Dynamic Host Configuration Working D. Hankins
Group ISC
Internet-Draft T. Mrugalski
Intended status: Standards Track Gdansk University of Technology
Expires: June 24, 2010 December 21, 2009
Dynamic Host Configuration Protocol (DHCPv6) Options for Dual-Stack Lite
draft-ietf-softwire-ds-lite-tunnel-option-00
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Abstract
This document describes how Dual-Stack Lite configuration (the
Softwire Concentrator (SC)'s address) can be obtained by a Softwire
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Initiator (SI) via DHCPv6.
Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DHCPv6 Options . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. The Dual-Stack Lite Softwire Concentrator Address
Option . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. The Dual-Stack Lite Softwire Concentrator Name Option . . . 4
4. DHCPv6 Server behavior . . . . . . . . . . . . . . . . . . . . 6
5. DHCPv6 Client behavior . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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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-02] 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 Software Initiator 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 Softwire Initiator of the Softwire Concentrator's
location, either an IPv6 address or Fully Qualified Domain Name
(FQDN) may be used. Once this information is conveyed, the presence
of the configuration indicating the Softwire Concentrator's location
also informs a host to initiate Dual-Stack Lite service and become a
Softwire Initiator.
To provide the conveyance of the configuration information, two
DHCPv6 [RFC3315] options are used; one in the case where the host
receives an IPv6 address, and one in the case where the host receives
an FQDN in order to derive an IPv6 address.
3. DHCPv6 Options
Following sections define two new DHCPv6 options, conformant with
requirements specified in DHCPv6 [RFC3315] Section 22.1.
3.1. The Dual-Stack Lite Softwire Concentrator Address Option
The Dual-Stack Lite Softwire Concentrator 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 (DS-Lite
Address Family Transition Router element).
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.
The DS Lite Address option MUST NOT appear more than once in a
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message.
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) |
| |
| |
+---------------------------------------------------------------+
DS Lite IPv6 Address option format.
Figure 1
option-code: OPTION_DS_LITE_ADDR (TBD)
option-len: Length of the tunnel-endpoint-addr field, which is
currently defined to be precisely 16 octets.
tunnel-endpoint-addr: This field contains a single IPv6 address in
binary representation of the remote tunnel endpoint, located at
the DS-Lite AFTR. It is precisely 16 octets in length.
The client validates the DS-Lite Address option by confirming the
option is of 16 octets in length or greater. The client MUST ignore
tunnel-endpoint-addr shorter than 16 octets. In the event the option
is greater than 16 octets in length, only the first 16 octets are
intrepreted.
Because this option conveys the tunnel-endpoint-addr value, no
further processing is required of the client.
3.2. The Dual-Stack Lite Softwire Concentrator Name Option
The Dual-Stack Lite Softwire Concentrator Name Option consists of
option-code and option-len fields (common for all DHCPv6 options),
and a variable length tunnel-endpoint-name field, containing a Fully
Qualified Domain Name that refers to the AFTR (DS-Lite Address Family
Transition Router element) the client is requested to establish a
connection with.
The DS Lite 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.
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The DS Lite Name option MUST NOT appear more than once in a message.
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_NAME (TBD) | option-len |
+-------------------------------+-------------------------------+
| tunnel-endpoint-name (FQDN) |
+---------------------------------------------------------------+
DS Lite FQDN option format.
Figure 2
option-code: OPTION_DS_LITE_NAME (TBD)
option-len: Length in octets of the tunnel-endpoint-name field.
tunnel-endpoint-name: This field contains a single Fully Qualified
Domain Name of the remote tunnel endpoint, located at the DS-Lite
AFTR.
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 64 octets), followed by
the label. This repeats until all labels in the FQDN are exhausted.
The root label (or the end of the FQDN) is denoted as a zero length
label. An example FQDN format for this option is shown in Figure 3.
+------+------+------+------+------+------+------+------+------+
| 0x07 | e | x | a | m | p | l | e | 0x03 |
+------+------+------+------+------+------+------+------+------+
| i | s | c | 0x03 | o | r | g | 0x00 |
+------+------+------+------+------+------+------+------+
Example tunnel-endpoint-name.
Figure 3
Note that in the specific case of the example tunnel-endpoint-name,
(Figure 3) the length of the option is 17 octets, and so an option-
len field value of 17 would be used.
The client validates the option in this format by first confirming
that the option length 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), and that the tunnel-endpoint-name is of
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valid format as described in DHCPv6 Section 8 [RFC3315]; there are no
compression tags, there is at least one label of nonzero length.
The client determines a value for the tunnel-endpoint-addr from the
tunnel-endpoint-name using standard DNS resolution, as defined in
[RFC3596]. If the 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
[draft-ietf-softwire-dual-stack-lite-02].
4. DHCPv6 Server behavior
DHCP servers must translate user input from their own specific and
unique operator's interfaces into configuration state for the client.
The server MUST provide a way to configure the OPTION_DS_LITE_ADDR,
and SHOULD allow the operator to enter a Fully Qualified Domain Name,
upon which the server performs DNS Resolution to assemble its
OPTION_DS_LITE_ADDR contents. The server MAY either provide the same
Fully Qualified Domain Name as OPTION_DS_LITE_NAME contents, or
simply provide a distinct method of configuring it.
If configured with values, DHCPv6 servers will include the DS Lite
Address and/or Name options if either or both appear 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 MAY NOT send either option if it has not been
explicitly requested by the client.
If the server is configured with an FQDN as the tunnel endpoint
locator, the configured FDQN value must contain a resolvable Fully
Qualified Domain Name, having appropriate delegations from the root,
and having a AAAA record locating the Softwire Concentrator.
If OPTION_DS_LITE_NAME is being configured, it is RECOMMENDED that
the server also be configured to provide OPTION_DNS_SERVERS defined
in [RFC3646] together with the DS Lite option, so that clients will
be able to ask for DNS servers locations to resolve the domain name
provided in the DS Lite option.
5. DHCPv6 Client behavior
A client that supports B4 functionality of the DS Lite (defined in
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[draft-ietf-softwire-dual-stack-lite-02]) MUST include
OPTION_DS_LITE_ADDR on its OPTION_ORO, and MAY include
OPTION_DS_LITE_NAME at its option and ability.
If requesting the OPTION_DS_LITE_NAME option, the client also SHOULD
request OPTION_DNS_SERVERS defined in [RFC3646] to be able to resolve
any received domain name.
If the client receives either DS Lite Option, it MUST verify the
option contents as described in Section 3.1 and Section 3.2. The
client SHOULD establish a softwire tunnel to the tunnel-endpoint-addr
IPv6 address it determines from either of these options.
If the client requests and receives both the OPTION_DS_LITE_ADDR and
the OPTION_DS_LITE_NAME, it MUST proceed with resolving the
OPTION_DS_LITE_NAME.
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.
[draft-ietf-softwire-dual-stack-lite-02] discusses DS Lite related
security issues.
7. IANA Considerations
IANA is requested to allocate two DHCPv6 Option codes referencing
this document. One delineating OPTION_DS_LITE_ADDR, and one
delineating OPTION_DS_LITE_NAME.
8. Acknowledgements
Authors would like to thank Alain Durand, Rob Austein and Dave Thaler
for their valuable feedback and suggestions.
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9. Normative References
[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.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", RFC 3596,
October 2003.
[RFC3646] Droms, R., "DNS Configuration options for Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
December 2003.
[draft-ietf-softwire-dual-stack-lite-02]
Durand, A., Ed., "Dual-stack lite broadband deployments
post IPv4 exhaustion", October 2009.
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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