerations.............................................7
   8. Acknowledgments.................................................7
   9. References......................................................7
   9.1. Normative References..........................................7
   9.2. Informative References........................................7
   Authors' Addresses.................................................8
   Intellectual Property and Copyright Statements.....................8











Delord et al.               Expires April 2010               [Page 2]


Internet Draft           CW bit for use in E-Tree          October 2009


1. Introduction

   This document proposes to use a specific bit within the Control Word
   (CW) present on top of an Ethernet PW for a PE to indicate to a
   remote PE connected via a Pseudowire (PW) whether the Ethernet frame
   carried comes from a Root AC or a Leaf AC in an E-Tree construct
   using VPLS. This applies to both P2P PW and P2MP PW.

   [RFC4385] describes the preferred design of a Pseudowire Emulation
   Edge-to-Edge (PWE3) Control Word to be used over an MPLS packet
   switched network.

   [RFC4447] specifies extensions to Label Distribution Protocol (LDP)
   for PEs to setup PWs. It also describes the procedures for PEs to
   signal to each other whether the CW is to be used or not.

   [RFC4448] describes specifies the encapsulation of Ethernet/802.3
   PDUs within a PW.

2. Terminology

   E-Tree

   An Ethernet VPN in which each Root AC can communicate with every
   other type of AC, whereas Leaf ACs can only communicate with Root
   ACs. Each AC on an E-Tree construct is designated as either a Root
   AC or a Leaf AC. There can be multiple Root ACs and Leaf ACs per
   E-Tree construct.

   Root AC

   An ingress frame at a Root AC can be delivered to one or more of
   any of the other ACs in the E-Tree. Please note that this AC is
   bidirectional.

   Leaf AC

   Ingress frame at a Leaf AC can only be delivered to one or more Root
   ACs in the E-Tree. Ingress frame at a Leaf AC MUST NOT be delivered
   to any Leaf ACs in the E-Tree. Please note that this AC is
   bidirectional.











Delord et al.               Expires April 2010               [Page 3]


Internet Draft           CW bit for use in E-Tree          October 2009


   3. Scope and Applicability

   3.1. Scope & Problem

   One important application for carriers is the deployment of E-Tree
   services over an MPLS backbone using VPLS.

                    +---------+          +---------+
                    |   PE1   |          |   PE2   |
                    |         |          |         |
   +---+            |  +---+  |          |  +---+  |            +---+
   |CE1+-----AC1----+--+   |  |          |  |   +--+----AC3-----+CE3|
   +---+  (Root AC) |  | V |  |          |  | V |  | (Root AC)  +---+
                    |  |   |  | Ethernet |  |   |  |
                    |  | S +--+----PW----+--+ S |  |
   +---+            |  |   |  |          |  |   |  |            +---+
   |CE2+-----AC2----+--+ I |  |          |  | I +--+----AC4-----+CE4|
   +---+  (Leaf AC) |  |   |  |          |  |   |  | (Leaf AC)  +---+
                    |  +---+  |          |  +---+  |
                    |         |          |         |
                    +---------+          +---------+
                     <---------- E-Tree ---------->

                  Figure 1. E-Tree over MPLS using VPLS

   Figure 1 describes a typical use case where PE1 and PE2 need to
   establish an E-Tree construct between different Ethernet endpoints.
   Each PE has 2 ACs connected to a VSI. These VSIs are then linked
   together via an Ethernet PW.

   AC1 is a Root AC on PE1 and AC2 is a Leaf AC on PE1.

   AC3 is a Root AC on PE2 and AC4 is a Leaf AC on PE2.

   With an E-Tree construct:
      - AC1 can receive from and transmit to AC2, AC3 and AC4
      - AC3 can receive from and transmit to AC1, AC2 and AC4
      - AC2 and AC4 can receive from and transmit to AC1 and AC3
      - AC2 and AC4 cannot receive from or transmit to each other

   When an Ethernet Frame is received on PE1 via AC1, the frame can be
   transmitted to AC2 and via the Ethernet PW connecting PE1 and PE2 to
   AC3 and AC4.

   However when an Ethernet Frame is received on PE1 via AC2, the frame
   can be transmitted to AC3 via the Ethernet PW but not to AC4.






Delord et al.               Expires April 2010               [Page 4]


Internet Draft           CW bit for use in E-Tree          October 2009


   When PE2 receives an Ethernet frame from PE1 via the Ethernet PW,
   there is no indication whether it is from AC1 or AC2, PE2 is
   therefore unable to decide whether it can be forwarded to AC4 as per
   the E-Tree construct.

   3.2. Applicability

   The proposed approach in this document will allow PE2 to make a
   decision for each Ethernet frame arriving on the PW from PE1 whether
   this frame can be forwarded towards a Leaf AC.

   Obviously, each PE is also responsible for locally identifying which
   ACs are Root ACs or Leaf ACs and for not forwarding Ethernet frames
   between Leaf ACs. Most common procedure for doing so is to apply a
   split horizon rule between Leaf ACs. However this is out of scope of
   this document.

   4. Control Word Extensions

   4.1. Ethernet Control Word Reserved Bit

   [RFC4448] defines in section 4.6 the CW format for an Ethernet PW.

