RFC 7307
LDP Extensions for Multi-Topology
RFC 7307: LDP Extensions for Multi-Topology ✨
Okay bestie, this is RFC 7307 🎀 It's a Standards Track document, which means it's an actual Internet standard and not just a suggestion 💅 It was published in July 2014 under ISSN 2070-1721. The authors are Q. Zhao (Huawei Technology), K. Raza and C. Zhou (both Cisco Systems), L. Fang (Microsoft), L. Li (China Mobile), and D. King (Old Dog Consulting) 🫶 The title block doesn't list anything this one obsoletes or updates, so it's standing on its own 🦋
Abstract
Multi-Topology (MT) routing already works in IP networks thanks to MT-aware IGPs 🌸 To bring MT routing into MPLS networks that run the Label Distribution Protocol (LDP), new extensions are required 💖
This document explains the LDP protocol extensions needed to make MT routing work in an MPLS environment ✨
Status of This Memo
This is an Internet Standards Track document 🎀
This document is a product of the Internet Engineering Task Force (IETF) 🌈 It reflects what the IETF community agrees on. It went through public review and the Internet Engineering Steering Group (IESG) approved it for publication 💅 If you want more info on Internet Standards, check Section 2 of RFC 5741 📚
For the latest status, any errata, and how to send feedback, go to http://www.rfc-editor.org/info/rfc7307 🦋
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved 💜
This document is covered by BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stood on the publication date 🌸 Read these carefully, because they spell out your rights and restrictions for this document 👑 Any Code Components pulled out of this document must include the Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions. They come with no warranty, as the Simplified BSD License describes 🫶
Table of Contents
1. Introduction ....................................................4
2. Terminology .....................................................4
3. Signaling Extensions ............................................5
3.1. Topology-Scoped Forwarding Equivalence Class (FEC) .........5
3.2. New Address Families: MT IP ................................5
3.3. LDP FEC Elements with MT IP AF .............................6
3.4. IGP MT-ID Mapping and Translation ..........................7
3.5. LDP MT Capability Advertisement ............................7
3.5.1. Protocol Extension ..................................7
3.5.2. Procedures ..........................................9
3.6. Label Spaces ..............................................10
3.7. Reserved MT-ID Values .....................................10
4. MT Applicability on FEC-Based Features .........................10
4.1. Typed Wildcard FEC Element ................................10
4.2. Signaling LDP Label Advertisement Completion ..............11
4.3. LSP Ping ..................................................11
4.3.1. New FEC Sub-Types ..................................11
4.3.2. MT LDP IPv4 FEC Sub-TLV ............................12
4.3.3. MT LDP IPv6 FEC Sub-TLV ............................13
4.3.4. Operation Considerations ...........................13
5. Error Handling .................................................14
5.1. MT Error Notification for Invalid Topology ID .............14
6. Backwards Compatibility ........................................14
7. MPLS Forwarding in MT ..........................................14
8. Security Considerations ........................................14
9. IANA Considerations ............................................15
10. Manageability Considerations ..................................17
10.1. Control of Function and Policy ...........................17
10.2. Information and Data Models ..............................17
10.3. Liveness Detection and Monitoring ........................17
10.4. Verify Correct Operations ................................17
10.5. Requirements on Other Protocols ..........................17
10.6. Impact on Network Operations .............................17
11. Contributors ..................................................18
12. Acknowledgements ..............................................19
13. References ....................................................19
13.1. Normative References .....................................19
13.2. Informative References ...................................191. Introduction ✨
Multi-Topology (MT) routing is supported in IP networks using MT-aware IGPs 🌸 It would be really useful for Communications Service Providers (CSPs) to run an MPLS Multi-Topology (MPLS-MT) environment 💅 MPLS-MT brings features for a bunch of different network scenarios, including:
- A CSP might want to give different traffic classes different Quality of Service (QoS) profiles, based on a specific topology in an MT routing network 💖
- Separate routing and MPLS domains might be used to isolate multicast and IPv6 islands inside the backbone network 🧚
- Specific IP address space could be routed across an MT based on security or operational isolation requirements 🔒
- Low-latency links could be assigned to an MT for delay-sensitive traffic ⚡
- Management traffic may be separated from customer traffic by using different MTs over separate links, which makes sure management traffic stays apart from customer traffic 🫶
This document describes the Label Distribution Protocol (LDP) procedures and protocol extensions needed to support MT routing in an MPLS environment 🦋
This document defines two new Forwarding Equivalence Class (FEC) types for use in Label Switched Path (LSP) ping [RFC4379] 🎀
2. Terminology
This document uses MPLS terminology defined in [RFC5036]. There are a few more terms defined below 📚
- MT-ID: A 16-bit value used to represent the Multi-Topology ID.
