Network Working Group F. Xia
Internet-Draft B. Sarikaya
Expires: August 18, 2008 Huawei USA
February 15, 2008
Usage of Host Generating Interface Identifier in DHCPv6
draft-xia-dhc-host-gen-id-00.txt
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Abstract
This document describes a procedure for configuring a host's IPv6
address which prefix is allocated from a DHCPv6 server while it's
interface identifier is independently generated by the host. The
method is applicable to Cryptographically Generated Addresses (CGA).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Address Auto-configuration in SEND . . . . . . . . . . . . . . 4
4. DHCPv6 Operation . . . . . . . . . . . . . . . . . . . . . . . 5
5. DHCPv6 Options . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Identity Association for Prefix Assignment Option . . . . 6
5.2. IA_PD Prefix option . . . . . . . . . . . . . . . . . . . 8
5.3. IA Address Validation Option . . . . . . . . . . . . . . . 8
6. IANA consideration . . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . . 9
9.2. Informative references . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 12
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1. Introduction
[RFC3315] describes the operation of address assignment by a DHCP
server. A client uses a Solicit message to discover DHCP servers
configured to assign addresses. A server sends an Advertise message
in response to announce the availability of the server to the client.
The client then uses a Request message to request addresses. The
server then returns addresses in a Reply message. The operation
assumes that the server is responsible for the assignment of an
integral address which include prefix and interface identifier parts
as described in [RFC4291].
[RFC3633] defines Prefix Delegation options providing a mechanism for
automated delegation of IPv6 prefixes using the DHCPv6. This
mechanism is intended for delegating a long- lived prefix from a
delegating router to a requesting router. The practice of separating
prefix assignment from interface identifier assignment is only used
for routers not hosts.
The following are some scenarios in which separation of prefix and
interface identifier assignment is necessary.
o A DHCP server is incapable of generating an interface identifier
for a host. [RFC3972] describes a method for binding a public
signature key to an IPv6 address in the Secure Neighbor Discovery
(SEND) protocol [RFC3971]. The basic idea is to generate the
interface identifier (i.e., the rightmost 64 bits) of the IPv6
address by computing a cryptographic hash of the public key. That
is, the host decides it's interface identifier.
o A prefix is sufficient to identify a host. [RFC4968] provides
different IPv6 link models that are suitable for 802.16 based
networks and a point-to- point link model is recommended. Also,
3GPP and 3GPP2 have earlier adopted the point-to-point link model
based on the recommendations in [RFC3314]. In this model, one
prefix can only be assigned to one interface of a host (mobile
station) and different hosts (mobile stations) can't share a
prefix. The unique prefix can be used to identify the host. It
is not necessary for a DHCP server to generate an interface
identifier for the host.
A usage of DHCPv6 is proposed in the document to facilitate
separation of prefix and interface identifier assignment. A host's
IPv6 address prefix is allocated from a DHCPv6 server while interface
identifier is independently generated by the host.
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2. Terminology
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 [RFC2119].
The terminology in this document is based on the definitions in
[RFC3315], in addition to the ones specified in this section
Derivative Prefix: A prefix is derived from another prefix. For
example, a /64 prefix is derived from a /48 prefix, that is, the
/64 prefix has the same leftmost 48 bits with the /48 prefix.
Authorized Prefix: A specific router is given a specific set of
subnet prefixes to advertise; other routers have an authorization
to advertise other subnet prefixes. In [RFC3971],Certification
Path Advertisement message is used to convey authorized prefixes.
3. Address Auto-configuration in SEND
Router Advertisements in [RFC4861] allow routers to inform hosts how
to perform Address Auto-configuration. For example, routers can
specify whether hosts should use DHCPv6 and/or stateless address
configuration. In Router Advertisement message, M and O bits are
used for indication of address auto-configuration mode.
Whatever address auto-configuration mode a host uses, the following
two parts are necessary for the host to formulate it's IPv6 address.
o A prefix part. In [RFC3971], Certification Path Solicitation and
Certification Path Advertisement messages are designed for
verifying routers being authorized to act as routers.
Certification Path Advertisement message can also be used to
verify that routers are authorized to advertise a certain set of
subnet prefixes. In stateless auto-configuration mode, the
prefixes in Router Advertisement message should be a subset of
authorized prefixes, or derivative prefixes from authorized
prefixes. In the stateful auto-configuration mode, Section 4
illustrates a procedure for prefix allocation from a DHCPv6
server.
o An interface identifier. The basic idea of [RFC3972] is to
generate the interface identifier (i.e., the rightmost 64 bits) of
the IPv6 address by computing a cryptographic hash of a public key
of a host. The host is responsible for interface identifier
generation.
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4. DHCPv6 Operation
Figure 1 shows the operation of separating prefix assignment and
interface identifier generation using DHCPv6.
+------------+ +-----------+
|Host(Client)| |DHCP Server|
+------------+ +-----------+
| |
| |
| |
| 1 Solicit |
|---------------------> |
| |
| 2 Advertise |
|<--------------------- |
| |
| |
3 Combination of Prefix |
and Interface Identifier |
| |
| |
| 4 Request |
|---------------------> |
| |
| 5 Reply |
|<--------------------- |
| |
| |
Figure 1: DHCPv6 Operation
1. A host uses a Solicit message to discover DHCP servers configured
to assign prefixes for the host. Identity Association for Prefix
Delegation Option (IA_PD) is defined in [RFC3633] for prefix
delegation between a requesting router and delegating router.
