| Internet-Draft | Multi-Topology mLDP | June 2022 |
| Wijnands, et al. | Expires 31 December 2022 | [Page] |
- Workgroup:
- MPLS Working Group
- Internet-Draft:
- draft-ietf-mpls-mldp-multi-topology-00
- Published:
- Intended Status:
- Standards Track
- Expires:
mLDP Extensions for Multi-Topology Routing
Abstract
Multi-Topology Routing (MTR) is a technology to enable service differentiation within an IP network. Flexible Algorithm (FA) is another mechanism of creating a sub-topology within a topology using defined topology constraints and computation algorithm. In order to deploy mLDP in a network that supports MTR and/or FA, mLDP is required to become topology and FA aware. This document specifies extensions to mLDP to support MTR with FA such that when building a Multi-Point LSPs it can follow a particular topology and algorithm.¶
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 31 December 2022.¶
Copyright Notice
Copyright (c) 2022 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
1. Glossary
- MT - Multi-Topology¶
- MT-ID - Multi-Topology Identifier¶
- MTR - Multi-Topology Routing¶
- IGP - Interior Gateway Protocol¶
- MP - Multipoint (P2MP or MP2MP)¶
- LDP - Label Distribution Protocol¶
- mLDP - Multipoint LDP¶
- P2MP - Point-to-Multipoint¶
- MP2MP - Multipoint-to-Multipoint¶
- FEC - Forwarding Equivalence Class¶
- LSP - Label Switched Path¶
- FA - Flexible Algorithm¶
- IPA - IGP Algorithm¶
2. Introduction
Multi-Topology Routing (MTR) is a technology to enable service differentiation within an IP network. IGP protocols (OSPF and IS-IS) and LDP have already been extended to support MTR. To support MTR, an IGP maintains independent IP topologies, termed as "Multi-Topologies" (MT), and computes/installs routes per topology. OSPF extensions [RFC4915] and ISIS extensions [RFC5120] specify the MT extensions under respective IGPs. To support IGP MT, similar LDP extensions [RFC7307] have been specified to make LDP MT-aware and be able to setup unicast Label Switched Paths (LSPs) along IGP MT routing paths.¶
A more light weight mechanism to define constraint-based topologies is Flexible Algorithm (FA) [I-D.ietf-lsr-flex-algo]. FA can be seen as creating a sub-topology within a topology using defined topology constraints and computation algorithm. This can be done within a MTR topology or just the default Topology. An instance of such a sub-topology is identified by a 1 octet value as documented in [I-D.ietf-lsr-flex-algo]). Flexible Algorithm is a mechanism to create a sub-topology, but in the future different algorithms might be defined on how to achieve that. For that reason, in the remainder of this document we'll refer to this as the IGP Algorithm (IPA).¶
Multipoint LDP (mLDP) refers to extensions in LDP to setup multi-point LSPs (point-to-multipoint (P2MP) or multipoint-to-multipoint (MP2MP)), by means of set of extensions and procedures defined in [RFC6388]. In order to deploy mLDP in a network that supports MTR and FA, mLDP is required to become topology and algorithm aware. This document specifies extensions to mLDP to support MTR/IPA such that when building a Multi-Point LSPs it can follow a particular topology and alogirthm. This means that the identifier for the particular Topology to be used by mLDP have to become a two tuple (MTR Topology Id, IGP Algorithm).¶
3. Specification of Requirements
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].¶
In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying RFC-2119 significance.¶
4. MT Scoped mLDP FECs
As defined in [RFC7307], MPLS Multi-Topology Identifier (MT-ID) is an identifier that is used to associate an LSP with a certain MTR topology. In the context of MP LSPs, this identifier is part of the mLDP FEC encoding so that LDP peers are able to setup an MP LSP via their own defined MTR policy. In order to avoid conflicting MTR policies for the same mLDP FEC, the MT-ID needs to be a part of the FEC, so that different MT-ID values will result in unique MP-LSP FEC elements.¶
