draft-ietf-dhc-dhcpv6-opt-prefix-delegation-04.txt   draft-ietf-dhc-dhcpv6-opt-prefix-delegation-05.txt 
Network Working Group O. Troan DHC Working Group O. Troan
Internet-Draft R. Droms Internet-Draft R. Droms
Expires: December 5, 2003 Cisco Systems Expires: April 6, 2004 Cisco Systems
June 6, 2003 October 7, 2003
IPv6 Prefix Options for DHCPv6 IPv6 Prefix Options for DHCPv6
draft-ietf-dhc-dhcpv6-opt-prefix-delegation-04.txt draft-ietf-dhc-dhcpv6-opt-prefix-delegation-05.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.
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This Internet-Draft will expire on December 5, 2003. This Internet-Draft will expire on April 6, 2004.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2003). 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 mechanism is intended delegation of IPv6 prefixes using DHCP. This mechanism is intended
for delegating a long-lived prefix from a delegating router to a for delegating a long-lived prefix from a delegating router to a
skipping to change at page 2, line 29 skipping to change at page 2, line 29
11.1 Requesting router behaviour . . . . . . . . . . . . . . . . 11 11.1 Requesting router behaviour . . . . . . . . . . . . . . . . 11
11.2 Delegating router behaviour . . . . . . . . . . . . . . . . 12 11.2 Delegating router behaviour . . . . . . . . . . . . . . . . 12
12. Requesting router initiated prefix delegation . . . . . . . 12 12. Requesting router initiated prefix delegation . . . . . . . 12
12.1 Requesting router behaviour . . . . . . . . . . . . . . . . 13 12.1 Requesting router behaviour . . . . . . . . . . . . . . . . 13
12.2 Delegating Router behaviour . . . . . . . . . . . . . . . . 14 12.2 Delegating Router behaviour . . . . . . . . . . . . . . . . 14
13. Prefix Delegation reconfiguration . . . . . . . . . . . . . 15 13. Prefix Delegation reconfiguration . . . . . . . . . . . . . 15
13.1 Delegating Router behaviour . . . . . . . . . . . . . . . . 15 13.1 Delegating Router behaviour . . . . . . . . . . . . . . . . 15
13.2 Requesting Router behaviour . . . . . . . . . . . . . . . . 16 13.2 Requesting Router behaviour . . . . . . . . . . . . . . . . 16
14. Relay agent behaviour . . . . . . . . . . . . . . . . . . . 16 14. Relay agent behaviour . . . . . . . . . . . . . . . . . . . 16
15. Security Considerations . . . . . . . . . . . . . . . . . . 16 15. Security Considerations . . . . . . . . . . . . . . . . . . 16
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . 16 16. IANA Considerations . . . . . . . . . . . . . . . . . . . . 17
17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17 17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
18. Changes in draft-ietf-dhc-dhcpv6-opt-prefix-delegation-03 . 17 Normative References . . . . . . . . . . . . . . . . . . . . 17
References . . . . . . . . . . . . . . . . . . . . . . . . . 17 Informative References . . . . . . . . . . . . . . . . . . . 18
References . . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 18
Full Copyright Statement . . . . . . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . 19
1. Introduction 1. Introduction
This document describes new options for DHCP that provide a mechanism This document describes new options for DHCP that provide a mechanism
for the delegation of IPv6 prefixes. Through these options, a for the delegation of IPv6 prefixes [1]. Through these options, a
delegating router can delegate prefixes to authorised requesting delegating router can delegate prefixes to authorised requesting
routers. routers.
The prefix delegation mechanism described in this document is The prefix delegation mechanism described in this document is
intended for simple delegation of prefixes from a delegating router intended for simple delegation of prefixes from a delegating router
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 Many applications expect stable addresses. Even though this mechanism
mechanism makes automatic renumbering easier, it is expected that makes automatic renumbering easier, it is expected that prefixes have
prefixes have a long lifespan. During renumbering it is expected a long lifespan. During renumbering it is expected that the old and
that the old and the new prefix co-exist for some time. the new prefix co-exist for some time.
