Route Information Options in Redirect Messages
draft-templin-intarea-rio-redirect-00.txt

Abstract

The IPv6 Neighbor Discovery protocol provides a Redirect function allowing routers to inform hosts of a better next hop on the link toward the destination. This document specifies a backward-compatible extension to the Redirect function to allow routers to include forwarding information that the source can associate with the next hop.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on July 10, 2017.

Copyright Notice

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Route Information Options in Redirect Messages
• 3.1. Validation of Redirect Messages
• 3.2. Router Specification
• 3.3. Host Specification
• 4. Implementation Status
• 5. IANA Considerations
• 6. Security Considerations
• 7. Acknowledgements
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Author's Address

1. Introduction

The IPv6 Neighbor Discovery (ND) protocol [RFC2460][RFC4861] provides a Redirect function allowing routers to inform hosts of a better next hop on the link toward the destination. The Redirect message includes a target address identifying the next hop and a destination address taken from the IPv6 packet that triggered the Redirect.

"Default Router Preferences and More-Specific Routes" [RFC4191] specifies a Route Information Option (RIO) that routers can include in Router Advertisement (RA) messages to inform recipients of more-specific routes. This document specifies a backward-compatible extension to allow routers to include RIOs in Redirect messages. This method has precedence in a published experimental RFC [RFC6706].

2. Terminology

The terminology in the normative references applies.

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]. Lower case uses of these words are not to be interpreted as carrying RFC2119 significance.

3. Route Information Options in Redirect Messages

The RIO is specified for inclusion in RA messages in Section 2.3 of [RFC4191]. The IPv6 ND Redirect function is specified in Section 8 of [RFC4861], where the introductory paragraphs include the following:

[RFC4191] and [RFC4861] as discussed in the following sections.

• "Redirect messages are sent by routers to redirect a host to a better first-hop router for a specific destination or to inform hosts that a destination is in fact a neighbor (i.e., on-link)."

This specification permits routers to include RIO options in Redirect messages so that hosts can direct future packets to a better first-hop for a *set of destinations* instead of just a singleton. This specification therefore updates

3.1. Validation of Redirect Messages

The validation of Redirect messages follows Section 8.1 of [RFC4861] which states:

• "The contents of the Reserved field, and of any unrecognized options, MUST be ignored. Future, backward-compatible changes to the protocol may specify the contents of the Reserved field or add new options; "

This specification permits routers to include RIOs in Redirect messages, and therefore represents a backward-compatible change to the protocol through the addition of a new option as described in this passage.

3.2. Router Specification

The Router Specification follows Section 8.2 of [RFC4861], except that RIOs are included in the list of permissible options. Routers therefore MAY send Redirect messages containing RIOs, where the RIOs are determined by a means outside the scope of this specification.

When the router includes RIOs, it MAY set the Destination Address field of the Redirect message to '::' (i.e., the IPv6 unspecified address) if the destination of the packet that triggered the redirection event is covered by a prefix in one of the RIOs.

3.3. Host Specification

The Host Specification follows Section 8.3 of [RFC4861] and Section 3 of [RFC4191]. According to [RFC4861], a host receiving a valid Redirect updates its destination cache and neighbor cache per the Destination and Target information included in the message, respectively. According to [RFC4191], a "Type C" host receiving a valid RA message updates its routing table per the RIOs included in the message.

In light of these considerations, a "Type C" host that receives a Redirect message containing RIOs adopts the combined behaviors of both of these specifications. Namely, the host updates its neighbor cache entry for the Target and updates its routing table per the included RIOs. If the Destination address is not the unspecified address, the host further updates its destination cache.

Note that "Type A'" and "Type B" hosts ignore any RIOs and process the Redirect message according to Section 8.3 of [RFC4861].

4. Implementation Status

The Redirect function and RIOs are widely deployed in IPv6 implementations.

5. IANA Considerations

This document introduces no IANA considerations.

6. Security Considerations

Security considerations for Redirect messages that include RIOs are the same as for any IPv6 ND messages as specified in Section 11 of [RFC4861]. Namely, the protocol must take measures to secure IPv6 ND messages on links where spoofing attacks are possible.

A spoofed Redirect message containing no RIOs could cause corruption in the host's destination cache while a spoofed Redirect message containing RIOs could corrupt the host's routing tables. While the latter would seem to be a more onerous result, the possibility for corruption is unacceptable in either case.

7. Acknowledgements

This document was motivated by discussions on the intarea list.

8. References

8.1. Normative References

8.2. Informative References

Author's Address