Softwires D. Hankins
Internet-Draft Google
Intended status: Standards Track T. Mrugalski
Expires: June 2, 2011 Gdansk University of Technology
November 29, 2010
Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Option for Dual-
Stack Lite
draft-ietf-softwire-ds-lite-tunnel-option-06
Abstract
This document specifies a 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
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on June 2, 2011.
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Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The AFTR-Name DHCPv6 Option . . . . . . . . . . . . . . . . . . 3
4. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . . 5
5. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
9. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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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. A DS-Lite "Basic Bridging
BroadBand" (B4) device 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, a DNS [RFC1035] hostname 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, expressing the AFTR's Fully
Qualified Domain Name to the B4 element.
The details of how the B4 establishes an IPv4-in-IPv6 tunnel to the
AFTR are out of scope for this document.
3. The AFTR-Name DHCPv6 Option
The AFTR-Name option consists of option-code and option-len fields
(as all DHCPv6 options have), and a variable length tunnel-endpoint-
name field containing a fully qualified domain name that refers to
the AFTR which the client is asked to connect to.
The OPTION_AFTR_NAME 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 OPTION_AFTR_NAME option received inside any other
option MUST be ignored.
The OPTION_AFTR_NAME option MUST NOT appear more than once in a
message. Clients that receive more than one OPTION_AFTR_NAME options
MUST discard all instances of that option, acting as if none were
sent.
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The format of the AFTR-Name 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_AFTR_NAME: (TBD) | option-len |
+-------------------------------+-------------------------------+
| |
| tunnel-endpoint-name (FQDN) |
| |
+---------------------------------------------------------------+
OPTION_AFTR_NAME: (TBD)
option-len: Length of the tunnel-endpoint-name field.
tunnel-endpoint-name: A fully qualified domain name identifying
the tunnel endpoint, located at the DS-Lite
AFTR.
Figure 1: AFTR-Name DHCPv6 Option Format
The tunnel-endpoint-name field is formatted as required in DHCPv6
[RFC3315] Section 8 ("Representation and Use of Domain Names").
Briefly, the format described is using a single octet noting the
length of one DNS label (limited to at most 63 octets), followed by
the label contents. This repeats until all labels in the FQDN are
exhausted, including a terminating zero-length label. Any updates to
Section 8 of DHCPv6 [RFC3315] also apply to encoding of this field.
An example format for this option is shown in Figure 2, which conveys
the FQDN "aftr.example.com.".
+------+------+------+------+------+------+------+------+------+
| 0x04 | a | f | t | r | 0x07 | e | x | a |
+------+------+------+------+------+------+------+------+------+
| m | p | l | e | 0x03 | c | o | m | 0x00 |
+------+------+------+------+------+------+------+------+------+
Figure 2: Example tunnel-endpoint-name.
Note that in the specific case of the example tunnel-endpoint-name,
(Figure 2) the length of the tunnel-endpoint-name is 18 octets, and
so an option-len field value of 18 would be used.
The option is validated by confirming that the option-len is greater
than 3, that the option data can be contained by the option length
(that the option length does not run off the end of the packet), that
individual label lengths do not exceed the option length, and that
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the tunnel-endpoint-name is of valid format as described in DHCPv6
Section 8 [RFC3315]; there are no compression tags, there is at least
one label of nonzero length.
4. DHCPv6 Server Behavior
A DHCPv6 server MUST NOT send more than one OPTION_AFTR_NAME option.
A DHCPv6 server MUST NOT send the OPTION_AFTR_NAME option as a
suboption in other options; it MUST appear only in the root scope of
any DHCPv6 messages made in response to clients (Reply, Advertise, et
al).
RFC 3315 Section 17.2.2 [RFC3315] describes how a DHCPv6 client and
server negotiate configuration values using the Option Request Option
(OPTION_ORO). As a convenience to the reader, we mention here that a
server will not reply with a value for the OPTION_AFTR_NAME if the
client has not explicitly enumerated it on its OPTION_ORO.
5. DHCPv6 Client Behavior
A client that supports the B4 functionality of DS-Lite (defined in
[I-D.softwire-ds-lite]) and conforms to this specification MUST
include OPTION_AFTR_NAME on its OPTION_ORO.
Because it requires DNS name to address resolution, a client MAY also
wish to include the OPTION_DNS_SERVERS option on its OPTION_ORO.
If the client receives the OPTION_AFTR_NAME option, it MUST verify
the option contents as described in Section 3.
If the client receives more than one OPTION_AFTR_NAME option, it MUST
discard all instances of that option.
The client performs standard DNS resolution using the provided FQDN
to resolve a AAAA record, as defined in [RFC3596] and STD 13
[RFC1034] [RFC1035].
If any DNS response contains more than one IPv6 address, the client
picks only one IPv6 address and uses it as a remote tunnel endpoint.
The client MUST NOT establish more than one DS-Lite tunnel at the
same time. For a redundancy and high availability discussion, see
Section 7.2 "High availability" of [I-D.softwire-ds-lite].
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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_AFTR_NAME.
8. Acknowledgements
Authors would like to thank Alain Durand, Rob Austein, Dave Thaler,
Paul Selkirk, Ralph Droms, Mohamed Boucadair and Maglione Roberta 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).
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[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.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", RFC 3596,
October 2003.
Authors' Addresses
David W. Hankins
Google, Inc.
1600 Amphitheatre Parkway
Mountain View, CA 94043
USA
Email: dhankins@google.com
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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