The design of this prefix delegation mechanism meets the requirements The design of this prefix delegation mechanism meets the requirements
for prefix delegation in Requirements for IPv6 prefix delegation [8]. for prefix delegation in Requirements for IPv6 prefix delegation [6].
Note that this use of DHCP is not bound to the assignment of IP
addresses or other configuration information to hosts, and that no
mechanism is currently available to communicate delegated prefixes to
a DHCP server that serves such a function. This may be an item of
future work, should usage warrant.
2. DHCPv6 specification dependency 2. DHCPv6 specification dependency
This document describes new DHCPv6 options for IPv6 prefix This document describes new DHCPv6 options for IPv6 prefix
delegation. This document should be read in conjunction with the delegation. This document should be read in conjunction with the
DHCPv6 specification for a complete specification of the Prefix DHCPv6 specification, RFC 3315 [2], for a complete specification of
Delegation options and mechanism. Definitions for terms and acronyms the Prefix Delegation options and mechanism. Definitions for terms
not specifically defined in this document are defined in the DHCPv6 and acronyms not specifically defined in this document are defined in
specification [6]. RFC 3315.
3. Terminology 3. Terminology
This document uses the terminology defined in RFC2460 [2] and the This document uses the terminology defined in RFC2460 [1] and
DHCP specification [6]. In addition, this document uses the RFC3315. 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.
Identity 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 IA_PD has an prefixes assigned to the requesting router. Each
associated IAID. A requesting router may have more than one IA_PD IA_PD has an associated IAID. A requesting router
assigned to it; for example, one for each of its interfaces. may have more than one IA_PD assigned to it; for
example, one for each of its interfaces.
4. Requirements 4. 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 [3].
5. Model and Applicability 5. Model and Applicability
The model of operation for prefix delegation is as follows. A The model of operation for prefix delegation is as follows. A
delegating router is provided IPv6 prefixes to be delegated to delegating router is provided IPv6 prefixes to be delegated to
requesting routers. Examples of ways in which the delegating router requesting routers. Examples of ways in which the delegating router
may be provided these prefixes are given in Section 12.2. A may be provided these prefixes are given in Section 12.2. A
requesting router requests prefix(es) from the delegating router, as requesting router requests prefix(es) from the delegating router, as
described in Section 12.1. The delegating router chooses prefix(es) described in Section 12.1. The delegating router chooses prefix(es)
for delegation, and responds with prefix(es) to the requesting for delegation, and responds with prefix(es) to the requesting
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| | | Subscriber | | | Subscriber
---+-------------+-----+- -+-----+-------------+--- | network ---+-------------+-----+- -+-----+-------------+--- | network
| | | | | | | | | |
+----+-----+ +-----+----+ +----+-----+ +-----+----+ | +----+-----+ +-----+----+ +----+-----+ +-----+----+ |
|Subscriber| |Subscriber| |Subscriber| |Subscriber| / |Subscriber| |Subscriber| |Subscriber| |Subscriber| /
| PC | | PC | | PC | | PC | / | PC | | PC | | PC | | PC | /
+----------+ +----------+ +----------+ +----------+ / +----------+ +----------+ +----------+ +----------+ /
Figure 1: An example of prefix delegation. Figure 1: An example of prefix delegation.
Figure 1
In this example the delegating router is configured with a set of In this example the delegating router is configured with a set of
prefixes to be used for assignment to customers at the time of each prefixes to be used for assignment to customers at the time of each
customer's first connection to the ISP service. The prefix customer's first connection to the ISP service. The prefix delegation
delegation process begins when the requesting router requests process begins when the requesting router requests configuration
configuration information through DHCP. The DHCP messages from the information through DHCP. The DHCP messages from the requesting
requesting router are received by the delegating router in the router are received by the delegating router in the aggregation
aggregation device. When the delegating router receives the request, device. When the delegating router receives the request, it selects
it selects an available prefi or prefixes for delegation to the an available prefi or prefixes for delegation to the requesting
requesting router. The delegating router then returns the prefix or router. The delegating router then returns the prefix or prefixes to
prefixes to the requesting router. the requesting router.