- Default MT Topology: A topology that is built using the MT-ID default value of 0.
- MT Topology: A topology that is built using the corresponding MT-ID.
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 RFC 2119 [RFC2119] 👑
3. Signaling Extensions
3.1. Topology-Scoped Forwarding Equivalence Class (FEC)
LDP assigns and binds a label to a FEC, and a FEC is a list of one or more FEC elements 💅 To set up LSPs for unicast IP routing paths, LDP assigns local labels for IP prefixes and advertises those labels to its peers, so an LSP gets built along the routing path 🌈 To set up MT LSPs for IP prefixes under a given topology scope, the LDP prefix-related FEC element must be extended to include topology information. That means the MT-ID becomes an attribute of the prefix-related FEC element, and every FEC-Label binding operation runs in the context of a given topology (MT-ID) 🧚
The next section ("New Address Families: MT IP") defines the extension needed to bind the prefix-related FEC to a topology 🦋
3.2. New Address Families: MT IP
Section 2.1 of the LDP base specification [RFC5036] defines the Address Prefix FEC element 📚 The Prefix encoding is defined for a given "Address Family" (AF), and its length (in bits) is set by the "PreLen" field ✨
To extend the IP address families for MT, two new Address Families, "MT IP" and "MT IPv6", are used to specify IPv4 and IPv6 prefixes within a topology scope 💖 The format of the data for these new Address Families looks like this:
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 | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: MT IP Address Family Format
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 | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MT IPv6 Address Family FormatHere, "IP Address" is the IPv4 or IPv6 address/prefix for the "MT IP" and "MT IPv6" AF respectively, and the "MT-ID" field holds the 16-bit Topology ID for that address 🎀
The definition and usage of the remaining fields in the FEC elements are the same as for the IP/IPv6 AF. The MT-ID value 0 maps to the default topology and MUST be ignored on receipt, so it doesn't cause any conflict or confusion with existing non-MT procedures 🙈
The FEC elements with the "MT IP" Address Family can be used in any LDP message and procedure that already specifies and allows FEC elements with the IP/IPv6 Address Family 🌸
3.3. LDP FEC Elements with MT IP AF 🎀
okay so this bit is where we tweak the existing LDP FEC elements so they can handle MT ✨ The "Address Family" on these FEC elements gets set to MT IP or MT IPv6. Here's the MT Prefix FEC element, slay 💅
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 (MT IP/MT IPv6)| PreLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: MT Prefix FEC Element FormatAnd here's the MT Typed Wildcard FEC element, which is giving layers 🧚
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 = MT IP ..|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|... or MT IPv6 | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: MT Typed Wildcard FEC ElementThe above format can be used for any LDP FEC element that allows use of the IP/IPv6 Address Family. In the scope of this document, the allowed "FEC Type" in a MT Typed Wildcard FEC element is the Prefix FEC element. Only Prefix, bestie 🌸
3.4. IGP MT-ID Mapping and Translation 🦋
ngl this one is about MT-ID values. The non-reserved, non-special IGP MT-ID values can be used and carried in LDP without any translation, which is so convenient 🙌 But reserved or special IGP MT-IDs DO need translating to the matching LDP MT-IDs. The assigned, unassigned, and special LDP MT-ID values are laid out in Section 9 ("IANA Considerations") 📋
How future LDP MT-ID values get allocated is out of scope for this doc. Instead, a separate document is going to be made to detail the allocation policy and the process for requesting new MT-ID values. Stay tuned, it's a whole other plot 🍓
3.5. LDP MT Capability Advertisement 📢
3.5.1. Protocol Extension
