Carrying an Identifier in IPv6 packets

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Table of Contents

1. Introduction

Some recent use cases have a need for carrying an identifier in IPv6 packets. Two examples are [I-D.draft-ietf-6man-enhanced-vpn-vtn-id] and [I-D.draft-li-6man-topology-id]. While those drafts might perfectly make sense on their own, each document requires IANA to allocate a new code point for a new option, and so for very similar situations, which could quickly exhaust the allocation space if similar designs are proposed in the future. As an example, one might need an 8-bit ID, while another one might need a 32-bit, 64-bit or 128-bit ID. Or, even worse, one might need a 32-bit ID in a specific context, while someone else might also need a 32-bit ID in another context. Therefore, allocating a new code point for each similar option is probably not the way to go.¶

This document proposes two different solutions to carry an identifier in IPv6 packets, in order to avoid the aforementioned issue. Each solution defines a new option in the Destination Options and Hop-by-Hop Options sub-registry. Both are explained in this document.¶

2. Conventions and Definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

3. Solution 1: Generic Identifier

For simple use cases such as a single identifier carried without additional fields and without specific context, a new Option Type named "Generic Identifier" is defined as follows:¶

                         1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                    |  Option Type  |  Opt Data Len |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                  Identifier (variable length)                 ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 1. Generic Identifier Option

where:¶

• Option Type: 8-bit option type as defined in Section 5.1.¶
• Opt Data Len: 8-bit unsigned integer. Length of the Identifier field, in octets.¶
• Identifier: variable length field representing the carried identifier.¶

4. Solution 2: Identifier with Context

For use cases where one or several identifiers are carried with additional fields, or when a context is required, a new Option Type named "Identifier with Context" is defined as follows:¶

                         1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                    |  Option Type  |  Opt Data Len |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          Context-ID           |           Reserved            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                Context-Data (variable length)                 ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 2. Identifier with Context Option

where:¶

• Option Type: 8-bit option type as defined in Section 5.2.¶
• Opt Data Len: 8-bit unsigned integer. Length of this option, in octets, not including the first 2 octets.¶
• Context-ID: 16-bit field as defined in Section 5.2.1.¶
• Reserved: 16-bit field MUST be set to zero upon transmission and ignored upon reception.¶
• Context-Data: variable length field representing a data structure which depends on the Context-ID field.¶

5. IANA Considerations

    Binary Value   Description                     Reference
    act chg rest
    --------------------------------------------------------------
    00   0  TBD    Generic Identifier Option       [This document]

    Binary Value   Description                     Reference
    act chg rest
    --------------------------------------------------------------
    00   0  TBD    Identifier with Context Option  [This document]

    Code point       Description             Reference
    +--------+--------------------------+-----------------+
    | 0x0000 |         Reserved         |  This document  |
    +--------+--------------------------+-----------------+
    | 0x0001 |                          |                 |
    |  ....  |        Unassigned        |                 |
    | 0xffef |                          |                 |
    +--------+--------------------------+-----------------+
    | 0xfff0 |                          |                 |
    |  ....  | RFC3692-style Experiment |    [RFC8126]    |
    | 0xfffe |                          |                 |
    +--------+--------------------------+-----------------+
    | 0xffff |         Reserved         |  This document  |
    +--------+--------------------------+-----------------+

6. Security Considerations

As this document describes new options for IPv6, these are similar to the security considerations of [RFC8200] and the weakness documented in [RFC8250].¶

This document does not define security considerations for the Context-Data field of the Identifier with Context Option, which varies based on the Context-ID. These custom data structures will have security considerations in their own documents that define the new formats.¶

Acknowledgments

Author's Address