draft-ietf-dhc-dhcpv6-opt-prefix-delegation-00.txt   draft-ietf-dhc-dhcpv6-opt-prefix-delegation-01.txt 
Network Working Group O. Troan DHC Working Group O. Troan
Internet-Draft R. Droms Internet-Draft R. Droms
Expires: April 24, 2003 Cisco Systems Expires: May 28, 2003 Cisco Systems
October 24, 2002 November 27, 2002
IPv6 Prefix Options for DHCPv6 IPv6 Prefix Options for DHCPv6
draft-ietf-dhc-dhcpv6-opt-prefix-delegation-00.txt draft-ietf-dhc-dhcpv6-opt-prefix-delegation-01.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on April 24, 2003. This Internet-Draft will expire on May 28, 2003.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved. Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract Abstract
The Prefix Delegation options provide a mechanism for automated The Prefix Delegation options provide a mechanism for automated
delegation of IPv6 prefixes using DHCP. This prefix delegation delegation of IPv6 prefixes using DHCP. This mechanism is intended
mechanism is intended for simple prefix delegation from a delegating for delegating long-lived prefix from a delegating router to a
router to a requesting router, across an administrative boundary, requesting router, across an administrative boundary, where the
where the delegating router does not require knowledge about the delegating router does not require knowledge about the topology of
topology of the links in the network to which the prefixes will be the links in the network to which the prefixes will be assigned.
assigned.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Model and Applicability . . . . . . . . . . . . . . . . . . 3 4. Model and Applicability . . . . . . . . . . . . . . . . . . 4
5. Overview of DHCP with Prefix Delegation . . . . . . . . . . 6 5. Identity Association for Prefix Delegation . . . . . . . . . 6
6. Identity Association for Prefix Delegation . . . . . . . . . 7 6. Overview of DHCP with Prefix Delegation . . . . . . . . . . 7
7. Interface Selection . . . . . . . . . . . . . . . . . . . . 7 7. Interface Selection . . . . . . . . . . . . . . . . . . . . 7
8. Identity Association for Prefix Delegation Option . . . . . 8 8. Identity Association for Prefix Delegation Option . . . . . 8
9. IA_PD Prefix option . . . . . . . . . . . . . . . . . . . . 9 9. IA_PD Prefix option . . . . . . . . . . . . . . . . . . . . 9
10. Delegating Router Solicitation . . . . . . . . . . . . . . . 11 10. Delegating Router Solicitation . . . . . . . . . . . . . . . 11
10.1 Requesting router behaviour . . . . . . . . . . . . . . . . 11 10.1 Requesting router behaviour . . . . . . . . . . . . . . . . 11
10.2 Delegating router behaviour . . . . . . . . . . . . . . . . 11 10.2 Delegating router behaviour . . . . . . . . . . . . . . . . 12
11. Requesting router initiated prefix delegation . . . . . . . 12 11. Requesting router initiated prefix delegation . . . . . . . 12
11.1 Requesting router behaviour . . . . . . . . . . . . . . . . 12 11.1 Requesting router behaviour . . . . . . . . . . . . . . . . 12
11.2 Delegating Router behaviour . . . . . . . . . . . . . . . . 14 11.2 Delegating Router behaviour . . . . . . . . . . . . . . . . 14
12. Prefix Delegation reconfiguration . . . . . . . . . . . . . 15 12. Prefix Delegation reconfiguration . . . . . . . . . . . . . 15
12.1 Delegating Router behaviour . . . . . . . . . . . . . . . . 15 12.1 Delegating Router behaviour . . . . . . . . . . . . . . . . 15
12.2 Requesting Router behaviour . . . . . . . . . . . . . . . . 15 12.2 Requesting Router behaviour . . . . . . . . . . . . . . . . 15
13. Relay agent behaviour . . . . . . . . . . . . . . . . . . . 15 13. Relay agent behaviour . . . . . . . . . . . . . . . . . . . 15
14. Security Considerations . . . . . . . . . . . . . . . . . . 15 14. Security Considerations . . . . . . . . . . . . . . . . . . 15
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 16 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 16
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 17
Normative References . . . . . . . . . . . . . . . . . . . . 16 Normative References . . . . . . . . . . . . . . . . . . . . 16
Informative References . . . . . . . . . . . . . . . . . . . 17 Informative References . . . . . . . . . . . . . . . . . . . 17
A. Changes from Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 17
draft-troan-dhcpv6-opt-prefix-delegation-01.txt . . . . . . 17
Full Copyright Statement . . . . . . . . . . . . . . . . . . 18 Full Copyright Statement . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
This document describes new options for DHCP, which provide a This document describes new options for DHCP, which provide a
mechanism for the delegation of IPv6 prefixes. Through these mechanism for the delegation of IPv6 prefixes. Through these
options, a delegating router can delegate prefixes to authorised options, a delegating router can delegate prefixes to authorised
requesting routers. requesting routers.