The requesting router subnets the delegated prefix and assigns the The requesting router subnets the delegated prefix and assigns the
longer prefixes to links in the subscriber's network. In a typical longer prefixes to links in the subscriber's network. In a typical
scenario based on the network shown in Figure 1, the requesting scenario based on the network shown in Figure 1, the requesting
router subnets a single delegated /48 prefix into /64 prefixes and router subnets a single delegated /48 prefix into /64 prefixes and
assigns one /64 prefix to each of the links in the subscriber assigns one /64 prefix to each of the links in the subscriber
network. 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
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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.
6. Identity Association for Prefix Delegation 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. An IA_PD for prefixes is the equivalent configuration information. An IA_PD for prefixes is the equivalent of
of an IA (described in DHCPv6 specification [6]) for addresses. an IA (described in RFC 3315) 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 create at least one distinct one interface. A requesting router must create at least one distinct
IA_PD. It may associate a distinct IA_PD with each of its downstream IA_PD. It may associate a distinct IA_PD with each of its downstream
network interfaces and use that IA_PD to obtain a prefix for that network interfaces and use that IA_PD to obtain a prefix 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 IAIDs on the requesting router. The IAID is unique among the IA_PD IAIDs 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
the requesting router, the IAID for that IA_PD MUST be consistent requesting router, the IAID for that IA_PD MUST be consistent across
across restarts of the requesting router. The requesting router may restarts of the requesting router. The requesting router may maintain
maintain consistency either by storing the IAID in non-volatile consistency either by storing the IAID in non-volatile storage or by
storage or by using an algorithm that will consistently produce the using an algorithm that will consistently produce the same IAID as
same IAID as long as the configuration of the requesting router has long as the configuration of the requesting router has not changed.
not changed. If the requesting router uses only one IAID, it can use If the requesting router uses only one IAID, it can use a well-known
a well-known value, e.g zero. 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 9 for the representation of an IA_PD in a DHCP section Section 9 for the representation of an IA_PD in a DHCP
message. message.
7. Overview of DHCP with Prefix Delegation 7. Overview of DHCP with Prefix Delegation
Prefix delegation with DHCP is independent of address assignment with Prefix delegation with DHCP is independent of address assignment with
DHCP. A requesting router can use DHCP for just prefix delegation or DHCP. A requesting router can use DHCP for just prefix delegation or
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IA_PD option describing the IA_PD. Delegating routers that can IA_PD option describing the IA_PD. Delegating routers that can
delegate prefixes to the IA_PD respond to the requesting router with delegate prefixes to the IA_PD respond to the requesting router with
an Advertise message. an Advertise message.
The requesting router may include prefixes in the IA_PDs as a hint to The requesting router may include prefixes in the IA_PDs as a hint to
the delegating router about specific prefixes for which the the delegating router about specific prefixes for which the
requesting router has a preference. requesting router has a preference.
When the requesting router has identified a delegating router, the When the requesting router has identified a delegating router, the
requesting router uses a Request message to populate the IA_PDs with requesting router uses a Request message to populate the 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
in the Request message. The delegating router returns prefixes and the Request message. The delegating router returns prefixes and other
other information about the IA_PDs to the requesting router in IA_PD information about the IA_PDs to the requesting router in IA_PD
options in a Reply message. The requesting router records the options in a Reply message. The requesting router records the
lifetimes for the delegated prefix(es) and uses the prefix(es) as lifetimes for the delegated prefix(es) and uses the prefix(es) as
described in the previous section. described in the previous section.
Before the valid lifetime on each delegated prefix expires, the Before the valid lifetime on each delegated prefix expires, the
requesting router includes the prefix in an IA_PD option sent in a requesting router includes the prefix in an IA_PD option sent in a
Renew message to the delegating router. The delegating router Renew message to the delegating router. The delegating router
responds by returning the prefix with updated lifetimes to the responds by returning the prefix with updated lifetimes to the
requesting router. requesting router.
8. Interface Selection 8. 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 [6] do not apply. Selection" of RFC 3315 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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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. . . .
