Dynamic Host Configuration Working D. Hankins
Group ISC
Internet-Draft T. Mrugalski
Intended status: Standards Track Gdansk University of Technology
Expires: July 9, 2010 January 5, 2010
Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Options for Dual-
Stack Lite
draft-ietf-softwire-ds-lite-tunnel-option-01
Abstract
This document specifies two DHCPv6 Options which are meant to be used
by Softwire Initiator (SI) to retrieve its attached DS-Lite AFTR
(Address Family Transition Router).
Status of this Memo
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Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. DHCPv6 Options . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. The Dual-Stack Lite Softwire Concentrator Address
DHCPv6 Option . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. The Dual-Stack Lite Softwire Concentrator Name DHCPv6
Option . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . . 6
5. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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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
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, but a 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, 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 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, 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.
This document assumes that the SI is provided with appropriate
instructions for the activation of an IPv4-in-IPv6 scheme which is
supposed to be supported in both B4 and AFTR. Consequently, this
memo does not precise the IPv4-in-IPv6 encapsulation scheme to be
used by B4.
3. DHCPv6 Options
Following sub-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 DHCPv6 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
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remote tunnel endpoint, expected to be located at an AFTR (DS-Lite
Address Family Transition Router element).
The DS-Lite Address DHCPv6 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 DHCPv6 Option MUST NOT appear more than once in a
message.
The format of the Dual-Stack Lite Softwire Concentrator Addr DHCPv6
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) |
| |
| |
+---------------------------------------------------------------+
DS Lite IPv6 Address DHCPv6 Option format.
Figure 1
Below is provided the description of the enclosed fields:
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 DHCPv6 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 interpreted.
Because this option conveys the tunnel-endpoint-addr value, no
further processing is required of the client.
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The definition of this option is simple and encloses only a single
IPv6 address. It is temping to define a flexible option which may
convey several IPv6 addresses (for robustness and service
availability reasons), but for the sake of simplicity and consistency
it is recommended to use a FQDN Option instead of conveying several
IPv6 addresses.
3.2. The Dual-Stack Lite Softwire Concentrator Name DHCPv6 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 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.
The DS-Lite Name DHCPv6 Option MUST NOT appear more than once in a
message.
The format of the Dual-Stack Lite Softwire Concentrator Name DHCPv6
Option is shown in th 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_NAME (TBD) | option-len |
+-------------------------------+-------------------------------+
| tunnel-endpoint-name (FQDN) |
+---------------------------------------------------------------+
DS-Lite FQDN DHCPv6 Option format.
Figure 2
Below is provided the description of the enclosed fields:
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
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[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 (B4) 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 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 (B4) 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
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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, the server MUST 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 Name DHCPv6 option.
5. DHCPv6 Client Behavior
A client that supports B4 functionality of the DS-Lite (defined in
[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 DHCPv6 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 (B4) 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
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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.
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.
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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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