Update to Include Route Object (IRO) specification in Path Computation Element communication Protocol (PCEP)
draft-ietf-pce-iro-update-06

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.

An informal survey was conducted to determine the state of current and planned implementations with respect to IRO ordering and the 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, based on the survey conclusion and recommendation.

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Update in IRO specification
• 2.1. Update to RFC 5440
• 3. Other 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 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. In order to understand the current usage amongst implementations, a survey of existing and planned implementations was conducted. This survey was informal and conducted via email. Responses were collected and anonymized by the PCE working group chair.

This document updates the IRO specifications in section 7.12 of [RFC5440] as per the conclusion of the survey.

1.1. 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 [RFC2119].

2. Update in 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.

A survey of the existing and planned implementations was conducted in order to understand the current state of usage amongst implementations.

The survey found that most implementations construct or interpret the IRO in an ordered fashion and consider it to be an ordered list. More than half of implementations interpreted the IRO sub-objects as strict hops, others interpreted as loose or supported both interpretation. The results shown in this survey found that most implementations support updating [RFC5440] to specify the IRO as an ordered list and supported the use of the Loose hop bit (L bit) such that both strict and loose hops could be supported in the IRO.

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 -

- The content of IRO is an ordered list of sub-objects representing a series of abstract nodes. An abstract node could be a simple abstract node comprising one node or a group of nodes, for example an AS (comprising of multiple hops within the AS) (refer section 4.3.2 of [RFC3209]).

- The L Bit of 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 Loose bit (L bit) is as per section 4.3.3.1 of [RFC3209].

3. Other Considerations

Based on the survey, it should be noted that most implementations already support this update in the IRO specification. The other implementations are expected to make an update to the IRO procedures based on this document.

During the survey, it was also noted that a minority of the implementations, interpreted 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 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.

Thus it is RECOMMENDED that network operators ensure that all PCEP speakers in their network conform to this document if they intend to use IRO.

4. Security Considerations

This update in 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.

7. References

7.1. Normative References

7.2. Informative References

Author's Address