RFC 4003

GMPLS Signaling Procedure for Egress Control

📅 published February 2005, from ietf

RFC 4003: GMPLS Signaling Procedure for Egress Control 🎀

okay bestie, let's get into this one ✨ It's RFC 4003, "GMPLS Signaling Procedure for Egress Control," by Lou Berger of Movaz Networks, dated February 2005. It's a Standards Track doc, and it Updates RFC 3473 (it doesn't obsolete anything) 💅 Network Working Group energy, fr fr.

Status of This Memo 📜

this one is an Internet standards track protocol for the Internet community, and it's asking everyone for discussion and suggestions for improvements 🫶 check the current edition of the "Internet Official Protocol Standards" (STD 1) for where this protocol stands on standardization and status. distribution is unlimited, so share it with your whole group chat 💜

Copyright Notice ©️

Abstract 🦋

this doc clarifies how we control the label used on the output/downstream interface of the egress node of a Label Switched Path (LSP), aka "Egress Control" 👑 Egress Control is already implicit in Generalized Multi-Protocol Label Switching (GMPLS) Signaling. this doc just clarifies how GMPLS Signaling is specified, and it does not change any GMPLS signaling mechanisms or procedures. no drama, just clarity ✨

1. Background 🧚

the ability to control the label on the output/downstream interface of an egress node was one of the early GMPLS requirements 💖 back in the early GMPLS docs this was called "Egress Control". as the GMPLS docs grew up, controlling a label on an egress interface got generalized to controlling a label on any interface. you can see that glow-up in Section 6 of [RFC3471] and Section 5.1 of [RFC3473] 🌈 when that happened, the egress control procedures got generalized too. the result was meant to cover egress control, but that intention isn't clear to everyone, so this note restates the procedures for controlling a label used on an egress output/downstream interface. it's giving clarity 🔥

for context, here's the text from the GMPLS signalling document dated June 2000 about ERO (Explicit Route Object) for egress control:

   6. Egress Control

   The LSR at the head-end of an LSP can control the termination of
   the LSP by using the ERO.  To terminate an LSP on a particular
   outgoing interface of the egress LSR, the head-end may specify the
   IP address of that interface as the last element in the ERO,
   provided that interface has an associated IP address.

   There are cases where the use of IP address doesn't provide enough
   information to uniquely identify the egress termination.  One case
   is when the outgoing interface on the egress LSR is a component
   link of a link bundle.  Another case is when it is desirable to
   "splice" two LSPs together, i.e., where the tail of the first LSP
   would be "spliced" into the head of the second LSP.  This last
   case is more likely to be used in the non-PSC classes of links.

   6.2. Procedures

   The Egress Label subobject may appear only as the last subobject
   in the ERO/ER.  Appearance of this subobject anywhere else in the
   ERO/ER is treated as a "Bad strict node" error.

   During an LSP setup, when a node processing the ERO/RR performs
   Next Hop selection finds that the second subobject is an Egress
   Label Subobject, the node uses the information carried in this
   subobject to determine the handling of the data received over that
   LSP.  Specifically, if the Link ID field of the subobject is non
   zero, then this field identifies a specific (outgoing) link of the
   node that should be used for sending all the data received over
   the LSP.  If the Label field of the subobject is not Implicit NULL
   label, this field specifies the label that should be used as an
   outgoing label on the data received over the LSP.

   Procedures by which an LSR at the head-end of an LSP obtains the
   information needed to construct the Egress Label subobject are
   outside the scope of this document.

2. Egress Control Procedures 💅

this section is meant to go alongside Sections 5.1.1 and 5.2.1 of [RFC3473] 🫶 those procedures aren't being changed at all. this section just clarifies the procedures for the label used on an egress output/downstream interface.

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]. 📚

2.1. ERO Procedures 🌸

Egress Control happens when the node processing an ERO is the egress and the ERO contains one or more subobjects related to the output/downstream interface 💖 in that case, the outgoing/downstream interface shows up in the ERO as the last listed local interface. an interface can be numbered or unnumbered, and both are fine 🦋

to support Egress Control, an egress checks whether the received ERO contains an outgoing/downstream interface. if it does, it looks at the subobject or subobjects after the interface. for a unidirectional LSP, one subobject gets examined. for bidirectional LSPs, two subobjects get examined ✨ if the U-bit of the subobject being examined is clear (0), then the value of the label MUST be used for transmitting traffic associated with the LSP on the indicated outgoing/downstream interface 🔥

if the U-bit of the subobject being examined is set (1), then the label value is used for upstream traffic associated with the bidirectional LSP. specifically, the label value gets used for the traffic associated with the LSP that will be received on the indicated outgoing/downstream interface 🌈

per [RFC3473], any errors found while processing the ERO, including when the listed label(s) aren't acceptable or can't be supported in forwarding, SHOULD result in the generation of a PathErr message with the error code "Routing Error" and error value of "Bad Explicit Route Object" 🙈

2.2. RRO Procedures 🍓

if an ERO is used to specify outgoing interface information at the egress, and label recording is indicated for the LSP, the egress should include the specified interface information and the specified label or labels in the corresponding RRO (Route Record Object) 🧚

3. Security Considerations 💀

this doc clarifies procedures defined in [RFC3473] but doesn't define any new procedures 😭 so no new security considerations are introduced. phew, you're safe bestie 🫶

4. Acknowledgments 💜

thanks to Adrian Farrel, Alan Kullberg, and Dimitri Papadimitriou for the valuable comments and input 🌟

5. Normative References 📖

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
             (GMPLS) Signaling Functional Description", RFC 3471,
             January 2003.

   [RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching
             (GMPLS) Signaling Resource ReserVation Protocol-Traffic
             Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.

Author's Address 🏡

   Lou Berger
   Movaz Networks, Inc.
   7926 Jones Branch Drive
   Suite 615
   McLean VA, 22102

   Phone:  +1 703 847-1801
   EMail:  lberger@movaz.com

Full Copyright Statement 🌈

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Acknowledgement 🌷

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📦 where this page comes from

ietf: rfc4003 2005-02
💖 girlified by claude-haiku-5-5 on 2026-10-16: a language model's rewrite of the original, under its terms