The same applies to the IPA. The IPA needs to be encoded as part of the mLDP FEC to create unique MP-LSPs and at the same time is used to signal to mLDP (hop-by-hop) which Algorithm needs to be used to create the MP-LSP.¶
Since the MT-ID and IPA are part of the FEC, they apply to all the LDP messages that potentially include an mLDP FEC element.¶
4.1. MP FEC Extensions for MT
Following subsections propose the extensions to bind an mLDP FEC to a topology. The mLDP MT extensions reuse some of the extensions specified in [RFC7307].¶
4.1.1. MP FEC Element
Base mLDP specification [RFC6388] defines MP FEC Element 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MP FEC type | Address Family | AF Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Root Node Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Length | Opaque Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where "Root Node Address" encoding is as defined for given "Address Family", and whose length (in octets) is specified by the "AF Length" field.¶
To extend MP FEC elements for MT, the {MT-ID, IPA} is a tuple that is relevant in the context of the root address of the MP LSP. The {MT-ID, IPA} tuple determines in which (sub)-topology the root address needs to be resolved. Since the {MT-ID, IPA} tuple should be considered part of the mLDP FEC, the most natural place to encode this tuple is as part of the root address. While encoding it, we also propose to use "MT IP" Address Families as described in following sub section.¶
4.1.2. MT IP Address Families
[RFC7307] has specified new address families, named "MT IP" and "MT IPv6", to allow specification of an IP prefix within a topology scope. In addition to using this address family for mLDP, we also use 8 bits of the 16 bits Reserved field to encode the IGP Algorithm (IPA) Registry. The resulting format of the data associated with these new Address Families 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:¶
4.1.3. MT MP FEC Element
By using extended MT IP Address Family, the resultant MT MP FEC element is to be encoded 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MP FEC type | AF (MT IP/ MT IPv6) | AF Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Root Node Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Length | Opaque Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
In the context of this document, the applicable LDP FECs for MT mLDP include:¶
In case of "Typed Wildcard FEC Element", the sub FEC Element type MUST be one of the MP FECs listed above.¶
This specification allows the use of Topology-scoped mLDP FECs in LDP label and notification messages, as applicable.¶
4.2. Topology IDs
This document assumes the same definitions and procedures associated with MPLS MT-ID as defined in [RFC7307] specification.¶
5. MT Multipoint Capability
"MT Multipoint Capability" is a new LDP capability, defined in accordance with LDP Capability definition guidelines [RFC5561], that is to be advertised to its peers by an mLDP speaker to announce its capability to support MTR and the procedures specified in this document. This capability MAY be sent either in an Initialization message at the session establishment time, or in a Capability message dynamically during the lifetime of a session (only if "Dynamic Announcement" capability [RFC5561] has been successfully negotiated with the peer).¶
The format of this capability 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| MT Multipoint Cap.(IANA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+
Where:¶
- U- and F-bits: MUST be 1 and 0, respectively, as per Section 3 of LDP Capabilities [RFC5561].¶
- MT Multipoint Capaility: TLV type (IANA assigned).¶
- Length: The length (in octets) of TLV. The value of this field MUST be 1 as there is no Capability-specific data [RFC5561] that follows in the TLV.¶
- S-bit: Set to 1 to announce and 0 to withdraw the capability (as per [RFC5561].¶
An mLDP speaker that has successfully advertised and negotiated "MT Multipoint" capability MUST support the following:¶
- Topology-scoped mLDP FECs in LDP messages (Section 4.1)¶
- Topology-scoped mLDP forwarding setup (Section 7)¶
