LDP Extensions for Flex-Algo
draft-lin-mpls-ldp-flex-algo-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Changwang Lin , Yisong Liu | ||
| Last updated | 2025-04-15 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-lin-mpls-ldp-flex-algo-00
Network Working Group C. Lin
Internet Draft New H3C Technologies
Intended status: Standards Track Y. Liu
Expires: 20 October 2025 China Mobile
16 April 2025
LDP Extensions for Flex-Algo
draft-lin-mpls-ldp-flex-algo-00
Abstract
This document specifies extensions to LDP to support the use Flex-
Algo, enabling Label Switched Paths (LSPs) to follow a specific
Flex-Algo.
Status of this Memo
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This Internet-Draft will expire on 20 October 2025.
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Table of Contents
1. Introduction...................................................2
1.1. Terminology...............................................3
2. Signaling Extensions...........................................3
2.1. New Address Families: FA IP/FA IPv6.......................3
2.2. LDP FEC Elements with FA IP AF............................4
2.3. IGP IPA Mapping and Translation...........................5
2.4. LDP Flex-Algo Capability Advertisement....................5
2.4.1. Protocol Extension...................................5
2.4.2. Procedures...........................................6
3. FA Applicability on FEC-Based Features.........................7
3.1. Typed Wildcard FEC Element................................7
3.2. LSP Ping..................................................7
3.2.1. New FEC Sub-Types....................................7
3.2.2. FA LDP IPv4 FEC Sub-TLV..............................7
3.2.3. FA LDP IPv6 FEC Sub-TLV..............................8
3.2.4. Operation Considerations.............................8
4. Error Handling.................................................9
4.1. Error Notification for Invalid IPA ID.....................9
5. IANA Considerations............................................9
5.1. FA Capability TLV.........................................9
5.2. New Status Code...........................................9
5.3. New address families......................................9
6. References....................................................10
6.1. Normative References.....................................10
6.2. Informative References...................................10
Authors' Addresses...............................................10
1. Introduction
Multi-Topology Routing (MTR) is a technology that enables service
differentiation within an IP network. The Flexible Algorithm (FA) is
another mechanism for creating a sub-topology within a topology
using defined topology constraints and computation algorithms.
To deploy Label Distribution Protocol (LDP) in a network that
supports Flex-Algo, or other methods of signaling non-default IGP
Algorithms (IPAs), it is necessary for LDP to become algorithm
aware. This document specifies extensions to LDP to support the use
of IPAs, enabling Label Switched Paths (LSPs) to follow a specific
algorithm.
[RFC7307] describes how to extend the LDP protocol to support Multi-
Topology (MT), but it only uses one byte to carry the MT-ID and does
not support IPAs. This document updates RFC 7307 by allowing LSPs to
follow a specific topology and algorithm.
This document defines how LDP can utilize a specific combination of
topology and algorithm, referred to as Topology-Algorithm(TA). In
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this context, LDP's functionality is enhanced to ensure that the
LSPs are constructed and maintained according to the specified TA
parameters, thus optimizing the routing and resource utilization in
diverse network environments.
These enhancements to LDP provide the flexibility needed to support
advanced topological and algorithmic configurations, making it a
robust choice for modern, dynamic network infrastructures.
1.1. Terminology
This document uses terminologies defined in [RFC7307].
o MT-ID: A 16-bit value used to represent the Multi-Topology ID.
o Algorithm: A 1-octet value from the IGP Algorithm Types registry
under IGP Parameters registry.
2. Signaling Extensions
2.1. New Address Families: FA IP/FA IPv6
[RFC7307] defines MT IP and MT IPv6 address families, which are used
to specify IPv4 and IPv6 prefixes within a topology scope, but they
can only carry MT-ID information.
To extend IP address families for Flex-Algo, two new Address
Families named "FA IP" and "FA IPv6" are used to specify IPv4 and
IPv6 prefixes within a Flex-Algo scope.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: FA IP Address Family Format
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 Address |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: FA IPv6 Address Family Format
IPA: A 1-octet value from the IGP Algorithm Types registry under
IGP Parameters registry.
MT-ID: A 2-octet field MT-ID (see Section 3.7 of [RFC4915],
Section 7 of [RFC5120]) to special the topology. If this field is
set to zero, it means the default topology.
2.2. LDP FEC Elements with FA IP AF
The following section specifies the format extensions of the
existing LDP FEC elements to support Flex-Algo. The "Address
Family" of these FEC elements will be set to "FA IP" or "FA IPv6".
The encoding of the Flex-Algo Prefix FEC element is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix (2) | Address Family(FA IP/IPv6) | PreLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Prefix |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: FA Prefix FEC Element Format
The Flex-Algo Typed Wildcard FEC element encoding is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Typed Wcard (5)| FEC Type | Len = 6 | AF = FA IP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| or FA IPv6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Flex-Algo Typed Wildcard FEC Element
2.3. IGP IPA Mapping and Translation
The non-reserved non-special IGP IPA values can be used and carried
in LDP without the need for translation. However, there is a need
for translating reserved or special IGP IPA values to corresponding
LDP IPAs.
2.4. LDP Flex-Algo Capability Advertisement
2.4.1. Protocol Extension
We specify a new LDP capability, named "Flex-Algo (FA)", which is
defined in accordance with the LDP capability guidelines [RFC5561].
