Stateless MNA-based Egress Protection (SMEP)
draft-ihle-mpls-mna-stateless-egress-protection-01
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Fabian Ihle , Michael Menth | ||
| Last updated | 2025-06-13 | ||
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| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
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draft-ihle-mpls-mna-stateless-egress-protection-01
Multiprotocol Label Switching F. Ihle
Internet-Draft M. Menth
Intended status: Standards Track University of Tuebingen
Expires: 15 December 2025 13 June 2025
Stateless MNA-based Egress Protection (SMEP)
draft-ihle-mpls-mna-stateless-egress-protection-01
Abstract
The MPLS Egress Protection Framework specifies a fast reroute
framework for protecting IP/MPLS services. To that end, bypass
tunnels have to be signaled to the Point of Local Repair (PLR).
Further, the PLR must maintain the bypass forwarding state on a per-
transport-tunnel basis. This document presents the concept of
Stateless MNA-based Egress Protection (SMEP). SMEP protects egress
routers by providing alternative MPLS egress labels in-stack. This
mechanism does not require a bypass forwarding state in PLRs. An
example for the application of SMEP is given using a MPLS network
action for stack management.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://uni-tue-
kn.github.io/mpls-mna-stateless-egress-protection/draft-ihle-mpls-
mna-stateless-egress-protection.html. Status information for this
document may be found at https://datatracker.ietf.org/doc/draft-ihle-
mpls-mna-stateless-egress-protection/.
Discussion of this document takes place on the Multiprotocol Label
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Subscribe at https://www.ietf.org/mailman/listinfo/mpls/.
Source for this draft and an issue tracker can be found at
https://github.com/uni-tue-kn/mpls-mna-stateless-egress-protection.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1. Abbreviations . . . . . . . . . . . . . . . . . . . . 3
2. Concept of SMEP . . . . . . . . . . . . . . . . . . . . . . . 4
3. Stack Management with POP-N-LSE Operation Network Action for
SMEP . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
The MPLS egress protection framework in [RFC8679] establishes bypass
tunnels for egress routers on an egress failure, i.e., on a node or a
link failure. This is referred to as egress protection. The
protection mechanism relies on a Point of Local Repair (PLR) to
perform local failure detection and local repair. Typically, this
PLR is the penultimate router. When an egress failure occurs,
packets are rerouted to an alternative egress router. The PLR node
maintains the bypass forwarding state, which is a mapping of specific
labels to bypass tunnels. The bypass tunnels are signaled using
existing mechanisms, i.e., via an IGP, or topology-driven label
distribution protocols such as LDP.
This document defines the concept of Stateless MNA-based Egress
Protection (SMEP). SMEP provides an alternative to the rerouting
mechanism defined for the PLR, allowing the PLR to be stateless.
1.1. Terminology
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.
1.1.1. Abbreviations
This document makes use of the terms defined in [RFC8679] and in
[I-D.ietf-mpls-mna-hdr].
Further abbreviations used in this document:
+==============+=====================+===============+
| Abbreviation | Meaning | Reference |
+==============+=====================+===============+
| BML | Bypass MPLS Label | This document |
+--------------+---------------------+---------------+
| SMEP | Stateless MNA-based | This document |
| | Egress Protection | |
+--------------+---------------------+---------------+
Table 1: Abbreviations.
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2. Concept of SMEP
With SMEP, the egress bypass tunnel is indicated by one or multiple
alternative MPLS forwarding labels which are located at the bottom of
stack. We call those labels Bypass MPLS Labels (BMLs). On an egress
failure, SMEP uses the BMLs in the stack to protect the egress
tunnel. The PLR node is required to install the MPLS forwarding
entries for the bypass tunnels using the BMLs. However, it does not
need to maintain a table that maps transport tunnels to backup paths.
Likewise, the PLR is not involved in the signaling of such
information. Instead, this information is supplied in the MPLS stack
from the ingress node to the PLR. Signaling is only needed between
ingress, egress, and the protector, but not with the PLR anymore.
Details of the signaling are not contained in this draft. The
general concepts and mechanisms described in [RFC8679] still apply.
3. Stack Management with POP-N-LSE Operation Network Action for SMEP
The MPLS Network Action (MNA) framework encodes network actions and
their data for processing by MPLS nodes. [I-D.ietf-mpls-mna-hdr]
defines the encoding of such network actions and their data in so-
called Network Action Substacks (NAS) in the MPLS stack.