The prefix delegation mechanism described in this document is The prefix delegation mechanism described in this document is
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to requesting routers. It is appropriate for situations in which the to requesting routers. It is appropriate for situations in which the
delegating router does not have knowledge about the topology of the delegating router does not have knowledge about the topology of the
networks to which the requesting router is attached, and the networks to which the requesting router is attached, and the
delegating router does not require other information aside from the delegating router does not require other information aside from the
identity of the requesting router to choose a prefix for delegation. identity of the requesting router to choose a prefix for delegation.
For example, these options would be used by a service provider to For example, these options would be used by a service provider to
assign a prefix to a CPE device acting as a router between the assign a prefix to a CPE device acting as a router between the
subscriber's internal network and the service provider's core subscriber's internal network and the service provider's core
network. network.
Many applications expect stable addresses. Even though this
mechanism makes automatic renumbering easier, it is expected that
prefixes have a long lifespan. During renumbering it is expected
that the old and the new prefix co-exist for some time.
2. Terminology 2. Terminology
This document uses the terminology defined in RFC2460 [2] and the This document uses the terminology defined in RFC2460 [2] and the
DHCP specification [5]. In addition, this document uses the DHCP specification [6]. In addition, this document uses the
following terms: following terms:
requesting router The router that acts as a DHCP client and is requesting router The router that acts as a DHCP client and is
requesting prefix(es) to be assigned. requesting prefix(es) to be assigned.
delegating router The router that acts as a DHCP server, and is delegating router The router that acts as a DHCP server, and is
responding to the prefix request. responding to the prefix request.
Indentity Association for Prefix Delegation (IA_PD) A collection of Identity Association for Prefix Delegation (IA_PD) A collection of
prefixes assigned to the requesting router. Each prefixes assigned to the requesting router. Each
IA_PD has an associated IAID. A requesting IA_PD has an associated IAID. A requesting
router may have more than one IA_PD assigned to router may have more than one IA_PD assigned to
it; for example, one for each of its interfaces. it; for example, one for each of its interfaces.
3. Requirements 3. Requirements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in RFC 2119 [1]. document, are to be interpreted as described in RFC 2119 [1].
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Figure 1: An example of prefix delegation. Figure 1: An example of prefix delegation.
In this example an AAA server is configured with a prefix assigned to In this example an AAA server is configured with a prefix assigned to
the customer at the time of subscription to the ISP service. The the customer at the time of subscription to the ISP service. The
prefix delegation process begins when the requesting router requests prefix delegation process begins when the requesting router requests
configuration information through DHCP. The DHCP messages from the configuration information through DHCP. The DHCP messages from the
requesting router are received by the delegating router in the requesting router are received by the delegating router in the
aggregation device. When the delegating router receives the request, aggregation device. When the delegating router receives the request,
it consults the AAA server to authenticate and authorise the it consults the AAA server to authenticate and authorise the
requesting router. The AAA server returns the subscriber's prefix in requesting router. The AAA server returns the subscriber's
a Framed-IPv6-Prefix attribute as described in RFC 3162 [6], and the prefix(es) in a Framed-IPv6-Prefix attribute as described in RFC 3162
delegating router returns them to the requesting router. [7], and the delegating router returns them to the requesting router.
The requesting router assigns longer prefixes from the delegated The requesting router assigns longer prefixes from the delegated
prefix for assignment to links in the subscriber's network. In a prefix for assignment to links in the subscriber's network. In a
typical scenario based on the network shown in Figure 1, the typical scenario based on the network shown in Figure 1, the
requesting router subnets a single delegated /48 prefix into /64 requesting router subnets a single delegated /48 prefix into /64
prefixes and assigns one /64 prefix to each of the links in the prefixes and assigns one /64 prefix to each of the links in the
subscriber network. subscriber network.
The prefix delegation options can be used in conjunction with other The prefix delegation options can be used in conjunction with other
DHCP options carrying other configuration information to the DHCP options carrying other configuration information to the
requesting router. The requesting router may, in turn, then provide requesting router. The requesting router may, in turn, then provide
DHCP service to hosts attached to the internal network. For example, DHCP service to hosts attached to the internal network. For example,
the requesting router may obtain the addresses of DNS and NTP servers the requesting router may obtain the addresses of DNS and NTP servers
from the ISP delegating router, and then pass that configuration from the ISP delegating router, and then pass that configuration
information on to the subscriber hosts through a DHCP server in the information on to the subscriber hosts through a DHCP server in the
requesting router. requesting router.
5. Overview of DHCP with Prefix Delegation 5. Identity Association for Prefix Delegation
Prefix delegation with DHCP is independent of address assignment and
other configuration information. A requesting router can use DHCP
for just prefix delegation or for prefix delegation along with
address assignment and other configuration information.
A requesting router first creates an IA_PD and assigns it an IAID.