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The LDP "FA" capability can be advertised by an LDP speaker to its
peers either during the LDP session initialization or after the LDP
session is set up. The advertisement is to announce the capability
of the Label Switching Router (LSR) to support FA for the given IP
address family. An LDP speaker MUST NOT send messages containing FA
FEC elements unless the peer has said it can handle it.
The format of the FA Capability TLV is as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|U|F| Flex-Algo Cap.(IANA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved | |
+-+-+-+-+-+-+-+-+ |
~ Typed Wildcard FEC element(s) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Flex-Algo Capability TLV Format
Where:
o Flex-Algo Capability: Capability TLV type (IANA assigned)
2.4.2. Procedures
To announce its Flex-Algo capability for an IP address family, LDP
FEC type, an LDP speaker sends an "FA Capability" including the
exact Typed Wildcard FEC element with the corresponding
"AddressFamily" field (i.e., set to "FA IP" for IPv4 and set to "FA
IPv6" for IPv6 address family), corresponding "FEC Type" field
(i.e., set to "Prefix"), and corresponding "IPA". To announce its
Flex-Algo capability for both the IPv4 and IPv6 address family, or
for multiple FEC types, or for multiple Flex-Algos, an LDP speaker
sends an "FA Capability" with one or more FA Typed FEC elements in
it.
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3. FA Applicability on FEC-Based Features
3.1. Typed Wildcard FEC Element
[RFC5918] extends base LDP and defines the Typed Wildcard FEC
element framework. The Typed Wildcard FEC element can be used in
any LDP message to specify a wildcard operation/action for a given
type of FEC.
The FA extensions defined in this document do not require any
extension to procedures for the Typed Wildcard FEC element, and
these procedures apply as is to FA wildcarding. The FA extensions,
though, allow use of "FA IP" or "FA IPv6" in the Address Family
field of the Typed Wildcard FEC element in order to use wildcard
operations in the context of a given Flex-Algo. The use of FA-
scoped address family also allows us to specify Flex-Algo in these
operations.
3.2. LSP Ping
3.2.1. New FEC Sub-Types
We define two new FEC types for LSP ping:
o FA LDP IPv4 FEC
o FA LDP IPv6 FEC
3.2.2. FA LDP IPv4 FEC Sub-TLV
The format of the "FA LDP IPv4 FEC" sub-TLV to be used in a "Target
FEC Stack" [RFC4379] is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (FA LDP IPv4 FEC) | Length = 12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 5: FA LDP IPv4 FEC Sub-TLV
3.2.3. FA LDP IPv6 FEC Sub-TLV
The format of the "FA LDP IPv6 FEC" sub-TLV to be used in a "Target
FEC Stack" [RFC4379] is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (FA LDP IPv6 FEC) | Length = 24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: FA LDP IPv6 FEC Sub-TLV
3.2.4. Operation Considerations
To detect data-plane failures using LSP ping for a specific Flex-
Algo, the router will initiate an LSP ping request with the target
FEC stack TLV containing the LDP FA IP Prefix Sub-TLV in the Echo
Request packet. The Echo Request packet is sent with the label
bound to the IP Prefix in the Flex-Algo. Once the Echo Request
packet reaches the target router, it will process the packet and
perform checks for the LDP FA IP Prefix sub-TLV present in the
Target FEC Stack as described in [RFC4379] and respond according to
the processing rules in [RFC4379]. For the case that the LSP ping
with return path is not specified, the reply packet must go through
the default Flex-Algo instead of the Flex-Algo where the Echo
Request goes through.
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4. Error Handling
4.1. Error Notification for Invalid IPA ID
An LSR should respond with an "Invalid IPA ID" status code in the
LDP Notification message when it receives an LDP message with a FEC
element specifying an IPA that is not locally known or not
supported. The LSR MUST also discard the entire message before
sending the Notification message.
5. IANA Considerations
5.1. FA Capability TLV
New LDP Capability TLV "Flex-Algo Capability" TLV is requested
from the LDP Parameters registry "TLV Type Name Space".
5.2. New Status Code
A new status code, "Invalid IPA ID," was requested from the LDP
Parameters registry "Status Code Name Space".
Registry:
Range/Value Description
-------------- ------------------------------
TBD1 Invalid IPA ID
5.3. New address families
New address families under the IANA registry "Address Family
Numbers":
Number Description
-------- ------------------------------------
TBD2 FA IP: Flex-Algo IP version 4
TBD3 FA IPv6: Flex-Algo IP version 6
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6. References
6.1. Normative References
[RFC7307] Q. Zhao, Huawei Technology, K. Raza, C. Zhou, Cisco
Systems, L. Fang, Microsoft, L. Li, China Mobile, D. King,
Old Dog Consulting, "LDP Extensions for Multi-Topology",
RFC 5286,DOI 10.17487/RFC7307, July 2014,<http://www.rfc-
editor.org/info/rfc7307>.
[RFC9658] IJ. Wijnands, Individual, M. Mishra, Ed., K. Raza, Cisco
Systems, Inc., Z. Zhang, Juniper Networks, A. Gulko,
Edward Jones, "Multipoint LDP Extensions for Multi-
Topology Routing", RFC 9658,DOI 10.17487/RFC9658, October
2024,<http://www.rfc-editor.org/info/rfc9658>.
6.2. Informative References
TBD
Authors' Addresses
Changwang Lin
New H3C Technologies
China
Email: linchangwang.04414@h3c.com
Yisong Liu
China Mobile
China
Email: liuyisong@chinamobile.com
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