Referring to the definition, we design Identity Association for
Prefix Assignment Option (IA-PA) in Section 5.1 for prefix
assignment from a DHCPv6 server to a host. The host uses hints
for prefix assignment preference. In CGA scenario, the hints are
authorized prefixes advertised by an authorized router through
Certification Path Advertisement defined in [RFC3971].
2. Based on the hints, the DHCP server assigns one or more prefixes
to the host. In CGA scenario, the assigned prefixes SHOULD be a
subset of the authorized prefixes or derivative prefixes of the
authorized prefixes. Identity Association for Prefix Assignment
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Option in Section 5.1 is used for conveying the assigned
prefixes. If there is not a proper prefix available, a status-
code is returned to the host and the procedure is terminated.
3. The host generates an interface identifier and formulates a
combined IPv6 address by concatenating the assigned prefix and
the self-generated interface identifier. There are many ways to
generate interface identifier. [RFC3972] defines a method to
generate the interface identifier by computing a cryptographic
hash of a public key of the host. [RFC4941] describes another
way in which interface identifier is derived from IEEE 802
addresses. An interface identifier could even be generated via
random number generation.
4. The host sends a Request message for confirming usage of the
combined address. An IA Address Validation option defined in
Section 5.3 SHOULD be included to convey the combined address.
5. The DHCP server SHOULD verify the uniqueness of the combined IP
address, and send Reply with IA Address Validation option to
grant the usage of the combined address. Otherwise, a status
code is included in the replied IA Address Validation option to
deny the usage of the combined address.
5. DHCPv6 Options
In this section, two new options are defined, Identity Association
for Prefix Assignment Option and IA Address Validation Option. At
the same time, we extend the usage of an existing option, IA_PD
Prefix option.
5.1. Identity Association for Prefix Assignment Option
The IA_PA option is used to carry a prefix assignment identity
association, the parameters associated with the IA_PA and the
prefixes associated with it.
The format of the IA_PA option is:
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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_IA_PA | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IAID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| T2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. IA_PA-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_IA_PA (TDB by IANA)
option-length: 12 + length of IA_PA-options field.
IAID: The unique identifier for this IA_PA; the IAID must
be unique among the identifiers for all of this
host's IA_PAs.
T1: The time at which the host should
contact the DHCPv6 server from which the
prefixes in the IA_PA were obtained to extend the
lifetimes of the prefixes assigned to the IA_PA;
T1 is a time duration relative to the current time
expressed in units of seconds.
T2: The time at which the host should
contact any available DHCPv6 server to extend
the lifetimes of the prefixes assigned to the
IA_PA; T2 is a time duration relative to the
current time expressed in units of seconds.
IA_PA-options: Options associated with this IA_PA.
The details of the fields are similar to the IA_PD option description
in [RFC3633]. The difference is here a DHCP server and a host
involved, while a delegating router and requesting router involved in
[RFC3633].
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5.2. IA_PD Prefix option
IA_PD Prefix option in [RFC3633] is reused here. Originally the
option is used for conveying prefix information between a delegating
router and a requesting router. Here the IA_PD Prefix option is used
to specify IPv6 address prefixes associated with an IA_PA in
Section 5.1. The IA_PD Prefix option must be encapsulated in the
IA_PA-options field of an IA_PA option.
5.3. IA Address Validation Option
The IA Address Validation option must be encapsulated in the Options
field of an IA_NA or IA_TA option. IA_NA and IA_TA are described in
[RFC3315]. A host sends this option to a DHCP server for validating
the usage of an address in the option.
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_IAADDR_VAL | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| preferred-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| valid-lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. IAaddr-options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_IAADDR_VAL(TDB by IANA)
option-len 24 + length of IAaddr-options field.
IPv6 address An IPv6 address.
preferred-lifetime The preferred lifetime for the IPv6 address in
the option, expressed in units of seconds.
valid-lifetime The valid lifetime for the IPv6 address in the
option, expressed in units of seconds.
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IAaddr-options Options associated with this address.
The status of any operations involving this IA Address Validation is
indicated in a Status Code option in the IAaddr-options field. The
details of the fields are the same as the description in [RFC3315].
6. IANA consideration
The value of OPTION_IA_PA and OPTION_IAADDR_VAL should assigned by
IANA.
A status code needs to be assgined by IANA:
ValdidationFailure: a DHCPv6 server can't grant the usage of an
address in IA Address Validation Option
7. Security Considerations
Security considerations in DHCPv6 are described in [RFC3315].
To guard against attacks through prefix assignment and address
confirmation, a host and a DHCPv6 server SHOULD use DHCP
authentication as described in section "Authentication of DHCP
messages" of [RFC3315].
8. Acknowledgements
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
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RFC 3972, March 2005.
[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.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
9.2. Informative references
[RFC4968] Madanapalli, S., "Analysis of IPv6 Link Models for 802.16
Based Networks", RFC 4968, August 2007.
[RFC3314] Wasserman, M., "Recommendations for IPv6 in Third
Generation Partnership Project (3GPP) Standards",
RFC 3314, September 2002.
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Authors' Addresses
Frank Xia
Huawei USA
1700 Alma Dr. Suite 500
Plano, TX 75075
Phone: +1 972-509-5599
Email: xiayangsong@huawei.com
Behcet Sarikaya
Huawei USA
1700 Alma Dr. Suite 500
Plano, TX 75075
Phone: +1 972-509-5599
Email: sarikaya@ieee.org
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