Update to Include Route Object (IRO) specification in Path Computation Element communication Protocol (PCEP)
draft-ietf-pce-iro-update-07

Abstract

The Path Computation Element Communication Protocol (PCEP) provides for communications between a Path Computation Client (PCC) and a PCE, or between two PCEs. RFC 5440 defines the Include Route Object (IRO) to specify network elements to be traversed in the computed path. The specification did not specify if the IRO contains an ordered or un-ordered list of sub-objects. During recent discussions, it was determined that there was a need to define a standard representation to ensure interoperability. It was also noted that there is a benefit in handling of an attribute of the IRO's sub-object, the Loose hop bit (L bit).

This document updates RFC 5440 regarding the IRO specification.

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Table of Contents

• 1. Introduction
• 2. Update in the IRO specification
• 2.1. Update to RFC 5440
• 3. Operational Considerations
• 4. Security Considerations
• 5. IANA Considerations
• 6. Acknowledgments
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Author's Address

1. Introduction

The Path Computation Element Communication Protocol (PCEP) provides for communications between a Path Computation Client (PCC) and a PCE, or between two PCEs. [RFC5440] defines the Include Route Object (IRO) to specify network elements to be traversed in the computed path. The specification did not define if the IRO is an ordered or un-ordered list of sub-objects. In addition, it defined the Loose hop bit (L bit) to have no meaning within an IRO.

[RFC5441] describes the use of an IRO to indicate the sequence of domains to be traversed during inter-domain path computation.

During recent discussions, it was determined that there was a need to define a standard representation to ensure interoperability.

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

2. Update in the IRO specification

Section 7.12 of [RFC5440] describes the IRO as an optional object used to specify a set of network elements to be traversed in the computed path. It stated that the Loose hop bit (L bit) in the sub-object has no meaning within an IRO. It did not mention if the IRO contains an ordered or un-ordered list of sub-objects.

2.1. Update to RFC 5440

Section 7.12 of [RFC5440] regarding the IRO specification is updated to remove the last line in the section 7.12 of [RFC5440], that states :

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

Further, the Section 7.12 of [RFC5440] is updated to add the following two statements at the end of the first paragraph.

- The content of an IRO is an ordered list of sub-objects representing a series of abstract nodes (refer to section 4.3.2 of [RFC3209]).

- The L Bit of an IRO sub-object is set based on the loose or strict hop property of the sub-object; it is set if the sub-object represents a loose hop. If the bit is not set, the sub-object represents a strict hop. The interpretation of the Loose bit (L bit) is as per section 4.3.3.1 of [RFC3209].

3. Operational Considerations

Because of the lack of clarity in [RFC5440], it is possible to encounter implementations that always interpret the IRO sub-objects as loose. When these implementations interwork with an implementation conforming to this document, the following impact might be seen:

• 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 (since the PCC may think of the IRO sub-objects as loose hops, but the PCE interprets 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 does not comply with the requested strict hops (since the PCE interprets them all as loose hops). The PCC may check the returned path and find the issue or it may end up using an incorrect path.

4. Security Considerations

This update in the IRO specification does not introduce any new security considerations, apart from those mentioned in [RFC5440]. Clarification in the supported IRO ordering or Loose hop bit handling will not have any negative security impact.

It is worth noting that PCEP operates over TCP. An analysis of the security issues for routing protocols that use TCP (including PCEP) is provided in [RFC6952].

5. IANA Considerations

This document makes no requests to IANA for action.

6. Acknowledgments

A special thanks to PCE chairs for guidance regarding this work.

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

Thanks to Adrian Farrel for his review and comments.

Thanks to Jonathan Hardwick for document shepherding and providing text in Section 3.

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

Thanks to Peter Yee for Gen-ART review.

Thanks to Alvaro Retana for comments during the IESG review.

7. References

7.1. Normative References

7.2. Informative References

Author's Address