The requesting router then transmits a Solicit message containing an
IA_PD option describing the IA_PD. Delegating routers that can
delegate prefixes to the IA_PD respond to the requesting router with
an Advertise message.
The requesting router may include prefixes in the IA_PDs as a hint to
the delegating router about prefixes for which the requesting router
has a preference.
When the requesting router has identified a delegating router, the
requesting router uses a Request message to populate the IA_PDs with
prefixes. The requesting router includes one or more IA_PD options
in the Request message. The delegating router returns prefixes and
other information about the IA_PDs to the requesting router in IA_PD
options in a Reply message. The requesting router records the
lifetimes for the delegated prefix(es) and uses the prefix(es) as
described in the previous section.
Before the valid lifetime on each delegated prefix expires, the
requesting router includes the prefix in a Prefix Delegation IA
option sent in a Renew message to the delegating router. The
delegating router responds by returning the prefix with updated
lifetimes to the requesting router.
6. Identity Association for Prefix Delegation
An IA_PD is a construct through which a delegating router and a An IA_PD is a construct through which a delegating router and a
requesting router can identify, group and manage a set of related requesting router can identify, group and manage a set of related
IPv6 prefixes. Each IA_PD consists of an IAID and associated IPv6 prefixes. Each IA_PD consists of an IAID and associated
configuration information. A IA_PD for prefixes is the equivalent of configuration information. An IA_PD for prefixes is the equivalent
an IA (described in DHCPv6 specification [5]) for addresses. of an IA (described in DHCPv6 specification [6]) for addresses.
An IA_PD is different from an IA, in that it does not need to be An IA_PD is different from an IA, in that it does not need to be
associated with exactly one interface. One IA_PD can be associated associated with exactly one interface. One IA_PD can be associated
with the requesting router, with a set of interfaces or with exactly with the requesting router, with a set of interfaces or with exactly
one interface. A requesting router must associate at least one one interface. A requesting router must create at least one distinct
distinct IA_PD for the node. It can associate a distinct IA_PD with IA_PD. It may associate a distinct IA_PD with each of its downstream
each of its network interfaces and use that IA_PD to obtain a prefix network interfaces and use that IA_PD to obtain a prefix for that
for that interface from the delegating router. interface from the delegating router.
The IAID uniquely identifies the IA_PD and must be chosen to be The IAID uniquely identifies the IA_PD and must be chosen to be
unique among the IA_PD IDs on the requesting router. The IAID is unique among the IA_PD IDs on the requesting router. The IAID is
chosen by the requesting router. For any given use of an IA_PD by chosen by the requesting router. For any given use of an IA_PD by
the requesting router, the IAID for that IA_PD MUST be consistent the requesting router, the IAID for that IA_PD MUST be consistent
across restarts of the requesting router. The requesting router may across restarts of the requesting router. The requesting router may
maintain consistency either by storing the IAID in non-volatile maintain consistency either by storing the IAID in non-volatile
storage or by using an algorithm that will consistently produce the storage or by using an algorithm that will consistently produce the
same IAID as long as the configuration of the requesting router has same IAID as long as the configuration of the requesting router has
not changed. If the requesting router uses only one IAID, it can use not changed. If the requesting router uses only one IAID, it can use
a well-known value, e.g zero. a well-known value, e.g zero.
The configuration information in an IA_PD consists of one or more The configuration information in an IA_PD consists of one or more
IPv6 prefixes along with the times T1 and T2 for the IA_PD. See IPv6 prefixes along with the times T1 and T2 for the IA_PD. See
section Section 8 for the representation of an IA_PD in a DHCP section Section 8 for the representation of an IA_PD in a DHCP
message. message.
6. Overview of DHCP with Prefix Delegation
Prefix delegation with DHCP is independent of address assignment with
DHCP. A requesting router can use DHCP for just prefix delegation or
for prefix delegation along with address assignment and other
configuration information.
A requesting router first creates an IA_PD and assigns it an IAID.
The requesting router then transmits a Solicit message containing an
IA_PD option describing the IA_PD. Delegating routers that can
delegate prefixes to the IA_PD respond to the requesting router with
an Advertise message.
The requesting router may include prefixes in the IA_PDs as a hint to
the delegating router about specific prefixes for which the
requesting router has a preference.
When the requesting router has identified a delegating router, the
requesting router uses a Request message to populate the IA_PDs with
prefixes. The requesting router includes one or more IA_PD options
in the Request message. The delegating router returns prefixes and
other information about the IA_PDs to the requesting router in IA_PD
options in a Reply message. The requesting router records the
lifetimes for the delegated prefix(es) and uses the prefix(es) as
described in the previous section.
Before the valid lifetime on each delegated prefix expires, the
requesting router includes the prefix in an IA_PD option sent in a
Renew message to the delegating router. The delegating router
responds by returning the prefix with updated lifetimes to the
requesting router.
