Encapsulation Methods for Transport of Layer 2 Frames over MPLS Networks
RFC 4905
Document | Type |
RFC - Historic
(June 2007; No errata)
Was draft-martini-l2circuit-encap-mpls (individual in int area)
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Authors | Nasser El-Aawar , Luca Martini , Eric Rosen | ||
Last updated | 2020-07-29 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 4905 (Historic) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Mark Townsley | ||
Send notices to | (None) |
Network Working Group L. Martini, Ed. Request for Comments: 4905 E. Rosen, Ed. Category: Historic Cisco Systems, Inc. N. El-Aawar, Ed. Level 3 Communications, LLC June 2007 Encapsulation Methods for Transport of Layer 2 Frames over MPLS Networks Status of This Memo This memo defines a Historic Document for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document describes methods for encapsulating the Protocol Data Units (PDUs) of layer 2 protocols such as Frame Relay, Asynchronous Transfer Mode (ATM), or Ethernet for transport across an MPLS network. This document describes the so-called "draft-martini" protocol, which has since been superseded by the Pseudowire Emulation Edge to Edge Working Group specifications described in RFC 4447 and related documents. Martini, et al. Historic [Page 1] RFC 4905 Encapsulation for L2 Frames over MPLS June 2007 Table of Contents 1. Introduction ....................................................3 2. Specification of Requirements ...................................3 3. Special Note ....................................................4 4. General Encapsulation Method ....................................4 4.1. The Control Word ...........................................4 4.1.1. Setting the Sequence Number .........................5 4.1.2. Processing the Sequence Number ......................6 4.2. MTU Requirements ...........................................6 5. Protocol-Specific Details .......................................7 5.1. Frame Relay ................................................7 5.2. ATM ........................................................8 5.2.1. ATM AAL5 CPCS-SDU Mode ..............................9 5.2.2. ATM Cell Mode ......................................10 5.2.3. OAM Cell Support ...................................12 5.2.4. CLP bit to Quality of Service Mapping ..............12 5.3. Ethernet VLAN .............................................12 5.4. Ethernet ..................................................12 5.5. High-Level Data Link Control (HDLC) .......................13 5.6. PPP .......................................................13 6. Using an MPLS Label as the Demultiplexer Field .................13 6.1. MPLS Shim EXP Bit Values ..................................14 6.2. MPLS Shim S Bit Value .....................................14 6.3. MPLS Shim TTL Values ......................................14 7. Security Considerations ........................................14 8. Normative References ...........................................14 9. Informative References .........................................16 10. Co-Authors ....................................................16 Martini, et al. Historic [Page 2] RFC 4905 Encapsulation for L2 Frames over MPLS June 2007 1. Introduction In an MPLS network, it is possible to use control protocols such as those specified in [RFC4906] to set up "emulated virtual circuits" that carry the Protocol Data Units of layer 2 protocols across the network. A number of these emulated virtual circuits (VCs) may be carried in a single tunnel. This requires, of course, that the layer 2 PDUs be encapsulated. We can distinguish three layers of this encapsulation: - the "tunnel header", which contains the information needed to transport the PDU across the MPLS network; this header belongs to the tunneling protocol, e.g., MPLS, Generic Routing Encapsulation (GRE), and Layer 2 Tunneling Protocol (L2TP). - the "demultiplexer field", which is used to distinguish individual emulated virtual circuits within a single tunnel; this field must be understood by the tunneling protocol as well; it may be, e.g., an MPLS label or a GRE key field. - the "emulated VC encapsulation", which contains the information about the enclosed layer 2 PDU that is necessary in order to properly emulate the corresponding layer 2 protocol. This document specifies the emulated VC encapsulation for a number of layer 2 protocols. Although different layer 2 protocols require different information to be carried in this encapsulation, an attemptShow full document text