Time To Live (TTL) Processing in Multi-Protocol Label Switching (MPLS) Networks
RFC 3443
Document | Type |
RFC - Proposed Standard
(January 2003; No errata)
Updated by RFC 5462
Updates RFC 3032
Was draft-ietf-mpls-ttl (mpls WG)
|
|
---|---|---|---|
Authors | Bora Akyol , Puneet Agarwal | ||
Last updated | 2015-10-14 | ||
Replaces | draft-agarwal-mpls-ttl | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | WG Document | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 3443 (Proposed Standard) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Scott Bradner | ||
Send notices to | (None) |
Network Working Group P. Agarwal Request for Comments: 3443 Brocade Updates: 3032 B. Akyol Category: Standards Track Cisco Systems January 2003 Time To Live (TTL) Processing in Multi-Protocol Label Switching (MPLS) Networks Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document describes Time To Live (TTL) processing in hierarchical Multi-Protocol Label Switching (MPLS) networks and is motivated by the need to formalize a TTL-transparent mode of operation for an MPLS label-switched path. It updates RFC 3032, "MPLS Label Stack Encoding". TTL processing in both Pipe and Uniform Model hierarchical tunnels are specified with examples for both "push" and "pop" cases. The document also complements RFC 3270, "MPLS Support of Differentiated Services" and ties together the terminology introduced in that document with TTL processing in hierarchical MPLS networks. 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]. 1. Introduction and Motivation This document describes Time To Live (TTL) processing in hierarchical MPLS networks. We believe that this document adds details that have not been addressed in [MPLS-ARCH, MPLS-ENCAPS], and that the methods presented in this document complement [MPLS-DS]. Agarwal & Akyol Standards Track [Page 1] RFC 3443 TTL Processing in MPLS Networks January 2003 In particular, a new mode of operation (referred to as the Pipe Model) is introduced to support the practice of configuring MPLS LSPs such that packets transiting the LSP see the tunnel as a single hop regardless of the number of intermediary label switch routers (LSR). The Pipe Model for TTL is currently being used in multiple networks and is provided as an option configurable by the network operator by several vendors. This document formalizes the TTL processing in MPLS networks and ties it with the terminology introduced in [MPLS-DS]. 2. TTL Processing in MPLS Networks 2.1. Changes to RFC 3032 [MPLS-ENCAPS] a) [MPLS-ENCAPS] only covers the Uniform Model and does NOT address the Pipe Model or the Short Pipe Model. This document addresses these two models and for completeness will also address the Uniform Model. b) [MPLS-ENCAPS] does not cover hierarchical LSPs. This document addresses this issue. c) [MPLS-ENCAPS] does not define TTL processing in the presence of Penultimate Hop Popping (PHP). This document addresses this issue. 2.2. Terminology and Background As defined in [MPLS-ENCAPS], MPLS packets use a MPLS shim header that indicates the following information about a packet: a) MPLS Label (20 bits) b) TTL (8 bits) c) Bottom of stack (1 bit) d) Experimental bits (3 bits) The experimental bits were later redefined in [MPLS-DS] to indicate the scheduling and shaping behavior that could be associated with an MPLS packet. [MPLS-DS] also defined two models for MPLS tunnel operation: Pipe and Uniform Models. In the Pipe Model, a MPLS network acts like a circuit when MPLS packets traverse the network such that only the LSP ingress and egress points are visible to nodes that are outside the tunnel. A Short variation of the Pipe Model is also defined in [MPLS-DS] to differentiate between different egress forwarding and QoS treatments. On the other hand, the Uniform Model makes all the Agarwal & Akyol Standards Track [Page 2] RFC 3443 TTL Processing in MPLS Networks January 2003 nodes that a LSP traverses visible to nodes outside the tunnel. We will extend the Pipe and Uniform Models to include TTL processing in the following sections. Furthermore, TTL processing, when performing PHP, is also described in this document. For a detailed description of Pipe and Uniform Models, please see [MPLS-DS]. TTL processing in MPLS networks can be broken down into two logical blocks: (i) the incoming TTL determination to take into account any tunnel egress due to MPLS Pop operations; (ii) packet processing ofShow full document text