7. Interface Selection 7. Interface Selection
Delegated prefixes are not associated with a particular interface in Delegated prefixes are not associated with a particular interface in
the same way as addresses are for address assignment, and the rules the same way as addresses are for address assignment, and the rules
described in the section "Client Source Address and Interface described in the section "Client Source Address and Interface
Selection" of the DHCP specification [5] do not apply. Selection" of the DHCP specification [6] do not apply.
When a requesting router sends a DHCP message, it SHOULD be sent on When a requesting router sends a DHCP message, it SHOULD be sent on
the interface associated with the upstream router (ISP network). The the interface associated with the upstream router (ISP network). The
upstream interface is typically determined by configuration. This upstream interface is typically determined by configuration. This
rule applies even in the case where a separate IA_PD is used for each rule applies even in the case where a separate IA_PD is used for each
downstream interface. downstream interface.
When a requesting router sends a DHCP message directly to a When a requesting router sends a DHCP message directly to a
delegating router using unicast (after receiving the Server Unicast delegating router using unicast (after receiving the Server Unicast
option from that delegating router), the source address SHOULD be an option from that delegating router), the source address SHOULD be an
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T2 The time at which the requesting router contacts T2 The time at which the requesting router contacts
any available delegating router to extend the any available delegating router to extend the
lifetimes of the prefixes assigned to the IA_PD; T2 lifetimes of the prefixes assigned to the IA_PD; T2
is a time duration relative to the current time is a time duration relative to the current time
expressed in units of seconds. expressed in units of seconds.
IA_PD-options Options associated with this IA_PD. IA_PD-options Options associated with this IA_PD.
The IA_PD-options field encapsulates those options that are specific The IA_PD-options field encapsulates those options that are specific
to this IA_PD. For example, all of the IA_PD Prefix Options carrying to this IA_PD. For example, all of the IA_PD Prefix Options carrying
the prefixes associated with this IA are in the IA_PD-options field. the prefixes associated with this IA_PD are in the IA_PD-options
field.
An IA_PD option may only appear in the options area of a DHCP An IA_PD option may only appear in the options area of a DHCP
message. A DHCP message may contain multiple IA_PD options. message. A DHCP message may contain multiple IA_PD options.
The status of any operations involving this IA_PD is indicated in a The status of any operations involving this IA_PD is indicated in a
Status Code option in the IA_PD-options field. Status Code option in the IA_PD-options field.
Note that an IA_PD has no explicit "lifetime" or "lease length" of Note that an IA_PD has no explicit "lifetime" or "lease length" of
its own. When the valid lifetimes of all of the prefixes in a IA_PD its own. When the valid lifetimes of all of the prefixes in a IA_PD
have expired, the IA_PD can be considered as having expired. T1 and have expired, the IA_PD can be considered as having expired. T1 and
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IAprefix-options: Options associated with this prefix IAprefix-options: Options associated with this prefix
In a message sent by a requesting router to a delegating router, the In a message sent by a requesting router to a delegating router, the
values in the fields can be used to indicate the requesting router's values in the fields can be used to indicate the requesting router's
preference for those values. The requesting router may send a value preference for those values. The requesting router may send a value
of zero to indicate no preference. A requesting router may set the of zero to indicate no preference. A requesting router may set the
IPv6 prefix field to zero and a given value in the prefix-length IPv6 prefix field to zero and a given value in the prefix-length
field to indicate a preference for the size of the prefix to be field to indicate a preference for the size of the prefix to be
delegated. delegated.
In a message sent by a delegating router the preferred and valid
lifetimes should be set to the values specified in section "Router
Configuration Variables" of RFC2461 [3], unless administratively
configured.
In a message sent by a delegating router to a requesting router, the In a message sent by a delegating router to a requesting router, the
requesting router MUST use the value in the valid lifetime field and requesting router MUST use the value in the valid lifetime field and
MAY use the value for the preferred lifetime. The values in the MAY use the value in the preferred lifetime field. The values in the
preferred and valid lifetimes are the number of seconds remaining in preferred and valid lifetimes are the number of seconds remaining for
each lifetime. each lifetime.
An IA_PD Prefix option may appear only in an IA_PD option. More than An IA_PD Prefix option may appear only in an IA_PD option. More than
one IA_PD Prefix Option can appear in a single IA_PD option. one IA_PD Prefix Option can appear in a single IA_PD option.
The status of any operations involving this IA_PD Prefix option is The status of any operations involving this IA_PD Prefix option is
indicated in a Status Code option in the IAprefix-options field. indicated in a Status Code option in the IAprefix-options field.
10. Delegating Router Solicitation 10. Delegating Router Solicitation
The requesting router locates and selects a delegating router in the The requesting router locates and selects a delegating router in the
same way as described in section "DHCP Server Solicitation" of the same way as described in section "DHCP Server Solicitation" of the
DHCP specification [5]. The details of the solicitation process are DHCP specification [6]. The details of the solicitation process are
described in this section. described in this section.
