RFC 5330
A Link-Type sub-TLV to Convey the Number of Traffic Engineering Label Switched Paths Signalled with Zero Reserved Bandwidth across a Link
RFC 5330 🎀 A Link-Type sub-TLV to Convey the Number of Traffic Engineering Label Switched Paths Signalled with Zero Reserved Bandwidth across a Link
Network Working Group 🌸 Category: Standards Track 🦋 Date: October 2008
Authors: JP. Vasseur, Ed. (Cisco Systems, Inc), M. Meyer (BT), K. Kumaki (KDDI R&D Labs), A. Bonda (Telecom Italia) 💅
Obsoletes / Updates: This header doesn't list anything it obsoletes or updates ✨
Status of This Memo 💖
okay so this one is an Internet standards track protocol for the Internet community 🫶 It's basically asking everyone to talk about it and send over ideas to make it better. If you want to know where this protocol stands officially, check the current "Internet Official Protocol Standards" (STD 1) list. Distribution of this memo is unlimited, so share it with everyone 💜
Abstract 🌈
Okay, the vibe is that a bunch of Link-type sub-TLVs already exist for OSPF and IS-IS in MPLS Traffic Engineering (TE) 😭 They tell the network stuff like available bandwidth, the TE metric, administrative groups, and so on. Here's the big idea: if you make some statistical guesses about the traffic riding on a set of TE LSPs that were signalled with zero bandwidth (we call those "unconstrained TE LSP" in this doc 🧚), you can design algorithms that load balance those LSPs across equal cost paths. The catch is that you need to know how many unconstrained TE LSPs are signalled across a link. This document creates a brand new Link-type Traffic Engineering sub-TLV to advertise exactly that number ✨
Table of Contents 🍓
1. Introduction ....................................................2
2. Terminology .....................................................3
2.1. Requirements Language ......................................4
3. Protocol Extensions .............................................4
3.1. IS-IS ......................................................4
3.2. OSPF .......................................................4
4. Elements of Procedure ...........................................5
5. IANA Considerations .............................................5
6. Security Considerations .........................................5
7. Acknowledgements ................................................6
8. References ......................................................6
8.1. Normative References .......................................6
8.2. Informative References .....................................61. Introduction 🦋
Honestly, people deploy MPLS Traffic Engineering all the time for fast recovery 🏃♀️💨 They usually lean on a local protection mechanism like MPLS TE Fast Reroute (see [RFC4090]). The usual setup is a full mesh of TE LSPs signalled with zero bandwidth (also called unconstrained TE LSP in this document) between a group of LSRs (Label Switching Routers). Those TE LSPs are protected against link, SRLG (Shared Risk Link Group), and/or node failures using pre-established backup tunnels. The traffic on those unconstrained TE LSPs just follows the IGP shortest path, but it still gets that MPLS TE Fast Reroute protection. Why? Because the path the path computation algorithm (e.g., CSPF) picks is no different from the IGP (Interior Gateway Protocol) shortest path when the TE metric equals the IGP metric 💅
When a reoptimization is triggered for an existing TE LSP, the choice to move it onto a different path comes down to finding a lower cost path that still meets the constraints. Other metrics, like the percentage of reserved bandwidth or the number of hops, can also come into play 🤓 The problem is that metrics like path cost or hop count can be totally useless in some situations. Picture a symmetrical network with ECMPs (Equal Cost Multi-Paths). If the operator uses unconstrained TE LSPs there, the traffic can end up poorly load balanced 😭 Lots of paths between a source and destination can have the same cost, and you can't use the reservable bandwidth on each path as a tie-breaker.
So, by making statistical assumptions about the aggregated traffic on a set of unconstrained TE LSPs, algorithms can load balance (existing or newly configured) unconstrained TE LSPs across equal cost paths. Yep, you guessed it: that needs the number of unconstrained TE LSPs signalled across each link 🧠
Note that the specification of load balancing algorithms is outside the scope of this document and is referred to for the sake of illustration of the motivation for gathering such information.
Knowing how many unconstrained TE LSPs cross each link is useful for other stuff too. For example, you can figure out how many unconstrained TE LSPs would be affected if a link fails 💀
OSPF and IS-IS already have Link-type sub-TLVs for MPLS Traffic Engineering (see [RFC3630] and [RFC5305]). They advertise things like available bandwidth, the traffic engineering metric, administrative group, and so on. But as currently defined in [RFC3630] and [RFC5305], there's no info about the number of unconstrained TE LSPs 🙈 This document fixes that by specifying a new Link-type Traffic Engineering sub-TLV that tells everyone how many unconstrained TE LSPs are signalled across a link.
