Internet DRAFT - draft-ietf-dhc-host-gen-id
draft-ietf-dhc-host-gen-id
Network Working Group S. Jiang, Ed.
Internet-Draft F. Xia
Intended status: Standards Track B. Sarikaya
Expires: August 29, 2013 Huawei Technologies
February 25, 2013
Prefix Assignment in DHCPv6
draft-ietf-dhc-host-gen-id-05
Abstract
This document introduces a generic host-oriented prefix assignment
mechanism using DHCPv6. In this new address configuration procedure,
the prefix is assigned from a DHCPv6 server to hosts through DHCPv6
message exchanging while the interface identifiers are independently
generated by the hosts. It enables both integral address assignment
and self-generated addresses in one single mechanism, DHCPv6. It
also enables stateless address configuration without RA attendance.
The technique described in this document can be used in networks
which assign IPv6 addresses using DHCPv6, e.g. WiMAX.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 29, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Address Auto-configuration . . . . . . . . . . . . . . . . . . 5
5. DHCPv6 Operation . . . . . . . . . . . . . . . . . . . . . . . 5
6. DHCPv6 IA_PA Option . . . . . . . . . . . . . . . . . . . . . 7
6.1. Identity Association for Prefix Assignment Option . . . . 7
6.2. IA_PA Prefix Option . . . . . . . . . . . . . . . . . . . 9
7. IANA consideration . . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . . 9
10.2. Informative references . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
A host IPv6 address is combined by a prefix and an interface
identifier. Currently, there are two mechanisms to configure a host
IPv6 address. [RFC3315] describes the operation of address
assignment by a DHCPv6 server. The operation assumes that the server
is responsible for the assignment of an integral address which
includes both prefix and interface identifier parts as described in
[RFC4291]. In the Stateless Address Autoconfiguration (SLACC,
[RFC4862]) model, the interface Identifier is generated by the host
itself while the prefix is configured through Router Advertisement
message defined in [RFC4861].
However, in a DHCPv6-managed network, assigning 128-bit address is
insufficient. Some hosts may want to use self-generated address,
which are combined by prefixes obtained from network configuration
and interface identifiers generated by hosts. The applicable user
cases include CGA [RFC3972], modified EUI-64 interface identifier
[EUI-64], temporary addresses for privacy [RFC4941] and etc.
In these scenarios, the address configuration precedure has to be
splitted in two motheds: integral address assignment through DHCPv6
and prefix announcement by RA advertisement. Some ISPs desire to
manage address configuration using one set of protocol, rather than
mixture of DHCPv6 and Neighbor Discovery.
There are also some network environments in that perfix annoucement
through RAs may not be the best choice. For example, hosts may
connect through tunnels, either layer 2 tunnels or layer 3 tunnels.
While a RA is only able to announce prefix on a single link, DHCPv6
configuration can be used to manage multiple links by setup DHCPv6
relay.
Up to now, there is no mechanism for host-oriented prefix assignment
in DHCPv6. [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. This mechanism "is not
bound to the assignment of IP addresses or other configuration
information to hosts" [RFC3633]. It delegates prefixes to a routable
device for itself use only. It does not support the host-generated
interface identifiers model, in which prefix(es) need to be
propagated to hosts.
This document introduces a generic prefix assignment mechanism using
DHCPv6. In this new address configuration procedure, the prefix is
propagated from a DHCPv6 server to hosts through DHCPv6 message
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exchanging while the interface identifiers are independently
generated by the hosts. It enables both integral address assignment
and self-generated addresses in one single mechanism, DHCPv6. Note,
in many scenarios, Neighbor Discovery [RFC4861] is still needed for
routing and reachability. In other scenarios, this mechanism enables
stateless address configuration while RA absents.
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 mainly based on the definitions
in [RFC3315] and [RFC3633].
Prefix assignment: a DHCPv6 server propagates prefix information to
hosts in unicast model.
3. Applicability
In point-to-point link model, DHCPv6 operation with host-generated
interface identifier, described in this document, may be used.
[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 DHCPv6 server to generate an interface identifier for
the host. The host may generate its interface identifier as
described in [RFC4941]. An interface identifier could even be
generated via random number generation.
