Dynamic Host Configuration Working D. Hankins
Group ISC
Internet-Draft March 23, 2009
Intended status: Standards Track
Expires: September 24, 2009
Dynamic Host Configuration Protocol Option for Dual-Stack Lite
draft-dhankins-softwire-tunnel-option-03
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 24, 2009.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
This document describes how Dual-Stack Lite configuration (the
Softwire Concentrator (SC)'s address) can be obtained by a Softwire
Hankins Expires September 24, 2009 [Page 1]
Internet-Draft DS Lite Option March 2009
Initiator (SI) via DHCPv6.
Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The Dual-Stack Lite DHCPv6 Option . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5
Hankins Expires September 24, 2009 [Page 2]
Internet-Draft DS Lite Option March 2009
1. Requirements Language
In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL",
"RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in BCP 14, RFC 2119 [RFC2119].
2. Introduction
Dual-Stack Lite [draft-ietf-softwire-dual-stack-lite-00] is a method
to extend IPv4 access to an IPv6-only addressed host. One of its key
components is an IPv4-over-IPv6 tunnel, commonly referred to as a
Softwire, but a host 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.
These are two separate pieces of information; 1) Should I shut down
my dual-stack IPv4 side, and use the softwire exclusively for IPv4
access? 2) At what IPv6 address should I establish a softwire
connection?
These two questions can be answered with one DHCPv6 [RFC3315] option.
DISCUSSION: It can be argued that if you inform a client it should
perform Dual-Stack Lite, but fail to deliver an IPv6 tunnel endpoint,
then its IPv4 access is certainly broken. If you give the client an
IPv6 tunnel endpoint but fail to inform it that it must use Dual-
Stack Lite for IPv4 access, then again its access is likely broken,
or is operating in a degraded mode of service (if an operator offers
a Dual-Stack Lite method of access, there either isn't any native
IPv4 access, or the Dual-Stack Lite method works better than native
access - if a network had better native IPv4 access than Dual-Stack
Lite access, there would be no reason to extend the service). So the
presence of a tunnel address also indicates the intent to use it.
3. The Dual-Stack Lite DHCPv6 Option
The Dual-Stack Lite DHCPv6 Option is simply an IPv6 address.
Hankins Expires September 24, 2009 [Page 3]
Internet-Draft DS Lite Option March 2009
The Dual-Stack Lite Option Format follows:
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 (TBD) | length (16) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The code for this option is TBD. The length is precisely 16. The
IPv6 Address field is an IPv6 address.
The DS Lite 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.
If configured with a value, DHCPv6 servers will include the Softwires
option if it 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 client that supports DS Lite MUST include OPTION_DS_LITE on its
OPTION_ORO. There is no reasonable expectation that a server will
reply with the DS Lite option if it has not been requested.
If the client receives a DS Lite Option, it MUST verify the option
length is precisely 16 octets, and ignore the option otherwise.
Provided it is of valid length, the client SHOULD terminate or
withdraw any DHCPv4 [RFC2131] configuration on the same interface.
If DHCPv4 configuration has concluded, the client SHOULD perform a
DHCPRELEASE as it tears down its IPv4 configuration. The client
SHOULD establish a softwire tunnel to the included IPv6 address.
DISCUSSION: The author's best understanding of the current
epistemology on IPv6 multihoming is that the client will have IPv6
addresses on multiple different IPv6 prefixes. If a host is
multihomed, then, it is strange enough to wonder how DHCPv6
configuration will work as most DHCPv6 clients will attach to only
one DHCPv6 server. It is even stranger to wonder how the client
would react if all of its multiple homes wished to provide IPv4
access via DS Lite. Would a client establish more than one tunnel?
Perhaps this option should permit multiple IPv6 addresses?
Hankins Expires September 24, 2009 [Page 4]
Internet-Draft DS Lite Option March 2009
4. 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.
5. IANA Considerations
IANA is requested to allocate one DHCPv6 Option code, referencing
this document.
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, 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.
[draft-ietf-softwire-dual-stack-lite-00]
Durand, A., Droms, R., Haberman, B., and J. Woodyatt,
"Dual-stack lite broadband deployments post IPv4
exhaustion", March 2009.
Author's Address
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
Hankins Expires September 24, 2009 [Page 5]