Encapsulation Methods for Transport of Ethernet over MPLS Networks
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From: The IESG <email@example.com> To: IETF-Announce <firstname.lastname@example.org> Cc: Internet Architecture Board <email@example.com>, RFC Editor <firstname.lastname@example.org>, pwe3 mailing list <email@example.com>, pwe3 chair <firstname.lastname@example.org> Subject: Protocol Action: 'Encapsulation Methods for Transport of Ethernet Over MPLS Networks' to Proposed Standard The IESG has approved the following document: - 'Encapsulation Methods for Transport of Ethernet Over MPLS Networks ' <draft-ietf-pwe3-ethernet-encap-12.txt> as a Proposed Standard This document is the product of the Pseudowire Emulation Edge to Edge Working Group. The IESG contact persons are Mark Townsley and Jari Arkko. A URL of this Internet-Draft is: http://www.ietf.org/internet-drafts/draft-ietf-pwe3-ethernet-encap-12.txt
- Technical Summary This draft describes how an Ethernet Pseudowire (PW) is used to carry Ethernet/802.3 Protocol Data Units over an MPLS network. This enables service providers to offer "emulated" ethernet services over existing MPLS networks. This document specifies the encapsulation of Ethernet/802.3 PDUs within a pseudo wire. It also specifies the procedures for using a PW to provide a "point-to-point ethernet" service. - Working Group Summary This work has been thoroughly analysed by the working group and there is consensus for the design. A complementatry specification exists in L2TPext WG which describes how to carry an Ethernet PW over L2TPv3 over IP. - Protocol Quality This specification is well known in the industry and implementations exist. Note to RFC Editor At the end of Section 2, please add the following sentence: "Additional terminology relevant to pseudowires and Layer 2 Virtual Private Networking (L2VPN) in general may be found in [RFC4026]." Please replace the first three paragraphs of Section 4.6 with the following text: The Control Word defined in this section is based on the Generic PW MPLS Control Word as defined in [PWE3-CW]. It provides the ability to sequence individual frames on the PW, avoidance of equal-cost multiple-path load-balancing (ECMP) [RFC2992], and OAM mechanisms including VCCV [VCCV]. [PWE3-CW] states, "If a PW is sensitive to packet misordering and is being carried over an MPLS PSN that uses the contents of the MPLS payload to select the ECMP path, it MUST employ a mechanism which prevents packet misordering." This is necessary due to the fact that ECMP implementations may examine the first nibble after the MPLS label stack to determine whether the labelled packet is IP or not. Thus, if the source MAC address of an ethernet frame carried over the PW without a control word present begins with 0x4 or 0x6, it could be mistaken for an IPv4 or IPv6 packet. This could, depending on the configuration and topology of the MPLS network, lead to a situation where all packets for a given PW do not follow the same path. This may increase out-of-order frames on a given PW, or cause OAM packets to follow a different path than actual traffic (see section 4.4.3 on Frame Ordering). The features that the control word provides may not be needed for a given ethernet PW. For example, ECMP may not be present or active on a given MPLS network, strict frame sequencing may not be required, etc. If this is the case, the control word provides little value and is therefore optional. Early ethernet PW implementations have been deployed that do not include a control word or the ability to process one if present. To aid in backwards compatibility, future implementations MUST be able to send and receive frames without the control word present. In all cases the ingress PE MUST be aware of whether the egress PE will send a control word over a specific PW. This may be achieved by configuration of the PEs, or by signaling, as defined in [PWE3-CTRL]. Additional Informational References: [VCCV] T. D. Nadeau, R. Aggarwal, "Pseudo Wire Virtual Circuit Connectivity Verification (VCCV)", draft-ietf-pwe3-vccv-07.txt, August 2005. (work in progress) [RFC2992] RFC-2992: Analysis of an Equal-Cost Multi-Path Algorithm, C. Hopps, November 2000 [RFC4026] Andersson, L., Madsen, T. "Provider Provisioned Virtual Private Network (VPN) Terminology", RFC 4026, March 2005.