6. MT Applicability on FEC-based features
6.1. Typed Wildcard MP FEC Elements
[RFC5918] extends base LDP and defines Typed Wildcard FEC Element framework. Typed Wildcard FEC element can be used in any LDP message to specify a wildcard operation for a given type of FEC.¶
The MT extensions proposed in document do not require any extension in procedures for Typed Wildcard FEC Element support [RFC5918], and these procedures apply as-is to Multipoint MT FEC wildcarding. Like Typed Wildcard MT Prefix FEC Element, as defined in [RFC7307], the MT extensions allow use of "MT IP" or "MT IPv6" in the Address Family field of the Typed Wildcard MP FEC element in order to use wildcard operations for MP FECs in the context of a given (sub)-topology as identified by the MT-ID and IPA field.¶
This document proposes following format and encoding for a Typed Wildcard MP FEC element:¶
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)| Type = MP FEC | Len = 6 | AF = MT IP ..|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|... or MT IPv6 | Reserved | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MT ID (contd.) |
+-+-+-+-+-+-+-+-+
Where:¶
- Type: One of MP FEC Element type (P2MP, MP2MPup, MP2MP-down).¶
- MT ID: MPLS MT ID¶
- IPA: The IGP Algorithm, values are from the IGP Algorithm registry.¶
The proposed format allows an LSR to perform wildcard MP FEC operations under the scope of a (sub-)topology.¶
6.2. End-of-LIB
[RFC5919] specifies extensions and procedures that allows an LDP speaker to signal its End-of-LIB (i.e. convergence) for a given FEC type towards a peer. MT extensions for MP FEC do not require any change in these procedures and they apply as-is to MT MP FEC elements. This means that an MT mLDP speaker MAY signal its convergence per (sub-)topology using MT Typed Wildcard MP FEC element.¶
7. Topology-Scoped Signaling and Forwarding
Since the {MT-ID, IPA} tuple is part of an mLDP FEC, there is no need to support the concept of multiple (sub-)topology forwarding tables in mLDP. Each MP LSP will be unique due to the tuple being part of the FEC. There is also no need to have specific label forwarding tables per topology, and each MP LSP will have its own unique local label in the table. However, In order to implement MTR in an mLDP network, the selection procedures for upstream LSR and downstream forwarding interface need to be changed.¶
7.1. Upstream LSR selection
The procedures as described in RFC-6388 section-2.4.1.1 depend on the best path to reach the root. When the {MT-ID, IPA} tuple is signaled as part of the FEC, this tuple is used to select the (sub-)topology that must be used to find the best path to the root address. Using the next-hop from this best path, a LDP peer is selected following the procedures as defined in [RFC6388].¶
7.2. Downstream forwarding interface selection
The procedures as described in RFC-6388 section-2.4.1.2 describe how a downstream forwarding interface is selected. In these procedures, any interface leading to the downstream LDP neighbor can be considered as candidate forwarding interface. When the {MT-ID, IPA} tuple is part of the FEC, this is no longer true. An interface must only be selected if it is part of the same (sub-)topology that was signaled in the mLDP FEC element. Besides this restriction, the other procedures in [RFC6388] apply.¶
8. LSP Ping Extensions
[RFC6425] defines procedures to detect data plane failures in Multipoint MPLS LSPs. Section 3.1.2 of [RFC6425] defines new Sub- Types and Sub-TLVs for Multipoint LDP FECs to be sent in "Target FEC Stack" TLV of an MPLS echo request message [RFC4379].¶
