Network Working Group Rahul Aggarwal Internet Draft XiPeng Xiao Expiration Date: May 2003 Redback Networks W. Mark Townsley Stewart Bryant Cisco Systems Cheng-Yin Lee Alcatel Tissa Senevirathne Consultant Mitsuru Higashiyama Anritsu Corporation Transport of Ethernet Frames over L2TPv3 draft-ietf-l2tpext-pwe3-ethernet-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026, except that the right to produce derivative works is not granted. 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. Abstract This document describes transport of Ethernet frames over Layer 2 Tunneling Protocol (L2TPv3). This includes the transport of Ethernet port to port frames as well as the transport of Ethernet VLAN frames. The mechanism described in this document can be used in the creation of Pseudo Wires to transport Ethernet frames over an IP network. draft-ietf-l2tpext-pwe3-ethernet-00.txt [Page 1] Internet Draft draft-ietf-l2tpext-pwe3-ethernet-00.txt October 2002 Table of Contents 1 Introduction........................................ 2 1.1 Abbreviations....................................... 2 1.2 Requirements........................................ 2 2 PW Establishment.................................... 3 2.1 LCCE-LCCE Control Connection Establishment.......... 3 2.2 PW Session Establishment............................ 4 2.3 PW Session Monitoring............................... 4 2.3.1 SLI Message......................................... 4 3 Packet Processing................................... 5 3.1 Encapsulation....................................... 5 3.2 Sequencing.......................................... 5 3.3 MTU Handling........................................ 6 4 Security Considerations............................. 6 5 IANA Considerations................................. 6 6 Acknowledgements.................................... 6 7 References.......................................... 6 8 Author Information.................................. 7 1. Introduction L2TPv3 can be used as a control protocol and for data encapsulation to set up Pseudo Wires (PW) for transporting layer 2 Packet Data Units across an IP network [L2TPv3]. This document describes the transport of Ethernet frames over L2TPv including the PW establishment and data encapsulation. 1.1 Abbreviations CE Customer Edge. (Typically also the L2TPv3 Remote System) LCCE L2TP Control Connection Endpoint (See [L2TPv3]) PE Provider Edge (Typically also the LCCE). PSN Packet Switched Network PW Pseudo-Wire PWE3 Pseudo-Wire Emulation Edge to Edge (Working Group) NSP Native Service Processing 1.2. Requirements An Ethernet PW emulates a single Ethernet link between exactly two endpoints. The following figure depicts the PW termination relative to the NSP and PSN tunnel within a LCCE [PWE3-LAYER]. The CE in this figure is typically also the L2TPv3 Remote System. The LCCE may or may not be a PE. draft-ietf-l2tpext-pwe3-ethernet-00.txt [Page 2] Internet Draft draft-ietf-l2tpext-pwe3-ethernet-00.txt October 2002 +---------------------------------------+ | LCCE | +----+ +-+ +-----+ +------+ +------+ +-+ | | |P| | | |PW ter| | PSN | |P| | C |<==>|h|<=>| NSP |<=>|minati|<=>|Tunnel|<=>|h|<==> PSN | E | |y| | | |on | | | |y| | | +-+ +-----+ +------+ +------+ +-+ +----+ | | +---------------------------------------+ Figure 1: PW termination The PW termination point receives untagged (also referred to as 'raw') or tagged ethernet frames and delivers them unaltered to the PW termination point on the remote LCCE. Hence it can provide untagged or tagged Ethernet link emulation service. The "NSP" function includes packet processing needed to translate the Ethernet packets that arrive at the CE-LCCE interface to/from the Ethernet packets that are applied to the PW termination point. Such functions may include stripping, overwriting or adding VLAN tags. The NSP functionality can be used in conjunction with local provisioning to provide heterogeneous services where the CE-LCCE encapsulations at the two ends may be different. The physical layer between the CE and LCCE, and any adaptation (NSP) functions between it and the PW termination, are outside of the scope of PWE3 and are not defined here. 2. PW Establishment With L2TPv3 as the tunneling protocol, Ethernet PWs are L2TPv3 sessions. A L2TP control connection has to be set up first between the two LCCEs. Individual PWs can then be established as L2TP sessions. 