Softwires D. Hankins
Internet-Draft ISC
Intended status: Standards Track T. Mrugalski
Expires: March 19, 2011 Gdansk University of Technology
September 15, 2010
Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Options for Dual-
Stack Lite
draft-ietf-softwire-ds-lite-tunnel-option-04
Abstract
This document specifies two DHCPv6 options which are 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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Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The Dual-Stack Lite Address DHCPv6 Option . . . . . . . . . . . 3
4. The Dual-Stack Lite Name DHCPv6 Option . . . . . . . . . . . . 4
5. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . . 6
6. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
10. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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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, 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, Fully Qualified Domain Name (FQDN)
or both 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.
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
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message. Client that receives more than one DS-Lite Address option
MUST discard all instances of that option.
The format of the Dual-Stack Lite Address 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) |
| |
| |
+---------------------------------------------------------------+
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 exaclty 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. For more information, see Section 7.2 "High
Availability" of [I-D.softwire-ds-lite].
4. The Dual-Stack Lite Name DHCPv6 Option
The Dual-Stack Lite 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
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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. Any DS-Lite Name option received inside any other option
MUST be ignored.
The DS-Lite Name option MUST NOT appear more than once in a message.
Client that receives more than one DS-Lite Name option MUST discard
all instances of that option.
The format of the Dual-Stack Lite 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_DS_LITE_NAME (TBD) | option-len |
+-------------------------------+-------------------------------+
| tunnel-endpoint-name (FQDN) |
+---------------------------------------------------------------+
option-code: OPTION_DS_LITE_NAME (TBD)
option-len: Length in octets of the tunnel-endpoint-
name field.
tunnel-endpoint-name: A single Fully Qualified Domain Name of the
remote tunnel endpoint, located at the
DS-Lite AFTR.
Figure 2: DS-Lite 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 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. Any possible updates to Section 8 of DHCPv6 [RFC3315] also
apply to encoding of this FQDN field. An example FQDN format for
this option is shown in Figure 3.
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+------+------+------+------+------+------+------+------+------+
| 0x07 | e | x | a | m | p | l | e | 0x03 |
+------+------+------+------+------+------+------+------+------+
| i | s | c | 0x03 | o | r | g | 0x00 |
+------+------+------+------+------+------+------+------+
Figure 3: Example tunnel-endpoint-name.
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 [I-D.softwire-ds-lite].
5. 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.
As a convenience to the operator, the server MAY 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 MUST NOT send either option if it has not been
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explicitly requested by the client.
A DHCPv6 server MUST NOT send more than one DS-Lite Address option.
A DHCPv6 server MUST NOT send more than one DS-Lite Name option.
A DHCPv6 server MUST NOT send DS-Lite Address or DS-Lite Name options
as suboptions in other options.
If the server is configured with an FQDN as the tunnel endpoint
locator, the configured FQDN 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 Name option, so that clients will be able
to ask for DNS servers locations to resolve the domain name provided
in the DS-Lite Name option.
6. 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, 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 and Section 4. The client
(B4) is expected to 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 options, it MUST proceed with resolving the
OPTION_DS_LITE_NAME.
7. 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
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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.
8. 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.
9. Acknowledgements
Authors would like to thank Alain Durand, Rob Austein, Dave Thaler
and Paul Selkirk for their valuable feedback and suggestions.
10. 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.
[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.
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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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