Network Working Group Rahul Aggarwal Internet Draft Juniper Networks Expiration Date: April 2006 W. Mark Townsley Maria A. Dos Santos Cisco Systems Editors October 2005 Transport of Ethernet Frames over L2TPv3 draft-ietf-l2tpext-pwe3-ethernet-05.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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/1id-abstracts.html 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. Aggarwal, Townsley, et al. Standards Track [Page 1] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 Contributors Following is the complete list of contributors to this document. Rahul Aggarwal Juniper Networks Xipeng Xiao Riverstone Networks W. Mark Townsley Stewart Bryant Maria Alice Dos Santos Cisco Systems Cheng-Yin Lee Alcatel Tissa Senevirathne Consultant Mitsuru Higashiyama Anritsu Corporation Table of Contents Status of this Memo.......................................... 1 1. Introduction.............................................. 3 1.1 Abbreviations......................................... 3 1.2 Requirements.......................................... 3 2. PW Establishment.......................................... 4 2.1 LCCE-LCCE Control Connection Establishment............ 4 2.2 PW Session Establishment.............................. 5 2.3 PW Session Monitoring................................. 5 3. Packet Processing......................................... 7 3.1 Encapsulation......................................... 7 3.2 Sequencing............................................ 7 3.3 MTU Handling.......................................... 7 4. Applicability Statement................................... 8 5. Security Considerations................................... 9 6. IANA Considerations....................................... 9 7. Acknowledgements.......................................... 10 8. References................................................ 10 8.1 Normative References.................................. 10 Aggarwal, Townsley, et al. Standards Track [Page 2] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 8.2 Informative References................................ 10 9. Author Information........................................ 10 Specification of Requirements In this document, several words are used to signify the requirements of the specification. These words are often capitalized. 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]. 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 [RFC3931]. 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 [RFC3931]) 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 [RFC3985]. 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. Aggarwal, Townsley, et al. Standards Track [Page 3] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 +---------------------------------------+ | 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 [RFC3931]. Hence an Ethernet PW type must be included in the Pseudo Wire Capabilities List as defined in [RFC3931]. 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 Aggarwal, Townsley, et al. Standards Track [Page 4] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 connecting an 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 [RFC3931]. 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 [RFC3931]. 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 [RFC3931] 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 [RFC3931] 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. Aggarwal, Townsley, et al. Standards Track [Page 5] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 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 [RFC3931]. 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 [RFC3931]. 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. Aggarwal, Townsley, et al. Standards Track [Page 6] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 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 [RFC3931] 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; Aggarwal, Townsley, et al. Standards Track [Page 7] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 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 [RFC3931]. 4. Applicability Statement The Ethernet PW emulation allows a service provider to offer a "port to port" Ethernet based service across an IP packet switched network (PSN) while the Ethernet VLAN PW emulation allows an "Ethernet VLAN to VLAN" based service across an IP packet switched network (PSN). The Ethernet or Ethernet VLAN PW emulation has the following characteristics in relationship to the respective native service: o Ethernet PW connects two Ethernet ACs while Ethernet VLAN PW connects two Ethernet VLAN ACs, supporting bi-directional transport of variable length Ethernet frames. The ingress LCCE strips the preamble and FCS from the Ethernet frame and transports the frame in its entirety across the PW. This is done regardless of the presence of the 802.1Q tag in the frame. The egress LCCE receives the Ethernet frame from the PW and regenerates the preamble or FCS before forwarding the frame to the attached Remote System (See Section 3.1). Since FCS is not being transported across either Ethernet or Ethernet VLAN PWs, payload integrity transparency may be lost. To achieve payload integrity transparency on Ethernet or Ethernet VLAN PWs using L2TP over IP or L2TP over UDP/IP, the L2TPv3 session can utilize IPSec as specified in Section 4.1.3 of [RFC3931]. o For Ethernet VLAN PW, VLAN tag rewrite can be achieved by NSP at the egress LCCE which is outside the scope of this document (See Section 3.1). o The Ethernet or Ethernet VLAN PW only supports homogeneous Ethernet frame type across the PW; both ends of the PW must be either tagged or untagged. Heterogeneous frame type support achieved with NSP functionality is outside the scope of this document (See Section 3.1). o Ethernet port or Ethernet VLAN status notification is provided using the Circuit Status AVP in SLI message (See Section 2.3.1). Loss of connectivity between LCCEs can be detected by the L2TPv3 keepalive mechanism (see Section 2.3.1 in [RFC3931]). The LCCE can convey these indications back to its attached Remote System. Aggarwal, Townsley, et al. Standards Track [Page 8] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 o The maximum frame size that can be supported is limited by the PSN MTU minus the L2TPv3 header size, unless fragmentation and reassembly is used (see Section 3.3 and Section 4.1.4 of [RFC3931]). o The packet switched network may reorder, duplicate, or silently drop packets. Sequencing may be enabled in the Ethernet or Ethernet VLAN PW for some or all packets to detect lost, duplicate, or out-of-order packets on a per-session basis (see Section 3.2). o The faithfulness of an Ethernet or Ethernet VLAN PW may be increased by leveraging Quality of Service features of the LCCEs and the underlying PSN. For example for Ethernet VLAN transport, the ingress LCCE MAY consider the user priority field of the VLAN tag for traffic classification and QoS treatments, such as determining the TOS octet (for example, according to DSCP) of the encapsulating IP header. Similarly, the egress LCCE MAY consider the TOS octet of the encapsulating IP header when rewriting the user priority field of the VLAN tag or queueing the Ethernet frame before forwarding the frame to the Remote System. The mapping between the 802.1Q COS and the IP header Qos field and the Quality of Service model deployed are application specific and are outside the scope of this document. 5. Security Considerations Ethernet over L2TPv3 is subject to all of the general security considerations outlined in [RFC3931]. 6. 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 [RFC3931] and L2TPv3 Pseudowire Types in 10.6 of [RFC3931]) by the IANA (number space created as part of publication of [RFC3931]): Pseudowire Types ---------------- 0x0004 Ethernet VLAN Pseudowire Type 0x0005 Ethernet Pseudowire Type Aggarwal, Townsley, et al. Standards Track [Page 9] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 7. 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. Thanks to Carlos Pignataro for providing a thorough review and helpful input. 8. References 8.1 Normative References [RFC3931] J. Lau, M. Townsley, I. Goyret, "Layer Two Tunneling Protocol (Version 3)", RFC3931, March 2005. 8.2 Informative References [RFC3985] S. Bryant, P. Pate, "Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture", RFC3985, March 2005 9. Author Information Rahul Aggarwal Juniper Networks 1194 North Mathilda Avenue Sunnyvale, CA 94089 e-mail: rahul@juniper.net XiPeng Xiao Riverstone Networks 5200 Great America Parkway Santa Clara, CA 95054 Email: xxiao@riverstonenet.com W. Mark Townsley Cisco Systems 7025 Kit Creek Road PO Box 14987 Research Triangle Park, NC 27709 Aggarwal, Townsley, et al. Standards Track [Page 10] INTERNET DRAFT draft-ietf-l2tpext-pwe3-ethernet-05.txt October 2005 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 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: mariados@cisco.com 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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