Mobile IPv6 Extensions Group R. Droms
Internet-Draft P. Thubert
Intended status: Standards Track Cisco
Expires: September 7, 2009 F. Dupont
ISC
W. Haddad
Qualcomm
March 6, 2009
DHCPv6 Prefix Delegation for NEMO
draft-ietf-mext-nemo-pd-02
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 7, 2009.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Droms, et al. Expires September 7, 2009 [Page 1]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
Abstract
One aspect of network mobility support is the assignment of a prefix
or prefixes to a Mobile Router (MR) for use on the links in the
Mobile Network. DHCPv6 prefix delegation can be used for this
configuration task.
1. Introduction
One aspect of network mobility support is the assignment of a prefix
or prefixes to a Mobile Router for use on the links in the Mobile
Network. DHCPv6 prefix delegation [RFC3633] (DHCPv6PD) can be used
for this configuration task.
2. Terminology
The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be
interpreted as described in RFC2119 [RFC2119].
The following terms used in this document are defined in the IPv6
Addressing Architecture document [RFC4291]:
link-local unicast address
link-local scope multicast address
The following terms used in this document are defined in the mobile
IPv6 specification [RFC3775]:
home agent (HA)
home link
The following terms used in this document are defined in the Mobile
Network terminology document [RFC4886]:
Mobile Router (MR)
Mobile Network
mobile host (MH)
The following terms used in this document are defined in the DHCPv6
[RFC3315] and DHCPv6 prefix delegation [RFC3633] specifications:
Droms, et al. Expires September 7, 2009 [Page 2]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
delegating router (DR; acts as a DHCPv6 server)
requesting router (RR; acts as a DHCPv6 client)
DHCPv6 relay agent
The following acronym is used in this document:
DHCPv6PD: DHCPv6 prefix delegation
3. Application of DHCPv6 prefix delegation to mobile networks for
delegation of home prefixes
The NEMO Basic protocol [RFC3963] extends the mobile IPv6 protocol
[RFC3775] to enable network mobility. In this extension, a MR uses
the mobile IPv6 protocol to establish and maintain a session with its
HA, and uses bidirectional tunneling between the MR and HA to provide
a path through which nodes attached to links in the Mobile Network
can maintain connectivity with nodes not in the Mobile Network.
The requirements for NEMO [RFC4885] include the ability of the MR to
receive delegated prefixes that can then be assigned to links in the
Mobile Network. DHCPv6PD can be used to meet this requirement for
prefix delegation.
To use DHCPv6PD for Mobile Networks, the HA assumes the role of
either the DR or a DHCPv6 relay agent and the MR assumes the role of
the RR. Throughout the remainder of this document, the HA will be
assumed to be acting as a DHCPv6PD DR or relay agent and the MR will
be assumed to be acting as a RR.
If the HA is acting as relay agent, some other device acts as the DR.
For example, the server providing DHCPv6 service in the home network
might also provide NEMO DHCPv6PD service. Or, a home network with
several HAs might configure one of those HAs as a DHCPv6PD server
while the other HAs act as relay agents.
The HA and MR exchange DHCPv6PD protocol messages through the tunnel
connecting them. The tunnel acts as the link labeled "DSL to
subscriber premises" in figure 1 of the DHCPv6PD specification.
The DHCPv6PD server is provisioned with prefixes to be assigned using
any of the prefix assignment mechanisms described in the DHCPv6PD
specifications. Other updates to the HA data structures required as
a side effect of prefix delegation are specified by the particular
network mobility protocol. For example, in the case of Basic Network
Mobility Support [RFC3963], the HA would add an entry in its binding
Droms, et al. Expires September 7, 2009 [Page 3]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
cache registering the delegated prefix to the MR to which the prefix
was delegated.
3.1. When the MR uses DHCPv6
The MR initiates a DHCPv6 message exchange for prefix delegation
whenever it establishes an MR-HA tunnel to its HA. If the MR does
not have any active delegated prefixes (with unexpired leases), the
MR initiates a DHCPv6 message exchange with a DHCPv6 Solicit message
as described in section 17 of RFC 3315 and section 12.1 of RFC 3633.
If the MR has one or more active delegated prefixes, the MR initiates
a DHCPv6 message exchange with a DHCPv6 Rebind message as described
in section 18.1.2 of RFC 3315 and section 12.1 of RFC 3633.
3.2. Use of MR-HA tunnel for DHCPv6 messages
The DHCPv6 specification requires the use of link-local unicast and
link-local scope multicast addresses in DHCPv6 messages (except in
certain cases as defined in section 22.12 of the DHCPv6
specification). Section 10.4.2 of the mobile IPv6 specification
describes forwarding of intercepted packets, and the third paragraph
of that section begins:
However, packets addressed to the mobile node's link-local address
MUST NOT be tunneled to the mobile node.
The DHCPv6 messages exchanged between the HA and the MR originate
only with the HA and the MR, and therefore are not "intercepted
packets" and may be sent between the HA and the MR through the
tunnel.
Even though the MR-HA tunnel is a point to point connection, the MR
SHOULD use multicast DHCPv6 messages as described in RFC 3315 over
that tunnel.
3.3. DHCPv6 Relay Agent for transmission of DHCPv6 messages
A DHPCv6 relay agent function [RFC3315] can be used as an alternative
to multicast DHCPv6 messages over the tunnel between the MR and the
HA. In this configuration, the relay agent function is co-located in
the MR with the DHCPv6 client function. Rather than using multicast
to send DHCPv6 messages through the tunnel to the DHCPv6 server, the
DHCPv6 client in the MR hands any outbound DHCPv6 messages to the co-
located relay agent. Responses from the DHCPv6 server are delivered
to the relay agent function in the MR, which extracts the
encapsulated message and delivers it to the DHCPv6 client in the MR.