We're specifying a new LDP capability called "Multi-Topology (MT)", defined under the LDP capability guidelines in [RFC5561]. An LDP speaker can advertise the "MT" capability to its peers either during LDP session initialization or after the session is already set up. The whole point is to announce that the Label Switching Router (LSR) can support MT for a given IP address family. Big rule here: an LDP speaker MUST NOT send messages containing MT FEC elements unless the peer has said it can handle it. Respect the consent, periodt 🙅♀️
The MT capability is specified using the Multi-Topology Capability TLV, and that TLV follows the LDP capability guidelines from [RFC5561]. To specify the IP address family, the capability-specific data (the "Capability Data" field of the Capability TLV) gets filled in using the "Typed Wildcard FEC element" from [RFC5918]. The format of the Multi-Topology Capability TLV looks like this 👇
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| Multi-Topology Cap.(IANA) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S| Reserved | |
+-+-+-+-+-+-+-+-+ |
~ Typed Wildcard FEC element(s) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Multi-Topology Capability TLV FormatWhere the fields go:
- U-bit: MUST be 1 so that the TLV will be silently ignored by a recipient if it is unknown, according to the rules of [RFC5036].
- F-bit: MUST be 0 as per Section 3 ("Specifying Capabilities in LDP Messages") of LDP Capabilities [RFC5561].
- Multi-Topology Capability: Capability TLV type (IANA assigned).
- S-bit: MUST be 1 if used in LDP "Initialization" message. MAY be set to 0 or 1 in dynamic "Capability" message to advertise or withdraw the capability, respectively.
- Typed Wildcard FEC element(s): One or more elements specified as the "Capability data".
- Length: length of Value field, starting from the S-bit, in octets.
- The encoding of the Typed Wildcard FEC element, as defined in [RFC5918], is defined in Section 4.1 ("Typed Wildcard FEC element") of this document. The MT-ID field of the MT Typed Wildcard FEC element MUST be set to "Wildcard Topology" when it is specified in the MT Capability TLV.
3.5.2. Procedures
To announce its MT capability for an IP address family, LDP FEC type, and Multi-Topology, an LDP speaker sends an "MT Capability" including the exact Typed Wildcard FEC element with the corresponding "AddressFamily" field (so MT IP for IPv4 and MT IPv6 for IPv6), the corresponding "FEC Type" field (set to "Prefix"), and the corresponding "MT-ID". Want MT for both IPv4 and IPv6, or for multiple FEC types, or for multiple Multi-Topologies? Then the speaker sends an "MT Capability" with one or more MT Typed FEC elements in it. Easy 💖
- The capability for supporting multi-topology in LDP can be advertised during the LDP session initialization stage by including the LDP MT capability TLV in the LDP Initialization message. After an LDP session is established, the MT capability can also be advertised or withdrawn using the Capability message (only if the "Dynamic Capability Announcement" capability [RFC5561] has already been successfully negotiated).
- If an LSR has not advertised MT capability, its peer MUST NOT send to this LSR any LDP messages with FEC elements that include an MT identifier.
- If an LSR is changed from non-MT capable to MT capable, it sets the S-bit in the MT capability TLV and advertises via the Capability message (if it supports Dynamic Capability Announcement). The existing LSP is treated as an LSP for default MT (ID 0). 🌈
- If an LSR is changed from LDP-MT capable to non-MT capable, it initiates withdrawal of all label mapping for existing LSPs of all non-default MTs. It also cleans up all the LSPs of all non-default MTs locally. Then, it clears the S-bit in the MT capability TLV and advertises via the Capability message (if it supports Dynamic Capability Announcement). When an LSR knows the peer node is changed from LDP-MT capable to non-MT capable, it cleans up all the LSPs of all non-default MTs locally and initiates withdrawal of all label mapping for existing LSPs of all non-default MTs. Each side of the node sends a label release to its peer once it receives the label release messages, even though each side has already cleaned up all the LSPs locally. It's a whole group project 😭
- If an LSR does not support "Dynamic Capability Announcement", it MUST reset the session with its peer whenever the LSR changes its local capability with regards to supporting LDP MT.