[I-D.ihle-mpls-mna-stack-management-00] introduces a network action
for stack management. It features a POP-N-LSE operation that pops a
number POP-N of LSEs below the NAS. The POP-N-LSE operation
facilitates the application of SMEP. To that end, the POP-N-LSE
operation is added directly above the BMLs where POP-N is the number
of labels in the bypass tunnel. The processing at the PLR is as
follows:
1. If the PLR does not detect an egress failure
* The PLR executes the POP-N-LSE action and pops all BMLs.
* The packet is forwarded as usual to the egress node.
2. If the PLR detects an egress failure
* The POP-N-LSE action is ignored and is popped along with the
top-of-stack label.
* The BML is now the top-of-stack label. The packet is
forwarded to the protector based on the BML.
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4. Example
A simple example topology using MNA-based egress protection with an
SR bypass tunnel is shown in Figure 1. The example network contains
an LSP R1-R2-R3 and a bypass tunnel R2-R3'-R3''.
The MPLS stack using SMEP pushed by the ingress LER for the example
topology is shown in Figure 2. The label stack contains the
forwarding labels L1, L2, L3, L3', and L3'', and the POP-N-LSE
operation destined for the PLR. Since there are two BMLs to reach
the protector, POP-N = 2. Labels L1 and L2 are used to forward to
the penultimate router. Label L3 is used to route to the egress
node, and labels L3' and L3'' are used to route to the protector. If
the egress link or router R3 fails, the PLR can use the bypass tunnel
of router R3' and R3''.
/--L3'-- LSR ---L3''--- egress R3''
/ R3'
LSR
Ingress ───L1─── LSR ───L2─── R2 ───L3─── egress R3
LER R1 (PLR)
Figure 1: Example using the POP-N-LSE operation for SMEP.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-Label = L1 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-Label = L2 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-Label = L3 | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA-Label=bSPL (TBA) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opcode=MGMT |Reserved |POP-N=2| MOVE-N|R|IHS|S|U| NASL=0|NAL=0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-Label = L3' | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-Label = L3'' | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MPLS stack pushed by the ingress LER.
If there is no egress failure, the LSR R2 executes the POP-N-LSE
action with POP-N = 2 and pops the BMLs L3' and L3''. R2 pops the
top-of-stack label L3 and forwards the packet as usual to the egress.
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If the LSR R2 detects an egress failure, it becomes the PLR. The
POP-N-LSE action is ignored and the NAS is popped along with the top-
of-stack label. This stack is shown in Figure 1. This time, the
BMLs L3' and L3'' are at the top-of-stack. The packet is forwarded
according to those labels to the alternative egress node R3''.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-Label = L3' | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-Label = L3'' | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: MPLS stack at the PLR on egress failure.
5. Security Considerations
The security issues discussed in [I-D.ietf-mpls-mna-hdr] and in
[RFC8679] apply to this document.
6. IANA Considerations
This document makes no request of IANA.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
7.2. Informative References
[I-D.ietf-mpls-mna-hdr]
Rajamanickam, J., Gandhi, R., Zigler, R., Song, H., and K.
Kompella, "MPLS Network Action (MNA) Sub-Stack Solution",
Work in Progress, Internet-Draft, draft-ietf-mpls-mna-hdr-
12, 3 March 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-mpls-mna-hdr-12>.
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[I-D.ihle-mpls-mna-stack-management-00]
Ihle, F. and M. Menth, "MPLS Network Action for Stack
Management", Work in Progress, Internet-Draft, draft-ihle-
mpls-mna-stack-management-00, 13 June 2025,
<https://datatracker.ietf.org/doc/html/draft-ihle-mpls-
mna-stack-management-00>.
[RFC8679] Shen, Y., Jeganathan, M., Decraene, B., Gredler, H.,
Michel, C., and H. Chen, "MPLS Egress Protection
Framework", RFC 8679, DOI 10.17487/RFC8679, December 2019,
<https://www.rfc-editor.org/rfc/rfc8679>.
Authors' Addresses
Fabian Ihle
University of Tuebingen
Tuebingen
Germany
Email: fabian.ihle@uni-tuebingen.de
Michael Menth
University of Tuebingen
Tuebingen
Germany
Email: michael.menth@uni-tuebingen.de
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