   The Control Word defined in this section is based on the Generic PW
   MPLS Control Word as defined in [RFC4385].  It provides the ability
   to sequence individual frames on the PW, avoidance of equal-cost
   multiple-path load-balancing (ECMP), and Operations and
   Management (OAM) mechanisms including VCCV.

   The Control Word is defined as follows:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0 0 0 0|L| Reserved            |       Sequence Number         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   In the above diagram, the first 4 bits MUST be set to 0 to indicate
   PW data.

   Leaf bit (L).

   The L-bit is used to flag the presence of an Ethernet frame from
   a Leaf AC as follows:

       L = 1 The Ethernet Frame comes from a Leaf AC
       L = 0 The Ethernet Frame comes from a Root AC

   The rest of the first 16 bits are reserved for future use. They MUST
   be set to 0 when transmitting, and MUST be ignored upon receipt.


Delord et al.               Expires April 2010               [Page 5]


Internet Draft           CW bit for use in E-Tree          October 2009


   The next 16 bits provide a sequence number that can be used to
   guarantee ordered frame delivery.  The processing of the sequence
   number field is OPTIONAL.

   The sequence number space is a 16-bit, unsigned circular space.  The
   sequence number value 0 is used to indicate that the sequence number
   check algorithm is not used.  The sequence number processing
   algorithm is found in [RFC4385].

   5. Procedures

   [RFC4447] defines the procedures by which PEs maintain and exchange
   PW information via LDP.

   This document does not change any of the procedures defined in
   [RFC4447]. The rules for negociating the use of the CW are defined
   in section 6.

   5.1. Detailed PE PW Setup Procedures

   In order for a PEs to signal if an Ethernet frame travelling on an
   Ethernet PW comes from a Root AC or a Leaf AC, it MUST use the
   extension defined in this document.

   The procedure MUST follow the standard procedures described in
   [RFC4447].

   The Label Mapping messages that are sent in order to set up these
   PWs MUST have c=1.  When a Label Mapping message for a PW of one
   of these types is received and c=0, a Label Release message MUST
   be sent, with an "Illegal C-bit" status code.  In this case, the
   PW will not be enabled.

   5.2. Detailed PE Forwarding Procedures

   5.2.1. Forwarding PE

   The L-bit MUST only be used when the first 4 bits of the CW are
   equal to 0000.

   The L-bit MUST be set to 0 when the first 4 bits of the CW are equal
   to 0001.

   If the Ethernet frame that has to be sent across an Ethernet PW (or
   set of Ethernet PWs) comes from a Root AC, the L bit MUST be set to
   0.

   If the Ethernet frame that has to be sent across an Ethernet PW (or
   set of Ethernet PWs) comes from a Leaf AC, the L bit MUST be set to
   1.


Delord et al.               Expires April 2010               [Page 6]


Internet Draft           CW bit for use in E-Tree          October 2009


5.2.2 Receiving PE

   Upon reception of an Ethernet Frame where the L bit in the CW is set
   to 0, this frame can be forwarded to any AC belonging to this VPN
   instance.

   Upon reception of an Ethernet Frame where the L bit in the CW is set
   to 1, this frame can be forwarded to any Root AC belonging to this
   VPN instance but it MUST NOT be forwarded to any Leaf AC. This
   forward or drop decision is an additional filtering action after the
   MAC-based forwarding decision.

6. Security Considerations

   This section will be added in a future version.

7. IANA Considerations

   There are no specific IANA considerations in this document.

8. Acknowledgments

   The authors would like to acknowledge Lizhong Jin for his support
   and feedback.

9. References

9.1. Normative References

   [RFC2119]    Bradner, S., Key words for use in RFCs to Indicate
                Requirement Levels, BCP 14, RFC 2119, March 1997.

   [RFC4385]    Bryant,S., Swallow, G., and Al, Pseudowire Emulation
                Edge-to-Edge (PWE3) Control Word for Use over an MPLS
                PSN, February 2006.

   [RFC4447]    Martini, L., and al, Pseudowire Setup and Maintenance
                Using the Label Distribution Protocol (LDP), April 2006

   [RFC4448]    Martini, L., and al, Encapsulation Methods for
                Transport of Ethernet over MPLS Networks, April 2006

9.2. Informative References









Delord et al.               Expires April 2010               [Page 7]


Internet Draft           CW bit for use in E-Tree          October 2009


Author's Addresses

   Simon Delord
   Telstra
   242 Exhibition St
   Melbourne VIC 3000
   Australia
   Email: simon.a.delord@team.telstra.com

   Frederic Jounay
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   France
   Email: frederic.jounay@orange-ftgroup.com

   Raymond Key
   Telstra
   242 Exhibition St
   Melbourne VIC 3000
   Australia
   Email: raymond.key@team.telstra.com

   Wim Henderickx
   Alcatel-Lucent
   Copernicuslaan 50
   2018 Antwerp, Belgium
   Email: wim.henderickx@alcatel-lucent.be

   Lucy Yong
   Huawei USA
   1700 Alma Dr. Suite 500
   Plano, TX  75075
   Email: lucyyong@huawei.com


   Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your
   rights and restrictions with respect to this document.






Delord et al.               Expires April 2010               [Page 8]