- If an LSR is changed from IGP-MT capable to non-MT capable, it may wait until the routes update to withdraw the FEC and release the label mapping for existing LSPs of a specific MT.
3.6. Label Spaces 🫧
Using multiple topologies for LDP does NOT need separate label spaces for each topology. An LSR can use the same label space for all MT FECs as it does for the default topology. Same vibes, same space ✨
Similarly, signaling for different topologies can and should be done within a single LDP session. One session, many topologies, zero drama 🫶
3.7. Reserved MT-ID Values 👑
Certain MT topologies are assigned to serve predetermined purposes, so they're kind of VIP 💅
In Section 9 ("IANA Considerations"), this document defines a new IANA registry called "MPLS Multi-Topology Identifiers" to keep the LDP MT-ID reserved values.
If an LSR receives a FEC element with an "MT-ID" value that is "Unassigned" for future use (and not IANA allocated yet), the LSR MUST abort the processing of the FEC element and SHOULD send a notification message with status code "Invalid Topology ID" to the sender. > bestie, don't process an unassigned MT-ID, it's not ready yet 🙈
4. MT Applicability on FEC-Based Features ✨
4.1. 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 or action for a given type of FEC.
The MT extensions in this document don't need any extra procedures for the Typed Wildcard FEC element, so the existing procedures apply as is to MT wildcarding. The MT extensions do let you use MT IP or MT IPv6 in the Address Family field of the Typed Wildcard FEC element, so wildcard operations can be scoped to a given topology. Using an MT-scoped address family also lets you specify an MT-ID in these operations 🦋
The format defined in Section 4.1 ("Typed Wildcard FEC element") lets an LSR perform wildcard FEC operations under the scope of a topology. If an LSR wants a wildcard operation that covers ALL topologies, it can use the "Wildcard Topology" MT-ID.
For example, when a topology "x" gets locally de-configured, an LSR may send a typed wildcard Label Withdraw message with MT-ID "x" to withdraw all its labels from the peer that advertised under the scope of topology "x". And if there's a global configuration change, an LSR may send a typed wildcard Label Withdraw message with the MT-ID set to "Wildcard Topology" to withdraw all its labels under all topologies from the peer. Clean slate, big energy 🧹
4.2. Signaling LDP Label Advertisement Completion 📣
[RFC5919] specifies extensions and procedures for an LDP speaker to signal its convergence for a given FEC type towards a peer. The procedures defined in [RFC5919] apply as they are to an MT FEC element. This means an LDP speaker can signal its IP convergence using the Typed Wildcard FEC element, and its MT IP convergence per topology using an MT Typed Wildcard FEC element. Convergence, but make it topological 🌸
4.3. LSP Ping 🏓
[RFC4379] defines procedures to detect data-plane failures in MPLS LSPs via LSP ping. That specification defines a "Target FEC Stack" TLV that describes the FEC stack being tested. This TLV is sent in an MPLS Echo Request message towards the LSP's egress LSR and is forwarded along the same data path as other packets belonging to the FEC.
"Target FEC Stack" TLV contains one or more sub-TLVs pertaining to different FEC types. Section 3.2 of [RFC4379] defines the Sub-Types and format of the FEC. To support LSP ping for MT LDP LSPs, this document defines the following extensions to [RFC4379].