To support LSP ping for MT Multipoint LSPs, this document uses existing sub-types "P2MP LDP FEC Stack" and "MP2MP LDP FEC Stack" defined in [RFC6425]. The proposed extension is to specify "MT IP" or "MT IPv6" in the "Address Family" field, set the "Address Length" field to 8 (for MT IP) or 20 (for MT IPv6), and encode the sub-TLV with additional {MT-ID, IPA} information as an extension to the "Root LSR Address" field. The resultant format of sub-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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Address Family (MT IP/MT IPv6) | Address Length| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ Root LSR Address (Cont.) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | IPA | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Length | Opaque Value ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The rules and procedures of using this new sub-TLV in an MPLS echo request message are same as defined for P2MP/MP2MP LDP FEC Stack Sub-TLV in [RFC6425] with only difference being that Root LSR address is now (sub-)topology scoped.¶
9. Security Considerations
This extension to mLDP does not introduce any new security considerations beyond that already apply to the base LDP specification [RFC5036], base mLDP specification [RFC6388], and MPLS security framework [RFC5920].¶
10. IANA Considerations
This document defines a new LDP capability parameter TLV. IANA is requested to assign the lowest available value after 0x0500 from "TLV Type Name Space" in the "Label Distribution Protocol (LDP) Parameters" registry within "Label Distribution Protocol (LDP) Name Spaces" as the new code point for the LDP TLV code point.¶
+-----+------------------+---------------+-------------------------+ |Value| Description | Reference | Notes/Registration Date | +-----+------------------+---------------+-------------------------+ | TBA | MT Multipoint | This document | | | | Capability | | | +-----+------------------+---------------+-------------------------+
11. Acknowledgments
The authors would like to acknowledge Eric Rosen for his input on this specification.¶
12. References
12.1. Normative References
- [I-D.ietf-lsr-flex-algo]
- Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and A. Gulko, "IGP Flexible Algorithm", Work in Progress, Internet-Draft, draft-ietf-lsr-flex-algo-20, , <https://www.ietf.org/archive/id/draft-ietf-lsr-flex-algo-20.txt>.
- [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>.
- [RFC4379]
- Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures", RFC 4379, DOI 10.17487/RFC4379, , <https://www.rfc-editor.org/info/rfc4379>.
- [RFC4915]
- Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, DOI 10.17487/RFC4915, , <https://www.rfc-editor.org/info/rfc4915>.
- [RFC5120]
- Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, , <https://www.rfc-editor.org/info/rfc5120>.
- [RFC6388]
- Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B. Thomas, "Label Distribution Protocol Extensions for Point-to-Multipoint and Multipoint-to-Multipoint Label Switched Paths", RFC 6388, DOI 10.17487/RFC6388, , <https://www.rfc-editor.org/info/rfc6388>.
- [RFC6425]
- Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A., Yasukawa, S., and T. Nadeau, "Detecting Data-Plane Failures in Point-to-Multipoint MPLS - Extensions to LSP Ping", RFC 6425, DOI 10.17487/RFC6425, , <https://www.rfc-editor.org/info/rfc6425>.
- [RFC7307]
- Zhao, Q., Raza, K., Zhou, C., Fang, L., Li, L., and D. King, "LDP Extensions for Multi-Topology", RFC 7307, DOI 10.17487/RFC7307, , <https://www.rfc-editor.org/info/rfc7307>.
12.2. Informative References
- [RFC5036]
- Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed., "LDP Specification", RFC 5036, DOI 10.17487/RFC5036, , <https://www.rfc-editor.org/info/rfc5036>.
- [RFC5561]
- Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL. Le Roux, "LDP Capabilities", RFC 5561, DOI 10.17487/RFC5561, , <https://www.rfc-editor.org/info/rfc5561>.
- [RFC5918]
- Asati, R., Minei, I., and B. Thomas, "Label Distribution Protocol (LDP) 'Typed Wildcard' Forward Equivalence Class (FEC)", RFC 5918, DOI 10.17487/RFC5918, , <https://www.rfc-editor.org/info/rfc5918>.
- [RFC5919]
- Asati, R., Mohapatra, P., Chen, E., and B. Thomas, "Signaling LDP Label Advertisement Completion", RFC 5919, DOI 10.17487/RFC5919, , <https://www.rfc-editor.org/info/rfc5919>.
- [RFC5920]
- Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", RFC 5920, DOI 10.17487/RFC5920, , <https://www.rfc-editor.org/info/rfc5920>.