. IA_PD-options . . IA_PD-options .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_IA_PD (TBD) option-code: OPTION_IA_PD (TBD)
option-length: 12 + length of IA_PD-options field. option-length: 12 + length of IA_PD-options field.
IAID The unique identifier for this IA_PD; the IAID must be unique IAID: The unique identifier for this IA_PD; the IAID must
among the identifiers for all of this requesting router's IA_PDs. be unique among the identifiers for all of this
requesting router's IA_PDs.
T1 The time at which the requesting router should contact the T1: The time at which the requesting router should
delegating router from which the prefixes in the IA_PD were contact the delegating router from which the
obtained to extend the lifetimes of the prefixes delegated to the prefixes in the IA_PD were obtained to extend the
IA_PD; T1 is a time duration relative to the current time lifetimes of the prefixes delegated to the IA_PD;
T1 is a time duration relative to the current time
expressed in units of seconds. expressed in units of seconds.
T2 The time at which the requesting router should contact any T2: The time at which the requesting router should
available delegating router to extend the lifetimes of the contact any available delegating router to extend
prefixes assigned to the IA_PD; T2 is a time duration relative to the lifetimes of the prefixes assigned to the
the current time expressed in units of seconds. IA_PD; T2 is a time duration relative to the
current time 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_PD are in the IA_PD-options the prefixes associated with this IA_PD are in the IA_PD-options
field. 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
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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
T2 are included to give delegating routers explicit control over when T2 are included to give delegating routers explicit control over when
a requesting router should contact the delegating router about a a requesting router should contact the delegating router about a
specific IA_PD. specific IA_PD.
In a message sent by a requesting router to a delegating router, In a message sent by a requesting router to a delegating router,
values in the T1 and T2 fields indicate the requesting router's values in the T1 and T2 fields indicate the requesting router's
preference for those parameters. The requesting router sets T1 and preference for those parameters. The requesting router sets T1 and T2
T2 to zero if it has no preference for those values. In a message to zero if it has no preference for those values. In a message sent
sent by a delegating router to a requesting router, the requesting by a delegating router to a requesting router, the requesting router
router MUST use the values in the T1 and T2 fields for the T1 and T2 MUST use the values in the T1 and T2 fields for the T1 and T2
parameters. The values in the T1 and T2 fields are the number of parameters. The values in the T1 and T2 fields are the number of
seconds until T1 and T2. seconds until T1 and T2.
The delegating router selects the T1 and T2 times to allow the The delegating router selects the T1 and T2 times to allow the
requesting router to extend the lifetimes of any prefixes in the requesting router to extend the lifetimes of any prefixes in the
IA_PD before the lifetimes expire, even if the delegating router is IA_PD before the lifetimes expire, even if the delegating router is
unavailable for some short period of time. Recommended values for T1 unavailable for some short period of time. Recommended values for T1
and T2 are .5 and .8 times the shortest preferred lifetime of the and T2 are .5 and .8 times the shortest preferred lifetime of the
prefixes in the IA_PD that the delegating router is willing to prefixes in the IA_PD that the delegating router is willing to
extend, respectively. If the time at which the prefixes in an IA_PD extend, respectively. If the time at which the prefixes in an IA_PD
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+-+-+-+-+-+-+-+-+ . +-+-+-+-+-+-+-+-+ .
. IAprefix-options . . IAprefix-options .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code: OPTION_IAPREFIX (TBD) option-code: OPTION_IAPREFIX (TBD)
option-length: 25 + length of IAprefix-options field option-length: 25 + length of IAprefix-options field
preferred-lifetime: The recommended preferred lifetime for the IPv6 preferred-lifetime: The recommended preferred lifetime for the IPv6
prefix in the option, expressed in units of seconds. A value of prefix in the option, expressed in units of
0xFFFFFFFF represents infinity. seconds. A value of 0xFFFFFFFF represents infinity.
valid-lifetime: The valid lifetime for the IPv6 prefix in the option, valid-lifetime: The valid lifetime for the IPv6 prefix in the
expressed in units of seconds. A value of 0xFFFFFFFF represents option, expressed in units of seconds. A value of
infinity. 0xFFFFFFFF represents infinity.