4.3.1. New FEC Sub-Types ✨
okay so we're adding two brand-new FEC types for LSP ping 💅
- MT LDP IPv4 FEC
- MT LDP IPv6 FEC
we also define new sub-types for sub-TLVs so these FECs can be specified in the "Target FEC Stack" TLV of [RFC4379] 🦋
Sub-Type Length Value Field
-------- ------ -----------------
31 8 MT LDP IPv4 prefix
32 20 MT LDP IPv6 prefixFigure 6: New Sub-Types for Sub-TLVs
the rules and procedures for using these sub-TLVs in an MPLS echo request message are the same as the ones for the LDP IPv4/IPv6 FEC sub-TLV types in [RFC4379]. no new rulebook, bestie 🫶
4.3.2. MT LDP IPv4 FEC Sub-TLV 🌸
the format of the "MT LDP IPv4 FEC" sub-TLV, used in a "Target FEC Stack" [RFC4379], looks like this:
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 = 31 (MT LDP IPv4 FEC) | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | MBZ | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Figure 7: MT LDP IPv4 FEC Sub-TLV
this sub-TLV is basically a glow-up of the LDP IPv4 FEC sub-TLV from [RFC4379] ✨ it keeps the "IPv4 prefix" and "Prefix Length" fields, and then adds the MT-ID (Multi-Topology ID) on top. the Length for this sub-TLV is 5.
quick vocab check 🧠 the term "Must Be Zero" (MBZ) shows up in object descriptions for reserved fields. These fields MUST be set to zero when sent and ignored on receipt. no exceptions, periodt 💀
4.3.3. MT LDP IPv6 FEC Sub-TLV 💜
the format of the "MT LDP IPv6 FEC" sub-TLV, 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 = 32 (MT LDP IPv6 FEC) | Length = 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 prefix |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | MBZ | MT-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Figure 8: MT LDP IPv6 FEC Sub-TLV
same energy as the IPv4 one 🫶 it's similar to the LDP IPv6 FEC sub-TLV in [RFC4379], with the "IPv6 prefix" and "Prefix Length" fields plus the MT-ID (Multi-Topology ID). the Length for this sub-TLV is 17.
4.3.4. Operation Considerations 🧚
okay, here's how you actually detect data-plane failures with LSP ping for one specific topology 👀 the router starts an LSP ping request with the target FEC stack TLV containing the LDP MT IP Prefix Sub-TLV, sent in the Echo Request packet. the Echo Request goes out with the label bound to the IP Prefix in that topology. once it reaches the target router, the router processes the packet, checks for the LDP MT IP Prefix sub-TLV in the Target FEC Stack (as described in [RFC4379]), and responds using the processing rules in [RFC4379]. if the LSP ping has no return path specified, the reply packet must go through the default topology instead of the topology the Echo Request traveled through. the plot twist 🙈
it should be noted that the existing MIB modules for an MPLS LSR [RFC3813] and MPLS LDP managed objects [RFC3815] don't give you the info needed to support these extensions 😭 for example, since the MT-ID isn't an index into those MIB modules, there's no way to tell different topology instances apart. rip to the MIBs.
5. Error Handling ✨
the extensions in this document use the LDP error handling that already exists in [RFC5036] 💅 if an LSR gets an error notification from a peer for a session, it tears the LDP session down by closing the TCP transport connection for that session, and it throws away all the multi-topology label mappings it learned through that session. dramatic exit, iconic 🔥
5.1. MT Error Notification for Invalid Topology ID 🚨
an LSR should respond with an "Invalid Topology ID" status code in the LDP Notification message when it gets an LDP message with a FEC element that specifies an MT-ID which is not locally known or not supported. The LSR MUST also discard the entire message before sending the Notification message. so it ditches the whole message first, then sends the notification 🫶
6. Backwards Compatibility 🦋
the MPLS-MT solution is backwards compatible with existing LDP enhancements defined in [RFC5036], including message authenticity, integrity of message, and topology loop detection. it plays nice with the old stuff 🌈
a legacy node that doesn't support MT should not receive any MT-related LDP messages. in case bad things happen, processing of such messages should be aborted according to [RFC5036] 💀
7. MPLS Forwarding in MT 🌸
forwarding is technically out of scope for this document, but we're including some forwarding considerations here for informational purposes, because we love context 🧚
the signaling mechanisms allow all the topologies to share the platform-specific label space, so the existing data-plane techniques can be used. there's also no way for the data plane to associate a received packet with any one topology, which means topology-specific label spaces can't be used. so it's all one shared label space, no separate lanes 🛣️
8. Security Considerations 🔐
the use of MT over existing MPLS solutions does not offer any specific security benefit. so don't expect a security glow-up from this part 😭
general LDP communication security threats, and how they can be mitigated, are described in [RFC5036]. these threats include:
- spoofing
- privacy
- denial of service
for more on possible LDP communication threats and mitigation techniques, check out [RFC5920] 🧠 please read this part seriously, bestie 💖
9. IANA Considerations 📋
this document introduces the following new protocol elements, which IANA has assigned:
- New LDP Capability TLV: "Multi-Topology Capability" TLV (0x050C) from the LDP Parameters registry "TLV Type Name Space".