10.1 Requesting router behaviour 10.1 Requesting router behaviour
The requesting router creates and transmits a Solicit message as The requesting router creates and transmits a Solicit message as
described in sections "Creation of Solicit Messages" and described in sections "Creation of Solicit Messages" and
"Transmission of Solicit Messages" of the DHCP specification [5]. "Transmission of Solicit Messages" of the DHCP specification [6].
The requesting router creates an IA_PD and assigns it an IAID. The The requesting router creates an IA_PD and assigns it an IAID. The
requesting router MUST include the IA_PD option in the Solicit requesting router MUST include the IA_PD option in the Solicit
message. message.
The requesting router processes any received Advertise messages as The requesting router processes any received Advertise messages as
described in section "Receipt of Advertise Messages" in the DHCP described in section "Receipt of Advertise Messages" in the DHCP
specification [5]. The requesting router MAY choose to consider the specification [6]. The requesting router MAY choose to consider the
presence of advertised prefixes in its decision about which presence of advertised prefixes in its decision about which
delegating router to respond to. delegating router to respond to.
The requesting router MUST ignore any Advertise message that includes The requesting router MUST ignore any Advertise message that includes
a Status Code option containing the value NoPrefixAvail, with the a Status Code option containing the value NoPrefixAvail, with the
exception that the requesting router MAY display the associated exception that the requesting router MAY display the associated
status message to the user. status message to the user.
10.2 Delegating router behaviour 10.2 Delegating router behaviour
The delegating router processes Solicit messages from requesting The delegating router processes Solicit messages from requesting
routers in the same way as described in section "Receipt of Solicit routers in the same way as described in section "Receipt of Solicit
messages" of the DHCP specification [5]. If the message contains an messages" of the DHCP specification [6]. If the message contains an
IA_PD option and the delegating router is configured to delegate IA_PD option and the delegating router is configured to delegate
prefix(es) to the requesting router, the delegating router selects prefix(es) to the requesting router, the delegating router selects
the prefix(es) to be delegated to the requesting router. The the prefix(es) to be delegated to the requesting router. The
mechanism through which the delegating router selects prefix(es) for mechanism through which the delegating router selects prefix(es) for
delegation is not specified in this document. Examples of ways in delegation is not specified in this document. Examples of ways in
which the delegating router might select prefix(es) for a requesting which the delegating router might select prefix(es) for a requesting
router include: static assignment based on subscription to an ISP; router include: static assignment based on subscription to an ISP;
dynamic assignment from a pool of available prefixes; selection based dynamic assignment from a pool of available prefixes; selection based
on an external authority such as a RADIUS server using the Framed- on an external authority such as a RADIUS server using the Framed-
IPv6-Prefix option as described in RFC 3162 [6]. IPv6-Prefix option as described in RFC 3162 [7].
If the requesting router includes an IA_PD Prefix option in the IA_PD If the requesting router includes an IA_PD Prefix option in the IA_PD
option in its Solicit message, the delegating router MAY choose to option in its Solicit message, the delegating router MAY choose to
use the information in that option to select the prefix(es) or prefix use the information in that option to select the prefix(es) or prefix
size to be delegated to the requesting router. size to be delegated to the requesting router.
The delegating router sends an Advertise message to the requesting The delegating router sends an Advertise message to the requesting
router in the same way as described in section "Creation and router in the same way as described in section "Creation and
transmission of Advertise messages" in the DHCP specification [5]. transmission of Advertise messages" in the DHCP specification [6].
The delegating router MUST include an IA_PD option, identifying any The delegating router MUST include an IA_PD option, identifying any
prefix(es) that the delegating router will delegate to the requesting prefix(es) that the delegating router will delegate to the requesting
router. router.
If the delegating router will not assign any prefixes to any IA_PDs If the delegating router will not assign any prefixes to any IA_PDs
in a subsequent Request from the requesting router, the delegating in a subsequent Request from the requesting router, the delegating
router MUST send an Advertise message to the requesting router that router MUST send an Advertise message to the requesting router that
includes a Status Code option with code NoPrefixAvail and a status includes a Status Code option with code NoPrefixAvail and a status
message for the user, a Server Identifier option with the delegating message for the user, a Server Identifier option with the delegating
router's DUID and a Client Identifier option with the requesting router's DUID and a Client Identifier option with the requesting
router's DUID. router's DUID.
11. Requesting router initiated prefix delegation 11. Requesting router initiated prefix delegation
A requesting router uses the same message exchanges as described in A requesting router uses the same message exchanges as described in
section "DHCP Client-Initiated Configuration Exchange" of the DHCP section "DHCP Client-Initiated Configuration Exchange" of the DHCP
specification [5] to obtain or update prefix(es) from a delegating specification [6] to obtain or update prefix(es) from a delegating
router. The requesting router and the delegating router use the router. The requesting router and the delegating router use the
IA_PD option to exchange information about prefix(es) in much the IA_PD Prefix option to exchange information about prefix(es) in much
same way IA Address options are used for assigned addresses. the same way IA Address options are used for assigned addresses.