prefix-length: Length for this prefix in bits prefix-length: Length for this prefix in bits
IPv6-prefix: An IPv6 prefix IPv6-prefix: An IPv6 prefix
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 In a message sent by a delegating router the preferred and valid
lifetimes should be set to the values of AdvPreferredLifetime and lifetimes should be set to the values of AdvPreferredLifetime and
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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 In a message sent by a delegating router the preferred and valid
lifetimes should be set to the values of AdvPreferredLifetime and lifetimes should be set to the values of AdvPreferredLifetime and
AdvValidLifetime as specified in section "Router Configuration AdvValidLifetime as specified in section "Router Configuration
Variables" of RFC2461 [3], unless administratively configured. Variables" of RFC2461 [4], unless administratively configured.
A requesting router discards any prefixes for which the preferred A requesting router discards any prefixes for which the preferred
lifetime is greater than the valid lifetime. A delegating router lifetime is greater than the valid lifetime. A delegating router
ignores the lifetimes set by the requesting router if the preferred ignores the lifetimes set by the requesting router if the preferred
lifetime is greater than the valid lifetime and ignores the values lifetime is greater than the valid lifetime and ignores the values
for T1 and T2 set by the requesting router if those values are for T1 and T2 set by the requesting router if those values are
greater than the preferred lifetime. greater than the preferred lifetime.
The values in the preferred and valid lifetimes are the number of The values in the preferred and valid lifetimes are the number of
seconds remaining for each lifetime. seconds remaining for 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.
11. Delegating Router Solicitation 11. 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 RFC
DHCP specification [6]. The details of the solicitation process are 3315. The details of the solicitation process are described in this
described in this section. section.
11.1 Requesting router behaviour 11.1 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 [6]. "Transmission of Solicit Messages" of RFC 3315. The requesting router
The requesting router creates an IA_PD and assigns it an IAID. The creates an IA_PD and assigns it an IAID. The requesting router MUST
requesting router MUST include the IA_PD option in the Solicit 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" of RFC 3315. The
specification [6]. The requesting router MAY choose to consider the requesting router MAY choose to consider the presence of advertised
presence of advertised prefixes in its decision about which 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.
11.2 Delegating router behaviour 11.2 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 [6]. If the message contains an messages" of RFC 3315. If the message contains an IA_PD option and
IA_PD option and the delegating router is configured to delegate the delegating router is configured to delegate prefix(es) to the
prefix(es) to the requesting router, the delegating router selects requesting router, the delegating router selects the prefix(es) to be
the prefix(es) to be delegated to the requesting router. The delegated to the requesting router. The mechanism through which the
mechanism through which the delegating router selects prefix(es) for delegating router selects prefix(es) for delegation is not specified
delegation is not specified in this document. Examples of ways in in this document. Examples of ways in which the delegating router
which the delegating router might select prefix(es) for a requesting might select prefix(es) for a requesting router include: static
router include: static assignment based on subscription to an ISP; assignment based on subscription to an ISP; dynamic assignment from a
dynamic assignment from a pool of available prefixes; selection based pool of available prefixes; selection based on an external authority
on an external authority such as a RADIUS server using the Framed- such as a RADIUS server using the Framed-IPv6-Prefix option as
IPv6-Prefix option as described in RFC 3162 [7]. described in RFC 3162 [5].
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 [6]. transmission of Advertise messages" of RFC 3315. The delegating
The delegating router MUST include an IA_PD option, identifying any router MUST include an IA_PD option, identifying any prefix(es) that
prefix(es) that the delegating router will delegate to the requesting 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 the IA_PD with no prefixes in the IA_PD and a Status Code includes the IA_PD with no prefixes in the IA_PD and a Status Code
option in the IA_PD containing status code NoPrefixAvail and a status option in the IA_PD containing status 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.
12. Requesting router initiated prefix delegation 12. 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 RFC 3315 to
specification [6] to obtain or update prefix(es) from a delegating obtain or update prefix(es) from a delegating router. The requesting
router. The requesting router and the delegating router use the router and the delegating router use the IA_PD Prefix option to
IA_PD Prefix option to exchange information about prefix(es) in much exchange information about prefix(es) in much the same way IA Address
the same way IA Address options are used for assigned addresses. options are used for assigned addresses.