[RFC3972] defines Cryptographically Generated Addresses (CGA), which
is generated from a giving prefix and a public signature key. For
security reasons, it is only proper to be generated the user, the
host itself. It requests a prefix before the interface identifier
can be computed.
Modified EUI-64 interface identifier [EUI-64] is also typically
generated by hosts. [RFC4941] has defined temporary addresses for
privacy purposes. The temporary addresses is also generated by hosts
using random algorithm.
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The DHCPv6 operations defined in this document supports
abovementioned address methods, and the host-generated addresses that
may defined in the future.
4. Address Auto-configuration
Router Advertisements in ND [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. "A bit string that consists of some number of initial
bits of an address" [RFC4861]. The prefixes can be announced
through Router Advertisement message. Prefix assignment from a
DHCPv6 server is not currently support.
o An interface identifier. "From address autoconfiguration's
perspective, an interface identifier is a bit string of known
length" [RFC4862]. Modified EUI-64 interface identifier [EUI-64]
is a widely-used host generated interface identifier. It
generates interface identifier from the host MAC address. The
interface identifier of CGA [RFC3972] is generated by computing a
preifx that will be used to form the CGA and a cryptographic hash
of a public key of a host. The host is responsible for interface
identifier generation.
In the ND-managed environment, RA is used to assign the prefix.
So far, there is no mechanism to support the scenario that prefixes
are managed by a DHCPv6 server. This document targets to meet this
gap. The DHCPv6 operation defined in this document enables the
DHCPv6 server to assign a prefix, rather than a integral address, to
the host, so that the host can obtain an IPv6 address by combining
the prefix with its own generated interface identifier. It enables
the auto address configuration through DHCPv6.
5. DHCPv6 Operation
Figure 1 shows the operation of separating prefix assignment and
interface identifier generation in the DHCPv6.
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+------------+ +-------------+
|Host(Client)| |DHCPv6 Server|
+------------+ +-------------+
| 1 Solicit/Request |
|---------------------> |
| 2 Reply with IA_PA |
|<--------------------- |
3 Combination of Prefix |
and Interface Identifier |
| |
Figure 1: DHCPv6 Operation
1. A host uses a Solicit message to discover DHCPv6 servers.
Indications of information requests can be included in the
Solicit message or a Request message after discovery procedure.
If a host that wants to use host generated addresses, it SHOULD
request prefix assignment explicitly by including an IA_PA in a
Solicit or a Request message, in which an IAID is provided by the
host.
2. The DHCPv6 server assigns one or more prefixes to the host in the
Reply messages responding to the prefix requests from the hosts.
A server MUST return the same set of prefixes for the same IA_PA
(as identified by the IAID) as long as those prefixes are still
valid. After the lifetimes of the prefixes in an IA_TA have
expired, the IAID may be reused to identify a new IA_PA with new
prefix. If there is not a proper prefix available, a
NoPrefixAvail (defined in [RFC3633]) 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.
After the host generates an IPv6 address using the above procedure,
the host may send a Request message to the DHCPv6 server in order to
confirm the usage of the new address. The confirmation procedure may
be completed together with the address registration procedure
[I-D.ietf-dhc-addr-registration]. However, the confirmation
procedure is out of scope.
When the host reaches T1 or T2 defined in Section 6.1, it SHOULD use
the same message exchanges, as described in section 18, "DHCP Client-
Initiated Configuration Exchange" of [RFC3315], to obtain or update
prefix(es) from a DHCPv6 server.
A DHCPv6 server MAY initiatively send a reconfiguration message to
the host, as described in section 19, "DHCP Server-Initiated
Configuration Exchange" of [RFC3315], to cause prefix(es) information
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update.
If an IA_PA capable client connects to a network, and the DHCPv6
server is not IA_PA capable, the Solicit or Request message with
IA_PA Option will result in no Reply, Reply without IA_PAs, or Reply
with a Status Code containing UnspecFail. The client MAY decide the
network does not support IA_PA immediately or after a period of
soliciting (with limited retransmissions times). Then, it MAY
"failover" to IA_NA/IA_TA requests.