11.1 Requesting router behaviour 11.1 Requesting router behaviour
The requesting router uses a Request message to populate IA_PDs with The requesting router uses a Request message to populate IA_PDs with
prefixes. The requesting router includes one or more IA_PD options prefixes. The requesting router includes one or more IA_PD options
in the Request message. The delegating router then returns the in the Request message. The delegating router then returns the
prefixes about the IA_PDs to the requesting router in IA_PD options prefixes for the IA_PDs to the requesting router in IA_PD options in
in a Reply message. a Reply message.
The requesting router includes IA_PD options in any Renew, or Rebind The requesting router includes IA_PD options in any Renew, or Rebind
messages sent by the requesting router. The IA_PD option include all messages sent by the requesting router. The IA_PD option include all
of the prefixes the requesting router currently has associated with of the prefixes the requesting router currently has associated with
that IA_PD. that IA_PD.
In some circumstances the requesting router may need verification In some circumstances the requesting router may need verification
that the delegating router still has a valid binding for the that the delegating router still has a valid binding for the
requesting router. Examples of times when a requesting router may requesting router. Examples of times when a requesting router may
ask for such verification include: ask for such verification include:
o The requesting router reboots. o The requesting router reboots.
o The requesting router's upstream link flaps. o The requesting router's upstream link flaps.
o The requesting router is physically disconnected from a wired o The requesting router is physically disconnected from a wired
connection. connection.
If such verification is needed the requesting router MUST initiate a If such verification is needed the requesting router MUST initiate a
Renew/Reply message exchange as described in the section "Creation Renew/Reply message exchange as described in the section "Creation
and Transmission of Renew Messages" of the DHCP specification [5]. and Transmission of Renew Messages" of the DHCP specification [6].
The requesting router includes any IA_PDs, along with prefixes The requesting router includes any IA_PDs, along with prefixes
associated with those IA_PDs in its Renew message. associated with those IA_PDs in its Renew message.
Each prefix has valid and preferred lifetimes whose duration is Each prefix has valid and preferred lifetimes whose duration is
specified in the IA_PD Prefix option for that prefix. The requesting specified in the IA_PD Prefix option for that prefix. The requesting
router uses Renew and Rebind messages to request the extension of the router uses Renew and Rebind messages to request the extension of the
lifetimes of a delegated prefix. lifetimes of a delegated prefix.
The requesting router uses a Release message to return a delegated The requesting router uses a Release message to return a delegated
prefix to a delegating router. The prefixes to be released MUST be prefix to a delegating router. The prefixes to be released MUST be
included in the IA_PDs. included in the IA_PDs.
The Confirm and Decline messages are not used with Prefix Delegation. The Confirm and Decline message types are not used with Prefix
Delegation.
Upon the receipt of a valid Reply message, the requesting router Upon the receipt of a valid Reply message, the requesting router
assigns a subnet from each of the delegated prefixes to each of the assigns a subnet from each of the delegated prefixes to each of the
links to which it is attached, with the following exception: the links to which it is attached, with the following exception: the
requesting router MUST NOT assign any delegated prefixes or subnets requesting router MUST NOT assign any delegated prefixes or subnets
from the delegated prefix(es) to the link through which it received from the delegated prefix(es) to the link through which it received
the DHCP message from the delegating router. the DHCP message from the delegating router.
When a requesting router subnets a delegated prefix, it must assign When a requesting router subnets a delegated prefix, it must assign
additional bits to the prefix to generate unique, longer prefixes. additional bits to the prefix to generate unique, longer prefixes.
skipping to change at page 14, line 21 skipping to change at page 14, line 27
the valid lifetime specified in the IA_PD Prefix option. A the valid lifetime specified in the IA_PD Prefix option. A
requesting router MAY use the preferred lifetime specified in the requesting router MAY use the preferred lifetime specified in the
IA_PD Prefix option. IA_PD Prefix option.
11.2 Delegating Router behaviour 11.2 Delegating Router behaviour
When a delegating router receives a Request message from a requesting When a delegating router receives a Request message from a requesting
router that contains an IA_PD option, and the delegating router is router that contains an IA_PD option, and the delegating router is
authorised to delegate prefix(es) to the requesting router, the authorised to delegate prefix(es) to the requesting router, the
delegating router selects the prefix(es) to be delegated to the delegating router selects the prefix(es) to be delegated to the
requesting router. If the requesting router includes an IA_PD Prefix requesting router. The mechanism through which the delegating router
option in its Solicit message, the delegating router MAY choose to selects prefix(es) for delegation is not specified in this document.
use the information in that option to select the prefix(es) to be Section 10.2 gives examples of ways in which a delegating router
delegated to the requesting router. The mechanism through which the might select the prefix(es) to be delegated to a requesting router.
delegating router selects prefix(es) for delegation is not specified
in this document. Section 10.2 gives examples of ways in which a
delegating router might select the prefix(es) to be delegated to a
requesting router.