12.1 Requesting router behaviour 12.1 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
in the Request message. The delegating router then returns the the Request message. The delegating router then returns the prefixes
prefixes for the IA_PDs to the requesting router in IA_PD options in for the IA_PDs to the requesting router in IA_PD options in a Reply
a Reply message. 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 includes messages sent by the requesting router. The IA_PD option includes all
all of the prefixes the requesting router currently has associated of the prefixes the requesting router currently has associated with
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
ask for such verification include: 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
Rebind/Reply message exchange as described in the section "Creation Rebind/Reply message exchange as described in the section "Creation
and Transmission of Rebind Messages" of the DHCP specification [6], and Transmission of Rebind Messages" of RFC 3315, with the exception
with the exception that the retransmission parameters should be set that the retransmission parameters should be set as for the Confirm
as for the Confirm message, described in the section "Creation and message, described in the section "Creation and Transmission of
Transmission of Confirm Messages" of the DHCP specification [6]. The Confirm Messages" of RFC 3315. The requesting router includes any
requesting router includes any IA_PDs, along with prefixes associated IA_PDs, along with prefixes associated with those IA_PDs in its
with those IA_PDs in its Rebind message. Rebind message.
Each prefix has valid and preferred lifetimes whose durations are Each prefix has valid and preferred lifetimes whose durations are
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.
skipping to change at page 14, line 30 skipping to change at page 14, line 30
3FFE:FFFF:0:2::/64 for assignment to the two links in the subscriber 3FFE:FFFF:0:2::/64 for assignment to the two links in the subscriber
network. If the requesting router were delegated 3FFE:FFFF:0::/48 network. If the requesting router were delegated 3FFE:FFFF:0::/48
and 3FFE:FFFF:5::/48, it might assign 3FFE:FFFF:0:1::/64 and and 3FFE:FFFF:5::/48, it might assign 3FFE:FFFF:0:1::/64 and
3FFE:FFFF:5:1::/64 to one of the links, and 3FFE:FFFF:0:2::/64 and 3FFE:FFFF:5:1::/64 to one of the links, and 3FFE:FFFF:0:2::/64 and
3FFE:FFFF:5:2::/64 for assignment to the other link. 3FFE:FFFF:5:2::/64 for assignment to the other link.
If the requesting router assigns a delegated prefix to a link to If the requesting router assigns a delegated prefix to a link to
which the router is attached, and begins to send router which the router is attached, and begins to send router
advertisements for the prefix on the link, the requesting router MUST advertisements for the prefix on the link, the requesting router MUST
set the valid lifetime in those advertisements to be no later than set the valid lifetime in those advertisements to be no later than
the valid lifetime specified in the IA_PD Prefix option. A the valid lifetime specified in the IA_PD Prefix option. A requesting
requesting router MAY use the preferred lifetime specified in the router MAY use the preferred lifetime specified in the IA_PD Prefix
IA_PD Prefix option. option.
Handling of Status Codes options in received Reply messages is Handling of Status Codes options in received Reply messages is
described in "Receipt of Reply Messages" of the DHCP specification described in "Receipt of Reply Messages" of RFC 3315. The
[6]. The NoPrefixAvail Status Code is handled in the same manner as NoPrefixAvail Status Code is handled in the same manner as the
the NoAddrsAvail Status Code. NoAddrsAvail Status Code.
12.2 Delegating Router behaviour 12.2 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. The mechanism through which the delegating router requesting router. The mechanism through which the delegating router
selects prefix(es) for delegation is not specified in this document. selects prefix(es) for delegation is not specified in this document.
Section 11.2 gives examples of ways in which a delegating router Section 11.2 gives examples of ways in which a delegating router
skipping to change at page 15, line 14 skipping to change at page 15, line 14
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 finds that any from the requesting router. If the delegating router finds that any
of the prefixes are not in the requesting router's binding entry, the of the prefixes are not in the requesting router's binding entry, the
delegating router returns the prefix to the requesting router with delegating router returns the prefix to the requesting router with
lifetimes of 0. lifetimes of 0.