2.1. LCCE-LCCE Control Connection Establishment The two LCCEs that wish to set up Ethernet PWs MUST establish a L2TP control connection first as described in [L2TPv3]. Hence Ethernet PW type must be included in the Pseudo Wire Capabilities list. The type of PW can be either "Ethernet port" or "Ethernet VLAN". This indicates that the control connection can support the establishment of Ethernet PWs. Note that there are two Ethernet PW types required. This can be used for connecting Ethernet port to another Ethernet port; Ethernet VLAN to another Ethernet VLAN; or for providing heterogeneous connectivity using NSP processing. draft-ietf-l2tpext-pwe3-ethernet-00.txt [Page 3] Internet Draft draft-ietf-l2tpext-pwe3-ethernet-00.txt October 2002 2.2. PW Session Establishment The provisioning of an Ethernet port or Ethernet VLAN and its association with a PW triggers the establishment of an L2TP session as described in [L2TPv3]. The following are the signaling elements needed for the PW establishment: a) Pseudo Wire Type: The type of a Pseudo wire can be either "Ethernet port" or "Ethernet VLAN". Each LCCE signals its PW type in a AVP [L2TPv3] Attribute Type TBA. b) PW ID: Each PW is associated with a PW ID akin to the VC-ID in [PWE3-CRTL]. The two LCCEs of a PW have the same PW ID for it. The End Identifier AVP in L2TPv3 is used as the PW ID. The End Identifier AVP MUST be present in the ICRQ in order for the remote LCCE to determine the PW to associate the L2TP session with. An implementation MUST support an End Identifier of four octets known to both LCCEs either by manual configuration or some other means. Additional End Identifier formats which MAY be supported are outside the scope of this document. 2.3 PW Session Monitoring The working status of a PW is reflected by the state of the L2TPv3 session. If the corresponding L2TPv3 session is down, the PW associated with it MUST be shut down. The session keep-alive mechanism of L2TPv3 can serve as a link status monitoring mechanism for the PW (i.e. session). 2.3.1 SLI Message In addition to the session keep-alive mechanism of L2TPv3, Ethernet PW over L2TP makes use of the Set Link Info (SLI) control message defined in [L2TPv3]. The SLI message is used to signal Ethernet link status notifications between LCCEs. This can be useful to indicate the Ethernet interface state change without bringing down the L2TP session. The SLI message MUST be sent any time there is a status change of any values identified in the Circuit Status AVP. The only exception to this is the initial ICRQ, ICRP and CDN messages which establish and teardown the L2TP session itself. The SLI message may be sent from either LCCE at any time after the first ICRQ is sent (and perhaps before an ICRP is received, requiring the peer to perform a reverse Session ID lookup). Ether PW reports Circuit Status with the Circuit Status AVP defined in [L2TPv3]. For reference, this AVP is shown below: draft-ietf-l2tpext-pwe3-ethernet-00.txt [Page 4] Internet Draft draft-ietf-l2tpext-pwe3-ethernet-00.txt October 2002 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |A|N| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Value is a 16 bit mask with the two least significant bits defined and the remaining bits reserved for future use. Reserved bits MUST be set to 0 when sending, and ignored upon receipt. The A (Active) bit indicates whether the Ethernet interface is ACTIVE (1) or INACTIVE (0). The N (New) bit SHOULD be set to one (1) if this is the first time this interface has transitioned to ACTIVE, zero (0) otherwise. 