6. DHCPv6 IA_PA Option
In this section, one new option is defined, Identity Association for
Prefix Assignment Option . The format of this new DHCPv6 IA_PA
Option has been deliberately designed to be the same with IA_PD
option[RFC3633]. The IA_PD Prefix and IA Address sub-options from
IA_PD option are also reused. However, the two options are different
on the semantics and usage models.
Comparing with Prefix Information Option in ND, Section 4.6.2 of
[RFC4861], the IA_PA option does not provide L flag and A flag. The
A (autonomous address-configuration flag) isn't need obviously
because the IA_PA is implicit for stateless address configuration.
Because the IA_PA is only address relevant, it does not relevant to
reachability or routing and the DHCPv6 server may not sure the on-
link state. So L (on-Link) flag is not include. The DHCPv6 client
should treat the prefix as same as L flag not set, which makes no
statement about on-link or off-link properties of the prefix.
6.1. 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 (TBA1)
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. The number space for IA_PA IAIDs is
separate from the number spaces for IA_TA and IA_NA
IAIDs
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 DHCPv6 server and a host
involved, while a delegating router and requesting router involved in
[RFC3633].
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6.2. IA_PA Prefix Option
OPTION_IAPREFIX (26) "IA_PD Prefix Option" defined in Section 10 of
[RFC3633] is reused.
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 6.1. The IA_PD Prefix option must be
encapsulated in the IA_PA-options field of an IA_PA option.
Note, the PD_EXCLUDE option [RFC6603] SHOULD NOT be encapsulated in
the IAPREFIX options that are encapsulated in an IA_PA.
7. IANA consideration
This document defines a new DHCPv6 [RFC3315] option, which must be
assigned Option Type values within the option numbering space for
DHCPv6 messages:
The OPTION_IA_PA Option (TBA1), described in Section 6.1.
8. Security Considerations
Security considerations in DHCPv6 are described in [RFC3315].
To guard against attacks through prefix assignment, a host and a
DHCPv6 server SHOULD use DHCPv6 authentication as described in
Section 21, "Authentication of DHCP messages" of [RFC3315] or Secure
DHCPv6 [I-D.ietf-dhc-secure-dhcpv6] .
9. Acknowledgements
The authors would like to thanks Suresh Krishnan, Ted Lemon, Bing
Liu, Andre Kostur, Gaurav Halwasia, Bernie Volz and other members of
DHC WG for their valuable comments.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[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.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC6603] Korhonen, J., Savolainen, T., Krishnan, S., and O. Troan,
"Prefix Exclude Option for DHCPv6-based Prefix
Delegation", RFC 6603, May 2012.
10.2. Informative references
[RFC3314] Wasserman, M., "Recommendations for IPv6 in Third
Generation Partnership Project (3GPP) Standards",
RFC 3314, September 2002.
[RFC4968] Madanapalli, S., "Analysis of IPv6 Link Models for 802.16
Based Networks", RFC 4968, August 2007.
[I-D.ietf-dhc-secure-dhcpv6]
Jiang, S. and S. Shen, "Secure DHCPv6 Using CGAs",
draft-ietf-dhc-secure-dhcpv6-07 (work in progress),
September 2012.
[I-D.ietf-dhc-addr-registration]
Jiang, S., Chen, G., and S. Krishnan, "A Generic IPv6
Addresses Registration Solution Using DHCPv6",
draft-ietf-dhc-addr-registration-01 (work in progress),
October 2012.
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[EUI-64] "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority", http://standards.ieee.org/
regauth/oui/tutorials/EUI64.html", March 1997.
Authors' Addresses
Sheng Jiang (editor)
Huawei Technologies
Q14, Huawei Campus, No.156, BeiQing Road
Hai-Dian District, Beijing 100095
P.R. China
Email: jiangsheng@huawei.com
Frank Xia
Huawei Technologies
1700 Alma Dr. Suite 500
Plano, TX 75075
Email: xiayangsong@huawei.com
Behcet Sarikaya
Huawei Technologies
1700 Alma Dr. Suite 500
Plano, TX 75075
Email: sarikaya@ieee.org
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