Behaviour in the case where the delegating router cannot find a Behaviour in the case where the delegating router cannot find a
binding for the requesting router's IA_PD: binding for the requesting router's IA_PD:
Renew message If the delegating router cannot find a binding for the Renew message: If the delegating router cannot find a binding
requesting router's IA_PD the delegating router returns the IA_PD for the requesting router's IA_PD the delegating
containing no prefixes with a Status Code option set to NoBinding router returns the IA_PD containing no prefixes
in the Reply message. with a Status Code option set to NoBinding in the
Reply message.
Rebind message If the delegating router cannot find a binding for the Rebind message: If the delegating router cannot find a binding
requesting router's IA_PD and the delegating router determines for the requesting router's IA_PD and the
that the prefixes in the IA_PD are not appropriate for the link to delegating router determines that the prefixes in
which the requesting router's interface is attached according to the IA_PD are not appropriate for the link to
the delegating routers explicit configuration, the delegating which the requesting router's interface is
router MAY send a Reply message to the requesting router attached according to the delegating routers
containing the IA_PD with the lifetimes of the prefixes in the explicit configuration, the delegating router MAY
IA_PD set to zero. This Reply constitutes an explicit send a Reply message to the requesting router
notification to the requesting router that the prefixes in the containing the IA_PD with the lifetimes of the
IA_PD are no longer valid. If the delegating router is unable to prefixes in the IA_PD set to zero. This Reply
determine if the prefix is not appropriate for the link, the constitutes an explicit notification to the
Rebind message is discarded. requesting router that the prefixes in the IA_PD
are no longer valid. If the delegating router is
unable to determine if the prefix is not
appropriate for the link, the Rebind message is
discarded.
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.
The delegating router MUST include an IA_PD Prefix option or options The delegating router MUST include an IA_PD Prefix option or options
(in an IA_PD option) in Reply messages sent to a requesting router. (in an IA_PD option) in Reply messages sent to a requesting router.
13. Prefix Delegation reconfiguration 13. Prefix Delegation reconfiguration
skipping to change at page 15, line 46 skipping to change at page 16, line 4
The delegating router MUST include an IA_PD Prefix option or options The delegating router MUST include an IA_PD Prefix option or options
(in an IA_PD option) in Reply messages sent to a requesting router. (in an IA_PD option) in Reply messages sent to a requesting router.
13. Prefix Delegation reconfiguration 13. Prefix Delegation reconfiguration
This section describes prefix delegation in Reconfigure message This section describes prefix delegation in Reconfigure message
exchanges. exchanges.
13.1 Delegating Router behaviour 13.1 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
Initiated Configuration Exchange" of the DHCP specification [6]. The Server-Initiated Configuration Exchange" of RFC 3315. The delegating
delegating router specifies the IA_PD option in the Option Request router specifies the IA_PD option in the Option Request option to
option to cause the requesting router to include an IA_PD option to cause the requesting router to include an IA_PD option to obtain new
obtain new information about delegated prefix(es). information about delegated prefix(es).
13.2 Requesting Router behaviour 13.2 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 [6]. The a delegating router as described in RFC 3315. The requesting router
requesting router MUST include the IA_PD Prefix option(s) (in an MUST include the IA_PD Prefix option(s) (in an IA_PD option) for
IA_PD option) for prefix(es) that have been delegated to the prefix(es) that have been delegated to the requesting router by the
requesting router by the delegating router from which the Reconfigure delegating router from which the Reconfigure message was received.
message was received.
14. Relay agent behaviour 14. 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 RFC
specification [6]. 3315.
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.
15. Security Considerations 15. 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 [6]. "Security Considerations" of RFC 3315.
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.
