Clarification of RRO Node-Id Sub-Object
draft-sitaraman-nodeid-subobject-clarification-00.txt

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Abstract

This document clarifies the RRO format and usage of the node-id sub-object as defined in [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.). The RRO stacking order and allowed formats when including the node-id sub-object is specified.

Table of Contents

1.  Introduction
    1.1.  Terminology
    1.2.  Conventions
2.  PLR Requirements for finding the Merge Point address
3.  RRO Node-id Sub-object formats
    3.1.  RRO stacking order for Node-id Sub-object
4.  Security Considerations
5.  IANA Considerations
6.  Acknowledgments
7.  Normative References
§  Authors' Addresses

1.  Introduction

[RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.) describes the use of the RRO node-id sub-object to find the Merge Point (MP) address for MPLS Fast Reroute [RFC4090] (Pan, P., Swallow, G., and A. Atlas, “Fast Reroute Extensions to RSVP-TE for LSP Tunnels,” May 2005.) in multi-domain networks, where a domain is defined as an Interior Gateway Protocol (IGP) area or an Autonomous System (AS). Finding the MP address using the node-id sub-object for facility backup tunnels is useful to protect inter-domain TE LSPs from a failure of an Area Border Router (ABR) or Autonomous System Border Router (ASBR).

However, [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.) does not define an RRO stacking order when including the node-id sub-object. Therefore different interpretations of the RRO seem acceptable, some of which if allowed do not permit an accurate parsing of the RRO to find the MP address in a multi-domain environment. [RFC3209] (Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, “RSVP-TE: Extensions to RSVP for LSP Tunnels,” December 2001.) provides clear guidelines regarding the order in which sub-objects are pushed on the RRO stack. Such stacking guidelines when pushing a node-id sub-object are required. The lack of a such a guideline can also present interoperability problems between different implementations.

This draft specifies a RRO stacking order when including the node-id sub-object in addition to explaining some of the issues in multi-domain environments.

1.1.  Terminology

The Terminology used in this document is as defined in [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.).

Additionally the following notation is used describe the contents of the Record Route Object:

N = Node-id (node-id sub-object)
I = Interface-address (IPv4 sub-object)
L = Label
| = Marker distinguishing information from neighboring nodes
< > = Order of RRO information from a single node

1.2.  Conventions

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] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

2.  PLR Requirements for finding the Merge Point address

This section discusses the requirements at the PLR for finding the MP address in an inter-domain network in order to create a facility backup tunnel to provide link or node protection.

As described in [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.), the bypass tunnel needs to intersect with the primary tunnel at the MP. The MP address can be found by examining the RRO of the primary tunnel to check if any of the addresses is the MP address. The node-id sub-object was introduced to allow the PLR to pick the MP address in inter-domain environments, where the interface addresses in the RRO of the facility backup and primary tunnel cannot be correlated by the PLR as belonging to the same node (MP). This is specifically true when the PLR and MP are not in the same domain. As [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.) also describes, the problem of finding the MP address within a single IGP area be easily solved since the entire topology information is available.

For example, to provide node protection using facility backup tunnels in the inter-area or inter-AS case to protect from the failure of an ABR or ASBR, the PLR, which is upstream of the failure node must be able to accurately decipher the MP address from the RRO.

Hence, the PLR MUST be able to find the MP address by just parsing the received RRO and not requiring the existence of a Traffic Engineering database in order to provide link or node protection. [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.) was also written with this goal as is implied in its Introduction section though this requirement is not explicitly stated.

3.  RRO Node-id Sub-object formats

When adding the node-id sub-object in the RRO, section 3 of [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.) seems to allow different RRO formats when interpreted along with the RRO definition and usage from [RFC3209] (Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, “RSVP-TE: Extensions to RSVP for LSP Tunnels,” December 2001.).

From section 3 of [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.):

1. Add the node-id sub-object in the RRO carried in an RSVP Resv message and, when required, also add another IPv4/IPv6 sub-object to record interface address.
   
   It seems like the following RRO formats are acceptable:
   
   <N, L>, <N, I, L>, <I, N, L>, <N, L, I>, <I, L, N>
2. Add an IPv4/IPv6 sub-object recording the interface address and, when required, add a node-id sub-object in the RRO.
   
   It seems like the following RRO formats are acceptable:
   
   <I, L, N> though the order of the sub-objects is not specified.

The RRO does not have a defined delimiter using which a node can parse the RRO in the Resv message to find the set of information that has been added by a specific downstream node.

As a result, the PLR might not be able to deterministically find the MP address from the received RRO in the Resv message. The following examples illustrate how the PLR might find it difficult to differentiate between two RRO formats just by parsing the received RRO:

<N, L> | <I, L> | <I, L>
and
<N, L, I, L> | <I, L>

<I, L, N> | <I, L>
and
<I, L> | <N, I, L>

<N, L, I> | <N, L>
and
<N, L> | <I, N, L>

<N, I, L> | <N, L, I, L>
and
<N, I, L> | <N, L> | <I, L>

Using the traffic engineering database to correlate whether an interface and node address received in the RRO belong to the same node is not possible in inter-area or inter-AS environments.

3.1.  RRO stacking order for Node-id Sub-object

The following rules need to be followed by an implementation of [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.):

If the node-id sub-object is included in the RRO, then the IPv4 or IPv6 sub-object MUST also be included. The IPv4 or IPv6 sub-object MUST be pushed onto the RRO prior to pushing on the node-id sub-object. As specified in [RFC3209] (Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, “RSVP-TE: Extensions to RSVP for LSP Tunnels,” December 2001.), if Label_Recording is requested, then the Label Record sub-object is pushed onto the RRO prior to pushing the IP address.

All implementations MUST generate either <N, I, L> or <N, L, I, L> and MUST be able to receive and parse both formats in order to find the MP address. No other formats can be generated by a node when the node-id sub-object needs to be added to the RRO.

In the <N, L, I, L> format, both values of L MUST be identical. The above rules are based on already deployed implementations of [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.).

4.  Security Considerations

No new security issues are introduced beyond those that are described in [RFC4561] (Vasseur, J., Ali, Z., and S. Sivabalan, “Definition of a Record Route Object (RRO) Node-Id Sub-Object,” June 2006.).

5.  IANA Considerations

This draft does not have any request for IANA.

6.  Acknowledgments

The authors would like to thank Miya Kohno, Yakov Rekhter, Avneesh Sachdev and Yasuyuki Matsuoka for their valuable and detailed discussions, reviews and feedback.

7. Normative References

Authors' Addresses