- New Status Code: "Invalid Topology ID" (0x00000031) from the LDP Parameters registry "Status Code Name Space").
Registry:
Range/Value Description
-------------- ------------------------------
0x00000031 Invalid Topology IDFigure 9: New Code Point for LDP Multi-Topology Extensions
- New address families under the IANA registry "Address Family Numbers":
Number Description
-------- ------------------------------------
29 MT IP: Multi-Topology IP version 4
30 MT IPv6: Multi-Topology IP version 6Figure 10: Address Family Numbers
- New registry "MPLS Multi-Topology Identifiers". This is a registry of the "Multiprotocol Label Switching Architecture (MPLS)" category. The initial registrations and allocation policies for this registry are:
Range/Value Purpose Reference
----------- ------------------------------------- ----------
0 Default/standard topology RFC 7307
1 IPv4 in-band management RFC 7307
2 IPv6 routing topology RFC 7307
3 IPv4 multicast topology RFC 7307
4 IPv6 multicast topology RFC 7307
5 IPv6 in-band management RFC 7307
6-3995 Unassigned for future IGP topologies RFC 7307
Assigned by Standards Action RFC 7307
3996-4095 Experimental RFC 7307
4096-65534 Unassigned for MPLS topologies RFC 7307
Assigned by Standards Action
65535 Wildcard Topology RFC 7307Figure 11: MPLS Multi-Topology Identifier Registry
- New Sub-TLV Types for LSP ping: the following new sub-type values under TLV type 1 (Target FEC Stack) have been registered from the "Sub-TLVs for TLV Types 1, 16, and 21" sub-registry within the "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" registry.
Sub-Type Value Field
-------- ------------------
31 MT LDP IPv4 prefix
32 MT LDP IPv6 prefixFigure 12: New Sub-TLV Types for LSP Ping
as highlighted at the end of Section 3.4 ("IGP MT-ID Mapping and Translation"), a new document will be created to detail the policy and process for allocating new MT-ID values 🌟 stay tuned!
10. Manageability Considerations 🛠️
10.1. Control of Function and Policy 🎀
there are capabilities that should be configurable for good manageability. one example is letting people enable or disable the LDP Multi-Topology capability 💅 it's assumed that the mapping of the LDP MT-ID and IGP MT-ID is manually configured on every router by default. if an automatic mapping between IGP MT-IDs and LDP MT-IDs is needed, there must be explicit configuration to do so. no surprise auto-mapping, bestie 🙅♀️
10.2. Information and Data Models 📊
any extensions that might be required for existing MIBs are beyond the scope of this document 🧚
10.3. Liveness Detection and Monitoring 👀
mechanisms defined in this document do not imply any new liveness detection and monitoring requirements. no extra homework here 💖
10.4. Verify Correct Operations 🔍
to debug an LDP-MT-enabled network, you may need to associate the LDP label advertisement with the IGP routing advertisement. in that case, the user MUST understand the mapping mechanism to convert the IGP MT-ID to the LDP MT-ID. the method and type of mapping mechanism is out of scope for this document, so go read up on it 🧠
10.5. Requirements on Other Protocols 🌈
if the LDP MT-ID has an implicit dependency on IGP MT-ID, then the corresponding IGP MT features will need to be supported. so check your IGP side too 🫶
10.6. Impact on Network Operations 🌸
mechanisms defined in this document do not have any impact on network operations. chill 😌