A malicious requesting router may be able to mount a denial of A malicious 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" of RFC 3315.
specification [6]. For point to point links, where one trusts that For point to point links, where one trusts that there is no man in
there is no man in the middle, or one trusts layer two the middle, or one trusts layer two authentication, DHCP
authentication, DHCP authentication or IPsec may not be necessary. authentication or IPsec may not be necessary. Because a requesting
Because a requesting router and delegating routers must each have at router and delegating routers must each have at least one assigned
least one assigned IPv6 address, the routers may be able to use IPsec IPv6 address, the routers may be able to use IPsec for authentication
for authentication of DHCPv6 messages. The details of using IPsec of DHCPv6 messages. The details of using IPsec for DHCPv6 are under
for DHCPv6 are under development. development.
Networks configured with delegated prefixes should be configured to
preclude intentional or inadvertent inappropriate advertisement of
these prefixes.
16. IANA Considerations 16. IANA Considerations
IANA is requested to assign option codes to: IANA is requested to assign option codes to:
OPTION_IA_PD OPTION_IA_PD
OPTION_IAPREFIX OPTION_IAPREFIX
from the option-code space as defined in section "DHCPv6 Options" of from the option-code space as defined in section "DHCPv6 Options" of
the DHCPv6 specification [6]. RFC 3315.
IANA is requested to assign a status code: IANA is requested to assign a status code:
NoPrefixAvail Delegating router has no prefixes available to assign NoPrefixAvail: Delegating router has no prefixes available to
to the IAPD(s) assign to the IAPD(s)
from the status-code space as defined in section "Status Codes" of from the status-code space as defined in section "Status Codes" of
the DHCPv6 specification [6]. RFC 3315.
17. Acknowledgements 17. 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, Trevor Warwick and Toshi Yamasaki. Pekka Savola, Bernie Volz, Trevor Warwick and Toshi Yamasaki.
18. Changes in draft-ietf-dhc-dhcpv6-opt-prefix-delegation-03
o Clarified that this draft is an extension of the DHCPv6
specification and that complete specification and terminology can
be found in the DHCPv6 specification.
o Updated relevant sections to be consistent with draft-ietf-dhc-
dhcpv6-interop-00.txt. This includes T1/T2 times, preferred and
valid lifetimes and Rebind/Renew usage.
o Clarified the usage of the NoPrefixAvail Status Code
o Clarified delegating router behaviour when no binding is found for
Renew/Rebind.
o Various editorial changes
Normative References Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Levels", BCP 14, RFC 2119, March 1997.
[2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 2460, December 1998. Specification", RFC 2460, December 1998.
[3] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for [2] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
IP Version 6 (IPv6)", RFC 2461, December 1998. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003.
[4] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[5] Thomson, S. and T. Narten, "IPv6 Stateless Address [3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Autoconfiguration", RFC 2462, December 1998. Levels", BCP 14, RFC 2119, March 1997.
[6] Droms, R., "Dynamic Host Configuration Protocol for IPv6 [4] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
(DHCPv6)", draft-ietf-dhc-dhcpv6-28 (work in progress), November IP Version 6 (IPv6)", RFC 2461, December 1998.
2002.
[7] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC 3162, [5] Aboba, B., Zorn, G. and D. Mitton, "RADIUS and IPv6", RFC 3162,
August 2001. August 2001.
Informative References Informative References
[6] Miyakawa, S. and R. Droms, "Requirements for IPv6 prefix
[8] Miyakawa, S., "Requirements for IPv6 prefix delegation", draft- delegation", draft-ietf-ipv6-prefix-delegation-requirement-03
ietf-ipv6-prefix-delegation-requirement-00 (work in progress), (work in progress), August 2003.
November 2002.
Authors' Addresses Authors' Addresses
Ole Troan Ole Troan
Cisco Systems Cisco Systems
250 Longwater Avenue 250 Longwater Avenue
Reading RG2 6GB Reading RG2 6GB
United Kingdom United Kingdom
Phone: +44 20 8824 8666 Phone: +44 20 8824 8666
skipping to change at page 19, line 5 skipping to change at page 19, line 5
Ralph Droms Ralph Droms
Cisco Systems Cisco Systems
1414 Massachusetts Avenue 1414 Massachusetts Avenue
Boxborough, MA 01719 Boxborough, MA 01719
USA USA
Phone: +1 978 936-1674 Phone: +1 978 936-1674
EMail: rdroms@cisco.com EMail: rdroms@cisco.com
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