Network Working Group Rahul Aggarwal Internet Draft Juniper Networks Expiration Date: April 2005 W. Mark Townsley Maria A. Dos Santos Cisco Systems Editors Transport of Ethernet Frames over L2TPv3 draft-ietf-l2tpext-pwe3-ethernet-02.txt Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. 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. 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 RFC-2119 [KEYWORDS]. Contributors Following is the complete list of contributors to this document. Rahul Aggarwal Juniper Networks Xipeng Xiao Riverstone Networks W. Mark Townsley Stewart Bryant Cisco Systems Cheng-Yin Lee Alcatel Tissa Senevirathne Consultant Mitsuru Higashiyama Anritsu Corporation Table of Contents 1 Introduction........................................ 3 1.1 Abbreviations....................................... 3 1.2 Requirements........................................ 3 2 PW Establishment.................................... 3 2.1 LCCE-LCCE Control Connection Establishment.......... 4 2.2 PW Session Establishment............................ 4 2.3 PW Session Monitoring............................... 4 2.3.1 SLI Message......................................... 5 3 Packet Processing................................... 6 3.1 Encapsulation....................................... 6 3.2 Sequencing.......................................... 6 3.3 MTU Handling........................................ 6 4 Security Considerations............................. 7 5 IANA Considerations................................. 7 6 Acknowledgements.................................... 7 7 References.......................................... 7 7.1 Normative References................................ 7 7.2 Informative References.............................. 7 8 Author Information.................................. 8 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 L2TPv3 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-ARCH]. The Ethernet interface may be connected to one or more Remote Systems (an L2TPv3 Remote System is referred to as Customer Edge (CE) in this and associated PWE3 documents). The LCCE may or may not be a PE. +---------------------------------------+ | LCCE | +-+ +-----+ +------+ +------+ +-+ |P| | | |PW ter| | PSN | |P| Ethernet <==>|h|<=>| NSP |<=>|minati|<=>|Tunnel|<=>|h|<==> PSN Interface |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. An 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 an Ethernet PW type must be included in the Pseudo Wire Capabilities List as defined in [L2TPv3]. 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. For connecting an Ethernet port to another Ethernet port, the PW Type MUST be "Ethernet port"; for connecting Ethernet VLAN to another Ethernet VLAN, the PW Type MUST be "Ethernet VLAN. 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 Pseudo Wire type in the Pseudowire Type AVP [L2TPv3]. The assigned values for "Ethernet port" and "Ethernet VLAN" Pseudo Wire types are captured in the "IANA Considerations" of this document. The Pseudowire Type AVP MUST be present in the ICRQ. b) Pseudo Wire ID: Each PW is associated with a Pseudo Wire ID. The two LCCEs of a PW have the same Pseudo Wire ID for it. The Remote End Identifier AVP [L2TPv3] is used to convey the Pseudo Wire ID. The Remote 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 a Remote End Identifier of four octets known to both LCCEs either by manual configuration or some other means. Additional Remote End Identifier formats which MAY be supported are outside the scope of this document. c) The Circuit Status AVP [L2TPv3] MUST be included in ICRQ and ICRP to indicate the circuit status of the Ethernet port or Ethernet VLAN. The N (New) bit of the Circuit Status AVP in ICRQ and ICRP MUST be set to 1 indicating that the status is for a new circuit while the A (Active) bit is set to 0 (INACTIVE) or 1 (ACTIVE) to reflect the circuit operational status. Subsequent circuit status change of the Ethernet port or Ethernet VLAN MUST be conveyed in the Circuit Status AVP in ICCN or SLI control messages. In ICCN and SLI, the Circuit Status AVP N bit MUST be set to 0 indicating that the status is for an existing circuit. The A bit should be set to 0 or 1 to reflect the circuit operational status at that point in time. 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 control connection keep- alive mechanism of L2TPv3 can serve as a link status monitoring mechanism for the set of PWs associated with a Control Connection. 2.3.1. SLI Message In addition to the control connection 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. Note that change in the Ethernet interface state will trigger a SLI message for each PW associated with that Ethernet interface. This may be one Ethernet Port PW or more than one Ethernet VLAN PW. 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). Ethernet PW reports Circuit Status with the Circuit Status AVP defined in [L2TPv3]. For reference, this AVP is shown below: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved |N|A| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 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 the circuit status indication is for a new Ethernet circuit, 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 an 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 mechanisms described in [L2TPv3] MUST be used for signaling sequencing support. 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. The value of N depends on the following fields: L2TP Session Header: Flags, Ver, Res - 4 octets (L2TPv3 over UDP only) Session ID - 4 octets Cookie Size - 0, 4 or 8 octets L2-Specific Sublayer - 0 or 4 octets (i.e., using sequencing) Hence the range for N in octets is: N = 4-16, for L2TPv3 data messages over IP; N = 16-28, for L2TPv3 data messages over UDP; (N does not include the IP header). The MTU and fragmentation implications resulting from this are discussed in section 4.1.4 of [L2TPv3]. 4. Security Considerations Ethernet over L2TPv3 is subject to all of the general security considerations outlined in [L2TPv3]. 5. IANA Considerations The signaling mechanisms defined in this document rely upon the allocation of following Ethernet Pseudowire Types (see Pseudo Wire Capabilities List as defined in 5.4.3 of [L2TPv3] and L2TPv3 Pseudowire Types in 10.6 of [L2TPv3]) by the IANA (number space created as part of publication of [L2TPv3]): Pseudowire Types ---------------- 0x0004 Ethernet VLAN Pseudowire Type 0x0005 Ethernet Pseudowire Type 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 7.1. Normative 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-14.txt 7.2. Informative References [PWE3-ARCH] Stewart Bryant, Prayson Pate, "PWE3 Architecture", draft-ietf-pwe3-arch-07.txt 8. Author Information Rahul Aggarwal Juniper Networks 1194 North Mathilda Avenue Sunnyvale, CA 94089 e-mail: email@example.com XiPeng Xiao Riverstone Networks 5200 Great America Parkway Santa Clara, CA 95054 Email: firstname.lastname@example.org W. Mark Townsley Cisco Systems 7025 Kit Creek Road PO Box 14987 Research Triangle Park, NC 27709 e-mail: email@example.com Stewart Bryant Cisco Systems, 4, The Square, Stockley Park, Uxbridge UB11 1BL, United Kingdom. e-mail: firstname.lastname@example.org 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: email@example.com Mitsuru Higashiyama Anritsu Corporation 1800 Onna, Atsugi-shi, Kanagawa-prf., 243-8555 Japan e-mail: Mitsuru.Higashiyama@yy.anritsu.co.jp Maria Alice Dos Santos Cisco Systems 170 W Tasman Dr San Jose, CA 95134 e-mail: firstname.lastname@example.org Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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