Unconstrained TE LSPs that are configured and provisioned through a management system MAY be omitted from the count that is reported 🫶
2. Terminology 🧚
Here's the terminology used in this document 📝
CSPF: Constrained Shortest Path First
IGP : Interior Gateway Protocol
LSA: Link State Advertisement
LSP: Link State Packet
MPLS: Multiprotocol Label Switching
LSR: Label Switching Router
SRLG: Shared Risk Link Group
TE LSP: Traffic Engineering Label Switched Path
Unconstrained TE LSP: A TE LSP signalled with a bandwidth equal to 02.1. Requirements Language 🔥
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]. These are the official requirement-level words, so you'll see them capitalized wherever they matter 💅
3. Protocol Extensions 💖
Two Unconstrained TE LSP Count sub-TLVs are defined. Each one specifies the number of TE LSPs signalled with zero bandwidth across a link ✨
3.1. IS-IS 🦋
The IS-IS Unconstrained TE LSP Count sub-TLV is OPTIONAL and MUST NOT appear more than once within the extended IS reachability TLV (type 22) specified in [RFC5305] or the Multi-Topology (MT) Intermediate Systems TLV (type 222) specified in [RFC5120]. If a second instance of the Unconstrained TE LSP Count sub-TLV is present, the receiving system MUST only process the first instance of the sub-TLV. So, one copy only, bestie 🙅♀️
The IS-IS Unconstrained TE LSP Count sub-TLV format is defined below 🎀
Type (1 octet): 23
Length (1 octet): 2
Value (2 octets): number of unconstrained TE LSPs signalled across
the link.3.2. OSPF 🌈
The OSPF Unconstrained TE LSP Count sub-TLV is OPTIONAL and MUST NOT appear more than once within the Link TLV (Type 2). That Link TLV is itself carried within either the Traffic Engineering LSA specified in [RFC3630] or the OSPFv3 Intra-Area-TE LSA (function code 10) defined in [RFC5329]. If a second instance of the Unconstrained TE LSP Count sub-TLV is present, the receiving system MUST only process the first instance of the sub-TLV. Same energy as IS-IS, one and done 💜
The OSPF Unconstrained TE LSP Count sub-TLV format is defined below ✨
Type (2 octets): 23
Length (2 octets): 4
Value (4 octets): number of unconstrained TE LSPs signalled across
the link.4. Elements of Procedure 🧠
If the Unconstrained TE LSP Count sub-TLV is absent, that SHOULD be interpreted as having no information about the link 🤷♀️
Just like the other MPLS Traffic Engineering link characteristics, the triggers for LSA/LSP origination are outside the scope of this document. But be careful: you don't want to trigger a flood of new IS-IS LSPs or OSPF LSAs every time the number of unconstrained TE LSPs changes a tiny bit. Care must be taken to avoid systematic flooding from changes at too fine a granularity 😭⚠️
5. IANA Considerations 🦋
IANA has defined a sub-registry for the sub-TLVs carried in the IS-IS TLV 22. It also assigned a new TLV codepoint for the Unconstrained TE LSP Count sub-TLV carried within TLV 22 👑
Value TLV Name Reference
23 Unconstrained TE LSP Count (sub-)TLV RFC 5330IANA has also defined a sub-registry for the sub-TLVs carried in an OSPF TE Link TLV (type 2). It assigned a new sub-TLV codepoint for the Unconstrained TE LSP Count sub-TLV carried within the TE Link TLV 💅
Value TLV Name Reference
23 Unconstrained TE LSP Count (sub-)TLV RFC 53306. Security Considerations 💀
The function described in this document does not create any new security issues for the OSPF and IS-IS protocols. This is the part where I say it's all fine 🙏 Security considerations for the base OSPF protocol are covered in [RFC2328] and [RFC5340], and for IS-IS they're covered in [RFC1195] and [RFC5304].
A security framework for MPLS and Generalized MPLS can be found in [G/MPLS] 🔒
7. Acknowledgements 🫶
The authors want to give a huge thank you to Jean-Louis Le Roux, Adrian Farrel, Daniel King, Acee Lindem, Lou Berger, Attila Takacs, Pasi Eronen, Russ Housley, Tim Polk, and Loa Anderson for their useful inputs. Literal legends 👑✨
8. References 📚
8.1. Normative References 💜
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
[RFC5304] Li, T. and R. Atkinson, "Intermediate System to
Intermediate System (IS-IS) Cryptographic Authentication",
RFC 5304, October 2008.
[RFC5305] Li, T. and H. Smit, "IS-IS extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3", RFC
5329, September 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.8.2. Informative References 🌸
8.2. Informative References 🔍
Okay, bestie, these are the "for your reading list" references. They're not required to build the thing, but they give you the background. 📚
- [G/MPLS] Fang, L., Ed., "Security Framework for MPLS and GMPLS Networks", Work In Progress, July 2008. 🔐
- [RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May 2005. ⚡
- [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, February 2008. 🗺️
Authors' Addresses 💌
Meet the squad behind this spec! 🫶
JP Vasseur (editor)
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
EMail: jpv@cisco.comMatthew R. Meyer
BT
Boston, MA
USA
EMail: matthew.meyer@bt.comKenji Kumaki
KDDI R&D Laboratories, Inc.
2-1-15 Ohara Fujimino
Saitama 356-8502, JAPAN
EMail: ke-kumaki@kddi.comAlberto Tempia Bonda
Telecom Italia
via G. Reiss Romoli 274
Torino, 10148
ITALIA
EMail: alberto.tempiabonda@telecomitalia.itFull Copyright Statement ⚖️
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