Network Working Group Simon Delord, Alcatel-Lucent Internet Draft Raymond Key, Huawei Category: Standard Track Frederic Jounay, Orange France Telecom Expires: April 2012 Wim Henderickx, Alcatel-Lucent Lucy Yong, Huawei Lizhong Jin, ZTE October 16, 2011 Control Word Reserved bit for use in E-Tree draft-delord-pwe3-cw-bit-etree-06 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 16, 2012. 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. Delord et al. Expires April 2012 [Page 1] Internet Draft CW bit for use in E-Tree October 2011 Table of Contents 1. Introduction....................................................3 2. Terminology.....................................................3 3. Scope and Applicability.........................................4 3.1. Scope & Problem...............................................4 3.2. Proposed Approach.............................................5 3.3. Applicability.................................................5 4. Control Word Extensions.........................................6 4.1. Ethernet Control Word Reserved Bit............................6 5. Procedures......................................................7 5.1. Detailed PE PW Setup Procedures...............................7 5.2. Detailed PE Forwarding Procedures.............................7 5.2.1. Forwarding PE...............................................7 5.2.2. Receiving PE................................................7 6. Security Considerations.........................................8 7. IANA Considerations.............................................8 8. Acknowledgments.................................................8 9. References......................................................8 9.1. Normative References..........................................8 9.2. Informative References........................................8 Authors' Addresses.................................................9 Intellectual Property and Copyright Statements.....................9 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]. Delord et al. Expires April 2012 [Page 2] Internet Draft CW bit for use in E-Tree October 2011 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] specifies the encapsulation of Ethernet/802.3 PDUs within a PW. [Draft VPLS ETree Req] provides the functional requirements for MEF E-Tree support in VPLS. 2. Terminology E-Tree An Ethernet VPN in which each Root AC can communicate with every other 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 2012 [Page 3] Internet Draft CW bit for use in E-Tree October 2011 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 scenario 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 2012 [Page 4] Internet Draft CW bit for use in E-Tree October 2011 When PE2 receives an Ethernet frame from PE1 via the Ethernet PW, there is no indication whether it is from a Leaf AC or a Root AC, PE2 is therefore unable to decide whether it can be forwarded to AC4 (Leaf AC) as per the E-Tree construct. 3.2. Proposed Approach A simple fix to this problem is to carry one additional bit of information (0 or 1) for each Ethernet payload frame on the Ethernet PW. This per-payload signaling approach indicates whether the payload frame is from a Leaf AC or a Root AC on the ingress PE. Based on this per-payload extra-information, the egress PE can decide whether the payload frame can be forwarded to a Leaf AC or not. [RFC4385] defines in section 3 the Preferred PW MPLS Control Word. 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| Flags |FRG| Length | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Flags (bits 4 to 7): These bits MAY be used by for per-payload signaling. Their semantics MUST be defined in the PW specification. [RFC4448] defines in section 4.6 the Control Word for Ethernet PW. 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| Reserved | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Flags (bits 4 to 7 of the Control Word) are "reserved for future use" bits in the current Ethernet PW standard that can be used for such per-payload signaling. 3.3. Applicability The proposed approach in this document will allow the egress PE to make a decision for each Ethernet frame arriving on the PW from the ingress PE whether this frame can be forwarded towards a Leaf AC. Delord et al. Expires April 2012 [Page 5] Internet Draft CW bit for use in E-Tree October 2011 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. The 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. 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]. Delord et al. Expires April 2012 [Page 6] Internet Draft CW bit for use in E-Tree October 2011 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 negotiating 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. 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. Delord et al. Expires April 2012 [Page 7] Internet Draft CW bit for use in E-Tree October 2011 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 will be added in later version of this document. 7. IANA Considerations There are no specific IANA considerations in this document. 8. Acknowledgments The authors would like to thank Yuji Kamite for his valuable comments. 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 [Draft VPLS ETree Req] Key, et al., Requirements for MEF E-Tree Support in VPLS, draft-ietf-l2vpn-etree-reqt-00 (work in progress), October 2011 Delord et al. Expires April 2012 [Page 8] Internet Draft CW bit for use in E-Tree October 2011 Authors' Addresses Simon Delord Alcatel-Lucent Email: simon.delord@gmail.com Raymond Key Huawei Email: raymond.key@ieee.org Frederic Jounay Orange France Telecom 2, avenue Pierre-Marzin 22307 Lannion Cedex, France Email: frederic.jounay@orange.com Wim Henderickx Alcatel-Lucent Copernicuslaan 50 2018 Antwerp, Belgium Email: wim.henderickx@alcatel-lucent.com Lucy Yong Huawei USA 1700 Alma Dr. Suite 500 Plano, TX 75075, USA Email: lucy.yong@huawei.com Lizhong Jin ZTE Corporation 889, Bibo Road Shanghai, 201203, China Email: lizhong.jin@zte.com.cn Copyright Notice Copyright (c) 2011 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 (http://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Delord et al. Expires April 2012 [Page 9]