11. Contributors 💜
Ning So
Tata Communications
2613 Fairbourne Cir.
Plano, TX 75082
USA
EMail: ning.so@tatacommunications.com
Raveendra Torvi
Juniper Networks
10 Technology Park Drive
Westford, MA 01886-3140
US
EMail: rtorvi@juniper.net
Huaimo Chen
Huawei Technology
125 Nagog Technology Park
Acton, MA 01719
US
Emily Chen
2717 Seville Blvd, Apt. 1205
Clearwater, FL 33764
US
EMail: emily.chen220@gmail.com
Chen Li
China Mobile
53A, Xibianmennei Ave.
Xunwu District, Beijing 01719
China
EMail: lichenyj@chinamobile.com
Lu Huang
China Mobile
53A, Xibianmennei Ave.
Xunwu District, Beijing 01719
China12. Acknowledgements 🙌
the authors want to thank Dan Tappan, Nabil Bitar, Huang Xin, Eric Rosen, IJsbrand Wijnands, Dimitri Papadimitriou, Yiqun Chai, Pranjal Dutta, George Swallow, Curtis Villamizar, Adrian Farrel, Alia Atlas, and Loa Anderson for their valuable comments on this document 🫶✨
13. References 📚
13.1. Normative References 📚
okay bestie, these are the must-reads. the documents this spec leans on, so you can't really skip them 💅
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
"LDP Specification", RFC 5036, October 2007.
[RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL.
Le Roux, "LDP Capabilities", RFC 5561, July 2009.
[RFC5918] Asati, R., Minei, I., and B. Thomas, "Label Distribution
Protocol (LDP) 'Typed Wildcard' Forward Equivalence Class
(FEC)", RFC 5918, August 2010.
[RFC5919] Asati, R., Mohapatra, P., Chen, E., and B. Thomas,
"Signaling LDP Label Advertisement Completion", RFC 5919,
August 2010.13.2. Informative References 🔍
these ones are extra reading for when you want the deeper lore 🧚 no pressure, but they're iconic
[RFC5920] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[RFC3813] Srinivasan, C., Viswanathan, A., and T. Nadeau,
"Multiprotocol Label Switching (MPLS) Label Switching
Router (LSR) Management Information Base (MIB)", RFC 3813,
June 2004. Srinivasan, C., Viswanathan, A., and T.
Nadeau,
[RFC3815] Cucchiara, J., Sjostrand, H., and J. Luciani, "Definitions
of Managed Objects for the Multiprotocol Label Switching
(MPLS), Label Distribution Protocol (LDP)", RFC 3815, June
2004.Authors' Addresses 🫶
these are the people who made this whole thing happen, so say thank you 💖
Quintin Zhao
Huawei Technology
125 Nagog Technology Park
Acton, MA 01719
US
EMail: quintin.zhao@huawei.com
Kamran Raza
Cisco Systems
2000 Innovation Drive
Kanata, ON K2K-3E8
Canada
EMail: skraza@cisco.com
Chao Zhou
Cisco Systems
300 Beaver Brook Road
Boxborough, MA 01719
US
EMail: czhou@cisco.com
Luyuan Fang
Microsoft
5600 148th Ave NE
Redmond, WA 98052
US
EMail: lufang@microsoft.com
Lianyuan Li
China Mobile
53A, Xibianmennei Ave.
Xunwu District, Beijing 01719
China
EMail: lilianyuan@chinamobile.com
Daniel King
Old Dog Consulting
EMail: daniel@olddog.co.uk📦 where this page comes from
- ietf: rfc7307 2014-07
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms