Internet-Draft | Multiple GAL | April 2021 |
Mirsky, et al. | Expires 30 October 2021 | [Page] |
- Workgroup:
- MPLS Working Group
- Internet-Draft:
- draft-many-mpls-multiple-gal-00
- Updates:
- 5586 (if approved)
- Published:
- Intended Status:
- Standards Track
- Expires:
Number of Generic Associated Channel Labels in the MPLS Label Stack
Abstract
This document describes the requirements for using multiple Generic Associated Channel Labels (GALs) in an MPLS label stack. As a result, the document updates RFC 5586 by removing the restriction imposed on the usage of GAL that limits the number of GAL in the MPLS label stack to one.¶
Status of This Memo
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.¶
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.¶
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."¶
This Internet-Draft will expire on 30 October 2021.¶
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶
1. Introduction
[RFC5085] defined the associated channel mechanism and the Associated Channel Header (ACH) for exchange of control, management, and Operations, Administration, and Maintenance (OAM) messages in Pseudowires (PWs). [RFC5586] generalized that associated channel mechanism and the ACH for use in Sections, Label Switched Paths (LSPs), and PWs as the Generic Associated Channel (G-ACh) and introduced the generalized label-based exception mechanism using the Generic Associated Channel Label (GAL).¶
[RFC5586] restricted the number of GALs present in the MPLS label stack to not more than one appearance. This document updates [RFC5586] by removing that restriction for non-MPLS-TP networks.¶
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
3. Number of GAL in the MPLS Label Stack
[RFC5586] has limited the number of GALs in an MPLS label stack:¶
- Furthermore, when present, the GAL MUST NOT appear more than once in the label stack.¶
In some MPLS networks, e.g., when realizing Service Function Chaining with MPLS-based forwarding plane [RFC8595], putting more than a single GAL in the MPLS label stack can simplify the processing of OAM packets and, as a result, improve the performance. An extension of the MPLS Echo Request and Reply protocol [RFC8029] in such an environment is discussed in [I-D.lm-mpls-sfc-path-verification]. Because it is expected that a general Service Function does not support processing of MPLS echo request messages, a GAL being used within a basic unit of MPLS label stack to indicate that the payload is ACH-encapsulated OAM message. And in the label-stacking case, multiple basic units on the MPLS label stack, and, consequently, GALs could be placed in an MPLS label stack. Thus, this document removes the limit on the number of GALs present in an MPLS label stack by changing the statement in [RFC5586] as follows:¶
- Furthermore, in non-MPLS-TP networks, when present, the GAL MAY appear more than once in the label stack.¶
[RFC5586] requires that when GAL is at the bottom of the label stack, it is followed by an ACH:¶
- Where the GAL is at the bottom of the label stack (i.e., S bit set to 1), then it MUST always be followed by an ACH.¶
This document updates [RFC5586] by extending that requirement for environments when GAL is not at the bottom of the label stack as follows:¶
- Where GAL is present in the label stack, the label element at the bottom of the label stack (i.e., S bit set to 1) MUST always be followed by an ACH.¶
4. Processing GAL when not at the Bottom of the Label Stack
[Ed.note: Describe GAL processing by transit and egress nodes. Illustrate the transformation of the MPLS label stack as a packet transits through the domain.]¶
5. IANA Considerations
This document has no requests for IANA, and this section can be removed before the publication.¶
6. Security Considerations
There are no further security considerations than those in [RFC5586].¶
7. Acknowledgments
TBA¶
8. References
8.1. Normative References
- [RFC2119]
- Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
- [RFC5085]
- Nadeau, T., Ed. and C. Pignataro, Ed., "Pseudowire Virtual Circuit Connectivity Verification (VCCV): A Control Channel for Pseudowires", RFC 5085, DOI 10.17487/RFC5085, , <https://www.rfc-editor.org/info/rfc5085>.
- [RFC5586]
- Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., "MPLS Generic Associated Channel", RFC 5586, DOI 10.17487/RFC5586, , <https://www.rfc-editor.org/info/rfc5586>.
- [RFC8174]
- Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
- [RFC8595]
- Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based Forwarding Plane for Service Function Chaining", RFC 8595, DOI 10.17487/RFC8595, , <https://www.rfc-editor.org/info/rfc8595>.
8.2. Informative References
- [I-D.lm-mpls-sfc-path-verification]
- Yao, L. and G. Mirsky, "MPLS-based Service Function Path(SFP) Consistency Verification", Work in Progress, Internet-Draft, draft-lm-mpls-sfc-path-verification-02, , <https://tools.ietf.org/html/draft-lm-mpls-sfc-path-verification-02>.
- [RFC8029]
- Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., Aldrin, S., and M. Chen, "Detecting Multiprotocol Label Switched (MPLS) Data-Plane Failures", RFC 8029, DOI 10.17487/RFC8029, , <https://www.rfc-editor.org/info/rfc8029>.