Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Option for Dual-Stack Lite
draft-ietf-softwire-ds-lite-tunnel-option-05

Abstract

This document specifies single DHCPv6 option which is meant to be used by a Dual-Stack Lite client (Basic Bridging BroadBand element, B4) to discover its Address Family Transition Router (AFTR) address.

Status of this Memo

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Copyright Notice

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Table of Contents

1.  Requirements Language
2.  Introduction
3.  The Dual-Stack Lite Address DHCPv6 Option
4.  DHCPv6 Server Behavior
5.  DHCPv6 Client Behavior
6.  Security Considerations
7.  IANA Considerations
8.  Acknowledgements
9.  Normative References
§  Authors' Addresses

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 RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

2.  Introduction

Dual-Stack Lite (Durand, A., Ed., “Dual-stack lite broadband deployments post IPv4 exhaustion,” .) [I‑D.softwire‑ds‑lite] is a solution to offer both IPv4 and IPv6 connectivity to customers which are addressed only with an IPv6 prefix (no IPv4 address is assigned to the attachment device). One of its key components is an IPv4-over-IPv6 tunnel, commonly referred to as a Softwire. DS-Lite Basic Bridging BroadBand (B4) will not know if the network it is attached to offers Dual-Stack Lite support, and if it did would not know the remote end of the tunnel to establish a connection.

To inform the B4 of the Address Family Transition Router's (AFTR) location, an option containing a single IPv6 address may be used. Once this information is conveyed, the presence of the configuration indicating the AFTR's location also informs a host to initiate Dual-Stack Lite (DS-Lite) service and become a Softwire Initiator.

To provide the conveyance of the configuration information, a single DHCPv6 (Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, “Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” July 2003.) [RFC3315] option is used.

The details of how the B4 establishes an IPv4-in-IPv6 tunnel to the AFTR are out of scope for this document.

3.  The Dual-Stack Lite Address DHCPv6 Option

The Dual-Stack Lite Address option consists of option-code and option-len fields (common for all DHCPv6 options), and a 128 bit tunnel-endpoint-addr field, containing one IPv6 address. The tunnel-endpoint-addr specifies the location of the remote tunnel endpoint, expected to be located at an AFTR.

The DS-Lite Address option MAY appear in the root scope of a DHCPv6 packet. It MUST NOT appear inside any IA_NA, IA_TA, IA_PD, IAADDR, or similar. Any DS-Lite Address option received inside any other option MUST be ignored.

The DS-Lite Address option MUST NOT appear more than once in a message.

The format of the Dual-Stack Lite Address option is shown in the following figure:

     0                   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_DS_LITE_ADDR (TBD)   |         option-len: 16        |
    +-------------------------------+-------------------------------+
    |                                                               |
    |               tunnel-endpoint-addr (IPv6 Address)             |
    |                                                               |
    |                                                               |
    +---------------------------------------------------------------+

             option-code: OPTION_DS_LITE_ADDR (TBD)

              option-len: Length of the tunnel-endpoint-addr field,
                          which is precisely 16 octets.

    tunnel-endpoint-addr: A single IPv6 address in binary
                          representation of the remote tunnel
                          endpoint, located at the DS-Lite AFTR.

The client validates the DS-Lite Address option by confirming the option length is exactly 16 octets. The client MUST ignore any DS-Lite Address option that has length other than 16 octets.

Because this option conveys the tunnel-endpoint-addr value, no further processing is required of the client.

This option conveys a single IPv6 address, as the Dual-Stack Lite specification (Durand, A., Ed., “Dual-stack lite broadband deployments post IPv4 exhaustion,” .) [I‑D.softwire‑ds‑lite] defines only one Softwire connection between a B4 and any AFTR. Multiple connections or endpoints are undefined. It is expected that Service Provider (SP) will deal with load balancing and high availability, not the client. For more information, see Section 12.3 "High Availability" of [I‑D.softwire‑ds‑lite] (Durand, A., Ed., “Dual-stack lite broadband deployments post IPv4 exhaustion,” .).

4.  DHCPv6 Server Behavior

Following requirements are result of applying behaviors defined in RFC 3315 Section 17.2.2 (Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, “Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” July 2003.) [RFC3315] to the DS-Lite Address option. They do not change default DHCPv6 operation, but rather are enumerated here as a convenience for the reader.

If configured to offer DS-Lite Address information, DHCPv6 server will include the DS-Lite Address option if such option appears on the client's Option Request Option (OPTION_ORO). RFC 3315 Section 17.2.2 (Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, “Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” July 2003.) [RFC3315] describes how a DHCPv6 client and server negotiate configuration values using the ORO.

A DHCPv6 server MUST NOT send DS-Lite Address option if it has not been explicitly requested by the client.

A DHCPv6 server MUST NOT send more than one DS-Lite Address option.

A DHCPv6 server MUST NOT send DS-Lite Address as suboption in other options.

5.  DHCPv6 Client Behavior

A client that supports B4 functionality of DS-Lite (defined in [I‑D.softwire‑ds‑lite] (Durand, A., Ed., “Dual-stack lite broadband deployments post IPv4 exhaustion,” .)) and conforms to this specification MUST include OPTION_DS_LITE_ADDR on its OPTION_ORO.

If the client receives DS-Lite Address option, it MUST verify the option contents as described in Section 3 (The Dual-Stack Lite Address DHCPv6 Option). The client (B4) is expected to establish a softwire tunnel to the tunnel-endpoint-addr IPv6 address it determines from DS-Lite Address option.

Client that receives more than one DS-Lite Address option MUST discard all instances of that option.

6.  Security Considerations

This document does not present any new security issues, but as with all DHCPv6-derived configuration state, it is completely possible that the configuration is being delivered by a third party (Man In The Middle). As such, there is no basis to trust that the access the DS-Lite Softwire connection represents can be trusted, and it should not therefore bypass any security mechanisms such as IP firewalls.

RFC 3315 (Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, “Dynamic Host Configuration Protocol for IPv6 (DHCPv6),” July 2003.) [RFC3315] discusses DHCPv6-related security issues.

[I‑D.softwire‑ds‑lite] (Durand, A., Ed., “Dual-stack lite broadband deployments post IPv4 exhaustion,” .) discusses DS-Lite related security issues.

7.  IANA Considerations

IANA is requested to allocate single DHCPv6 option code referencing this document, delineating OPTION_DS_LITE_ADDR name.

8.  Acknowledgements

Authors would like to thank Alain Durand, Rob Austein, Dave Thaler, Paul Selkirk and Ralph Droms for their valuable feedback and suggestions.

This work has been partially supported by the Polish Ministry of Science and Higher Education under the European Regional Development Fund, Grant No. POIG.01.01.02-00-045/09-00 (Future Internet Engineering Project).

9. Normative References

Authors' Addresses