3. Packet Processing 3.1. Encapsulation The encapsulation described in this section refers to the functionality performed by the PW termination point depicted in figure 1, unless otherwise indicated. The entire Ethernet frame without the preamble or FCS is encapsulated in L2TPv3 and is sent as a single packet by the ingress LCCE. This is done regardless of whether an 802.1Q tag is present in the Ethernet frame or not. For Ethernet port to port mode the remote LCCE simply decapsulates the L2TP payload and sends it out on the appropriate interface without modifying the Ethernet header. For Ethernet VLAN to VLAN, the remote LCCE MAY rewrite the VLAN tag. As described in section 1, the VLAN tag modification is a NSP function. The Ethernet PW over L2TP is homogeneous with respect to packet encapsulation i.e. both the ends of the PW are either untagged or tagged. The Ethernet PW can still be used to provide heterogeneous services using NSP functionality at the ingress and/or egress LCCE. The definition of such NSP functionality is outside the scope of this document. 3.2. Sequencing Data packet sequencing may be enabled for Ethernet PWs. The sequencing mechanims described in [L2TPv3] MUST be used for signaling sequencing support. draft-ietf-l2tpext-pwe3-ethernet-00.txt [Page 5] Internet Draft draft-ietf-l2tpext-pwe3-ethernet-00.txt October 2002 3.3. MTU Handling With L2TPv3 as the tunneling protocol, the packet resulted from the encapsulation is N bytes longer than Ethernet frame without the preamble or FCS, where N=8, L2TPv3 data messages are over IP; N=16, L2TPv3 data messages are over UDP; (N does not include the IP header). The fragmentation implications resulting from this are discussed in [PWE3-FRAG]. The mechanisms outlined in [PWE3-FRAG] SHOULD be followed with regards to handling fragmentation on an Ethernet PW over L2TPv3. 4. Security Considerations For generic security issues regarding PWs and Ethernet PWs, this document will eventually refer to documents from the PWE3 WG. L2TP-specific Security Considerations are TBD. 5. IANA Considerations The signaling mechanisms defined in this document rely upon the assignment of a Ethernet port mode and an Ethernet VLAN mode Pseudowire Type. IANA assignment of this value should take place within the PWE3 WG. 6. Acknowledgements This draft evolves from the draft, "Ethernet Pseudo Wire Emulation Edge-to-Edge". We would like to thank its authors, T.So, X.Xiao, L. Anderson, C. Flores, N. Tingle, S. Khandekar, D. Zelig and G. Heron for their contribution. We would also like to thank S. Nanji, the author of the draft, "Ethernet Service for Layer Two Tunneling Protocol", for writing the first ethernet over L2TP draft. 7. References [L2TPv3] J. Lau, M. Townsley, A. Valencia, G. Zorn, I. Goyret, G. Pall, A. Rubens, B. Palter, Layer Two Tunneling Protocol a.k.a. "L2TPv3," work in progress, draft-ietf-l2tpext-l2tp-base-03.txt [L2TP-IANA] Townsley, M., "L2TP IANA Considerations Update", Internet Draft, draft-ietf-l2tpext-rfc2661-iana-00.txt [PWE3-CRTL] L. Martini., et al., "Transport of Layer 2 Frames Over MPLS", draft-ietf-pwe3-control-protocol-00.txt draft-ietf-l2tpext-pwe3-ethernet-00.txt [Page 6] Internet Draft draft-ietf-l2tpext-pwe3-ethernet-00.txt October 200 [PWE3-FRAG] A. Malis, W. M. Townsley, "PWE3 Fragmentation and Reassembly", draft-malis-pwe3-fragmentation-00.txt [PWE3-LAYER] S. Bryant, L. Wood, M. Townsley, D. McPherson, "Protocol Layering in PWE3", draft-ietf-pwe3-protocol-layer-00.txt [PWE3-REQ] X. Xiao, D. McPherson, P. Pate, C. White, K. Kompella, V. Gill, T. D. Nadeau, "Requirements for Pseudo-Wire Emulation Edge-to-Edge", draft-ietf-pwe3-requirements-03.txt 8. Author Information Rahul Aggarwal Redback Networks 350 Holger Way San Jose, CA 95134 e-mail: rahul@redback.com XiPeng Xiao Redback Networks 300 Holger Way San Jose, CA 95134 e-mail: xipeng@redback.com W. Mark Townsley Cisco Systems 7025 Kit Creek Road PO Box 14987 Research Triangle Park, NC 27709 e-mail: mark@townsley.net Stewart Bryant Cisco Systems, 4, The Square, Stockley Park, Uxbridge UB11 1BL, United Kingdom. e-mail: stbryant@cisco.com Cheng-Yin Lee Alcatel 600 March Rd, Ottawa Ontario, Canada K2K 2E6 e-mail: Cheng-Yin.Lee@alcatel.com Tissa Senevirathne Consultant 1567 Belleville Way Sunnywale CA 94087 e-mail: tsenevir@hotmail.com draft-ietf-l2tpext-pwe3-ethernet-00.txt [Page 7] Internet Draft draft-ietf-l2tpext-pwe3-ethernet-00.txt October 200 Mitsuru Higashiyama Anritsu Corporation 1800 Onna, Atsugi-shi, Kanagawa-prf., 243-8555 Japan e-mail: Mitsuru.Higashiyama@yy.anritsu.co.jp draft-ietf-l2tpext-pwe3-ethernet-00.txt [Page 8]