A delegating router examines the prefix(es) identified in IA_PD A delegating router examines the prefix(es) identified in IA_PD
Prefix options (in an IA_PD option) in Renew and Rebind messages and Prefix options (in an IA_PD option) in Renew and Rebind messages and
responds according to the current status of the prefix(es). The responds according to the current status of the prefix(es). The
delegating router returns IA_PD Prefix options (within an IA_PD delegating router returns IA_PD Prefix options (within an IA_PD
option) with updated lifetimes for each valid prefix in the message option) with updated lifetimes for each valid prefix in the message
from the requesting router. If the delegating router cannot find a from the requesting router. If the delegating router cannot find a
binding for the requesting router's IA_D the delegating router binding for the requesting router's IA_PD the delegating router
returns the IA_PD containing no prefixes with a Status Code option returns the IA_PD containing no prefixes with a Status Code option
set to NoBinding in the Reply message. If the delegating router set to NoBinding in the Reply message. If the delegating router
finds that any of the prefixes are not in the requesting router's finds that any of the prefixes are not in the requesting router's
binding entry, the delegating router returns the prefix to the binding entry, the delegating router returns the prefix to the
requesting router with lifetimes of 0. requesting router with lifetimes of 0.
A delegating router may mark any prefix(es) in IA_PD Prefix options A delegating router may mark any prefix(es) in IA_PD Prefix options
in a Release message from a requesting router as "available", in a Release message from a requesting router as "available",
dependent on the mechanism used to acquire the prefix, e.g in the dependent on the mechanism used to acquire the prefix, e.g in the
case of a dynamic pool. case of a dynamic pool.
skipping to change at page 15, line 14 skipping to change at page 15, line 14
12. Prefix Delegation reconfiguration 12. Prefix Delegation reconfiguration
This section describes prefix delegation in Reconfigure message This section describes prefix delegation in Reconfigure message
exchanges. exchanges.
12.1 Delegating Router behaviour 12.1 Delegating Router behaviour
The delegating router initiates a configuration message exchange with The delegating router initiates a configuration message exchange with
a requesting router, as described in the section "DHCP Server- a requesting router, as described in the section "DHCP Server-
Initiated Configuration Exchange" of the DHCP specification [5]. The Initiated Configuration Exchange" of the DHCP specification [6]. The
delegating router specifies the IA_PD option in the Option Request delegating router specifies the IA_PD option in the Option Request
option to cause the requesting router to include a IA_PD option to option to cause the requesting router to include an IA_PD option to
obtain new information about delegated prefix(es). obtain new information about delegated prefix(es).
12.2 Requesting Router behaviour 12.2 Requesting Router behaviour
The requesting router responds to a Reconfigure message received from The requesting router responds to a Reconfigure message received from
a delegating router as described in the DHCP specification [5]. The a delegating router as described in the DHCP specification [6]. The
requesting router MUST include the IA_PD Prefix option(s) (in a IA_PD requesting router MUST include the IA_PD Prefix option(s) (in an
option) for prefix(es) that have been delegated to the requesting IA_PD option) for prefix(es) that have been delegated to the
router by the delegating router from which the Reconfigure message requesting router by the delegating router from which the Reconfigure
was received. message was received.
13. Relay agent behaviour 13. Relay agent behaviour
A relay agent forwards messages containing Prefix Delegation options A relay agent forwards messages containing Prefix Delegation options
in the same way as described in section "Relay Behaviour" of the DHCP in the same way as described in section "Relay Behaviour" of the DHCP
specification [5]. specification [6].
If a delegating router communicates with a requesting router through If a delegating router communicates with a requesting router through
a relay agent, the delegating router may need a protocol or other a relay agent, the delegating router may need a protocol or other
out-of-band communication to add routing information for delegated out-of-band communication to add routing information for delegated
prefixes into the provider edge router. prefixes into the provider edge router.
14. Security Considerations 14. Security Considerations
Security considerations in DHCP are described in the section Security considerations in DHCP are described in the section
"Security Considerations" of the DHCP specification [5]. "Security Considerations" of the DHCP specification [6].
A rogue delegating router can issue bogus prefixes to a requesting A rogue delegating router can issue bogus prefixes to a requesting
router. This may cause denial of service due to unreachability. router. This may cause denial of service due to unreachability.
An intruder requesting router may be able to mount a denial of An intruder requesting router may be able to mount a denial of
service attack by repeated requests for delegated prefixes that service attack by repeated requests for delegated prefixes that
exhaust the delegating router's available prefixes. exhaust the delegating router's available prefixes.
