RFC 7896

Update to the Include Route Object (IRO) Specification in the Path Computation Element Communication Protocol (PCEP) ✨

Okay bestie, here's the title block tea 🫖💅. This is RFC 7896, written by D. Dhody of Huawei Technologies, dated June 2016. It's a Standards Track document (the ISSN is 2070-1721), and it updates RFC 5440 🎀. It doesn't obsolete anything.

Here's the vibe: PCEP lets a PCC and a PCE talk, or two PCEs talk to each other 🦋. RFC 5440 gave us the Include Route Object (IRO) to list the network elements a computed path has to go through, but it never said whether the IRO is an ordered or unordered list. Plus, it said the L bit had no meaning inside an IRO, which is kinda messy 🙈. This doc fixes both things so implementations can actually interoperate 🫶.

1. Introduction 🌸

PCEP is the protocol for PCC-to-PCE and PCE-to-PCE chats 💜. [RFC5440] defines the IRO for specifying the network elements to traverse in the computed path. The spec just doesn't say if the IRO is ordered or unordered, and it says the L bit means nothing in there 😭.

[RFC5441] shows how you use an IRO to indicate the sequence of domains for inter-domain path computation, which is giving main character energy 👑.

The group realized they needed a standard representation so everyone's on the same page, so interoperability isn't a vibe check 🍓.

This document updates the IRO specifications in Section 7.12 of [RFC5440] ✨.

2. Update in the IRO Specification 🧚

Section 7.12 of [RFC5440] says the IRO is an optional object used to specify a set of network elements to traverse in the computed path. It says the L bit in the subobject has no meaning inside an IRO 💀. It doesn't say whether the IRO is ordered or unordered, so yeah, that's the gap we're filling 🔥.

2.1. Update to RFC 5440 💖

The IRO specification gets updated by removing the last line of Section 7.12 of [RFC5440], which currently reads:

"The L bit of such sub-object has no meaning within an IRO."

Also, Section 7.12 of [RFC5440] gets two new statements added at the end of its first paragraph 🌈:

• The content of an IRO is an ordered list of subobjects representing a series of abstract nodes (refer to Section 4.3.2 of [RFC3209]).
• The L bit of an IRO subobject is set based on the loose or strict hop property of the subobject. It is set if the subobject represents a loose hop. If the bit is not set, the subobject represents a strict hop. The interpretation of the L bit is as per Section 4.3.3.1 of [RFC3209] 🦋.

3. Operational Considerations 🎀

Because [RFC5440] was kinda unclear, you might run into implementations that always treat IRO subobjects as loose hops 😬. When those interwork with an implementation following this document, these things might happen:

• If a non-conforming (to this document) PCC sends an IRO to a conforming (to this document) PCE, then the PCE may unexpectedly fail to find a path. The PCC may think the IRO subobjects are loose hops, but the PCE reads them as strict hops 🙃.
• If a conforming PCC sends an IRO containing strict hops to a non-conforming PCE, then the PCE may erroneously return a path that doesn't comply with the requested strict hops, since the PCE reads them all as loose hops 🚨. The PCC may check the returned path and catch the issue, or it may end up using an incorrect path 😱.

4. Security Considerations 🔐

This update to the IRO specification does not introduce any new security considerations, apart from the ones already mentioned in [RFC5440]. Clarifying the supported IRO ordering or the Loose hop bit handling won't have any negative security impact ✨.

Worth noting though: PCEP runs over TCP. An analysis of the security issues for routing protocols that use TCP (including PCEP) is provided in [RFC6952] 🛡️.

5. References 📚

5.1. Normative References 💜

[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, <http://www.rfc-editor.org/info/rfc3209>.

[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, <http://www.rfc-editor.org/info/rfc5440>.

5.2. Informative References 🌷

[RFC5441] Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux, "A Backward-Recursive PCE-Based Computation (BRPC) Procedure to Compute Shortest Constrained Inter-Domain Traffic Engineering Label Switched Paths", RFC 5441, DOI 10.17487/RFC5441, April 2009, <http://www.rfc-editor.org/info/rfc5441>.

[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of BGP, LDP, PCEP, and MSDP Issues According to the Keying and Authentication for Routing Protocols (KARP) Design Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013, <http://www.rfc-editor.org/info/rfc6952>.

Acknowledgments 🫶

Special thanks to the PCE chairs for guidance on this work 👑.

Thanks to Francesco Fondelli for suggestions clarifying the L bit usage 💅.

Thanks to Adrian Farrel for the review and comments 🌸.

Thanks to Jonathan Hardwick for shepherding the document and writing the text in Section 3 🧚.

Thanks to Deborah Brungard for comments and for being the responsible AD 🦋.

Thanks to Peter Yee for the Gen-ART review 💖.

Thanks to Alvaro Retana for comments during the IESG review 🙌.

Author's Address 📮

Dhruv Dhody Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka 560066 India

Email: dhruv.ietf@gmail.com