Softwires D. Hankins
Internet-Draft ISC
Intended status: Standards Track T. Mrugalski
Expires: March 31, 2011 Gdansk University of Technology
September 27, 2010
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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This Internet-Draft will expire on March 31, 2011.
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Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The Dual-Stack Lite Address DHCPv6 Option . . . . . . . . . . . 3
4. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . . 4
5. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
9. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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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 [RFC2119].
2. Introduction
Dual-Stack Lite [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 [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
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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.
Figure 1: DS-Lite IPv6 Address DHCPv6 Option Format
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 [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].
4. DHCPv6 Server Behavior
Following requirements are result of applying behaviors defined in
RFC 3315 Section 17.2.2 [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
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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
[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]) 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 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 [RFC3315] discusses DHCPv6-related security issues.
[I-D.softwire-ds-lite] 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.
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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
[I-D.softwire-ds-lite]
Durand, A., Ed., "Dual-stack lite broadband deployments
post IPv4 exhaustion", draft-ietf-softwire-dual-stack-lite
(work in progress).
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
Authors' Addresses
David W. Hankins
Internet Systems Consortium, Inc.
950 Charter Street
Redwood City, CA 94063
US
Phone: +1 650 423 1307
Email: David_Hankins@isc.org
Tomasz Mrugalski
Gdansk University of Technology
Storczykowa 22B/12
Gdansk 80-177
Poland
Phone: +48 698 088 272
Email: tomasz.mrugalski@eti.pg.gda.pl
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