To guard against attacks through prefix delegation, requesting To guard against attacks through prefix delegation, requesting
routers and delegating routers SHOULD use DHCP authentication as routers and delegating routers SHOULD use DHCP authentication as
described in section "Authentication of DHCP messages" in the DHCP described in section "Authentication of DHCP messages" in the DHCP
specification [5]. For point to point links, where one trusts that specification [6]. For point to point links, where one trusts that
there is no man in the middle, or one trusts layer two there is no man in the middle, or one trusts layer two
authentication, DHCP authentication or IPsec is not necessary. authentication, DHCP authentication or IPsec may not be necessary.
Because a requesting router and delegating routers must each have at Because a requesting router and delegating routers must each have at
least one assigned IPv6 address, the routers may be able to use IPsec least one assigned IPv6 address, the routers may be able to use IPsec
for authentication of DHCPv6 messages. The details of using IPsec for authentication of DHCPv6 messages. The details of using IPsec
for DHCPv6 are under development. for DHCPv6 are under development.
15. IANA Considerations 15. IANA Considerations
IANA is requested to assign option codes to these options from the IANA is requested to assign option codes to these options from the
option-code space as defined in section "DHCPv6 Options" of the option-code space as defined in section "DHCPv6 Options" of the
DHCPv6 specification [5]. DHCPv6 specification [6].
IANA is requested to assign a status code to the NoPrefixAvail status IANA is requested to assign a status code to the NoPrefixAvail status
code from the status-code space as defined in section "Status Codes" code from the status-code space as defined in section "Status Codes"
of the DHCPv6 specification [5]. of the DHCPv6 specification [6].
16. Acknowledgements 16. Acknowledgements
Thanks for the input and review by (in alphabetical order) Steve Thanks for the input and review by (in alphabetical order) Steve
Deering, Dave Forster, Brian Haberman, Tatuya Jinmei, Shin Miyakawa, Deering, Dave Forster, Brian Haberman, Tatuya Jinmei, Shin Miyakawa,
Pekka Savola, Bernie Volz and Toshi Yamasaki. Pekka Savola, Bernie Volz, Trevor Warwick and Toshi Yamasaki.
Normative References Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998. Specification", RFC 2460, December 1998.
[3] Hinden, R. and S. Deering, "IP Version 6 Addressing [3] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
IP Version 6 (IPv6)", RFC 2461, December 1998.
[4] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998. Architecture", RFC 2373, July 1998.
[4] Thomson, S. and T. Narten, "IPv6 Stateless Address [5] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998. Autoconfiguration", RFC 2462, December 1998.
[5] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R. [6] Bound, J., Carney, M., Perkins, C., Lemon, T., Volz, B. and R.
Droms (ed.), "Dynamic Host Configuration Protocol for IPv6 Droms (ed.), "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", draft-ietf-dhc-dhcpv6-27 (work in progress), (DHCPv6)", draft-ietf-dhc-dhcpv6-27 (work in progress),
September 2002. September 2002.
[6] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC 3162, [7] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC 3162,
August 2001. August 2001.
Informative References Informative References
[7] Miyakawa, S., "Requirements for IPv6 prefix delegation", draft-
miyakawa-ipv6-prefix-delegation-requirement-00 (work in [8] Miyakawa, S., "Requirements for IPv6 prefix delegation", draft-
progress), June 2002. ietf-ipv6-prefix-delegation-requirement-00 (work in progress),
November 2002.
Authors' Addresses Authors' Addresses
Ole Troan Ole Troan
Cisco Systems Cisco Systems
4 The Square 4 The Square
Stockley Park Stockley Park
Uxbridge UB11 1BL Uxbridge UB11 1BL
United Kingdom United Kingdom
skipping to change at page 17, line 28 skipping to change at page 18, line 4
EMail: ot@cisco.com EMail: ot@cisco.com
Ralph Droms Ralph Droms
Cisco Systems Cisco Systems
300 Apollo Drive 300 Apollo Drive
Chelmsford, MA 01824 Chelmsford, MA 01824
USA USA
Phone: +1 978 497 4733 Phone: +1 978 497 4733
EMail: rdroms@cisco.com EMail: rdroms@cisco.com
Appendix A. Changes from draft-troan-dhcpv6-opt-prefix-delegation-01.txt
o The IA_PD option is now consistent with the IA options. Most IA-
isms have been adopted from the base specification. That includes
adding the identifier and T1/T2 fields to the IA_PD option.
o Replaced lease duration with preferred/valid lifetime to improve
renumbering support.
o Removed the Prefix Request option. The requesting router can
indicate its preference for various prefix parameters using the
IA_PD Prefix option, therefore the Prefix Request option is not
needed.
o Added a new status code NoPrefixAvail.
o Updated to be in line with draft-ietf-dhc-dhcpv6-27.txt
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved. Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
 End of changes. 

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