Droms, et al. Expires September 7, 2009 [Page 4]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
3.3.1. Relay agent configuration
The use of the relay agent function in the MR allows the MR to
unicast DHCPv6 messages to the DHCPv6 server. The relay agent must
be configured with the address of the DHCPv6 server or another DHCPv6
relay agent that will forward message on to a DHCPv6 server. For the
purposes of NEMO, the relay agent assumes that the HA for the MR
hosts the next hop in the path the to the DHCPv6 server: either the
DHCPv6 server or a relay agent that will forward message to the
DHCPv6 server. Therefore, if the MR acts as a DHCPv6 relay agent,
the MR MUST configure the DHCPv6 relay agent to forward DHCPv6
messages to the HA.
3.3.2. Transmission of DHCPv6 messages
In this configuration, when the DHCPv6 client in the MR sends a
message, it hands the message to the DHCPv6 relay agent in the MR.
The way in which this handoff takes place is beyond the scope of this
document. The relay agent encapsulates the message from the client
according to RFC 3315 in a Relay-forward message and sends the
resulting DHCPv6 message to the HA. The relay agent sets the fields
in the Relay-forward message as follows:
msg-type RELAY-FORW
hop-count 1
link-address A non-link-local address from the MR interface to the
tunnel between the HA and MR
peer-address A non-link-local address from the MR interface to the
tunnel between the HA and MR
options MUST include a "Relay Message option" [RFC3315]; MAY
include other options added by the relay agent.
3.3.3. Receipt of DHCPv6 messages
In this configuration, messages from the DHCPv6 server will be
returned to the DHCPv6 relay agent, with the message for the DHCPv6
client encapsulated in the Relay Message option [RFC3315] in a Relay-
reply message. The relay agent function extracts the message for the
client from the Relay Message option and hands the message to the
DHCPv6 client in the MR. The way in which this handoff takes place
is beyond the scope of this document.
Droms, et al. Expires September 7, 2009 [Page 5]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
3.4. Exchanging DHCPv6 messages when MR is at home
When the MR is on its home link, the HA uses the home link to
exchange DHCPv6PD messages with the MR. It is the responsibility of
the implementation to determine when the MR is on its home link and
to avoid use of any existing tunnel.
3.5. Selecting an HA that provides DHCPv6PD
Not all nodes that are willing to act as an HA are required to
provide DHCPv6PD. Therefore, when selecting an HA, a MR that
requires DHCPv6PD service must identify an HA that will provide the
service. The MR can determine if an HA provides DHCPv6PD by
initiating a DHCPv6 message exchange in which the MR requests
delegated prefix(es). If the HA does not respond or responds but
does not delegate any prefix(es) in its response, the MR assumes that
the HA does not provide DHCPv6PD service. The MR continues to query
all candidate HAs until it finds an HA that provides DHCPv6PD.
Querying an HA to determine if it provides DHCPv6PD requires a small
modification to the operation of DHCPv6 as described in RFC 3315.
Under normal circumstances, a host will continue to send DHCPv6
Solicit messages until it receives a response (see Section 17 of RFC
3315). However, an HA may choose not to respond to the Solicit
messages from the MR because the HA does not provide DHCPv6.
Therefore, when querying an HA to determine if the HA provides
DHCPv6PD service, the MR MUST discontinue sending Solicit messages to
the HA after sending 6 Solicit messages, and conclude that the HA
will not provide DHCPv6PD service.
The MR may choose to probe the HAs for DHCPv6PD service sequentially
or in parallel.
3.6. Minimizing DHCPv6PD messages
DHCPv6PD in a Mobile Network can be combined with the Rapid Commit
option [RFC3315] to provide DHCPv6 prefix delegation with a two
message exchange between the mobile node and the DHCPv6PD DR.
3.7. Location of DHCPv6PD Delegating Router function
Support of DHCPv6PD for a Mobile Network is optional.
The use of a DHCPv6 relay agent in DHCPv6PD may require "a protocol
or other out-of-band communication to add routing information for
delegated prefixes into the provider edge router" (section 14 of RFC
3633). If the DHCPv6PD DR function is implemented in the HA for the
MR, no relay agent function is required.
Droms, et al. Expires September 7, 2009 [Page 6]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
It may be desirable to use a single DR to manage RRs in a network
with multiple HAs. In this scenario, the HAs will act as DHCP relay
agents, forwarding messages between the RRs and the DR.
Use of the DHCPv6 relay agent function with DHCPv6PD requires that
there be some mechanism through which routing information for the
delegated prefixes can be added to the appropriate routing
infrastructure. If the HA is acting as a DHCPv6 relay agent, the HA
SHOULD add a route to the delegated prefix and advertise that route
after receiving a binding update for the prefix from the RR
[RFC3963].
In particular, if the MR uses NEMO explicit mode, then it must add
the delegated prefix to the prefix list in the Binding Update
messages. If the binding cache is cleared before the prefix valid
lifetime, the MR might bind that prefix again using explicit mode,
till the lifetime expires.
In implicit mode, the HA must save the delegated prefix with the
binding cache entry (BDE) of the Mobile Router. When the BCE is
cleared, the HA loses the information about the delegated prefix.
Because the MR will use DHCPv6 when it reestablishes its tunnel to
the HA (see Section 3.1), the HA will be able to add the delegated
prefix back to the BCE.
At the time this draft was written, one way in which a DR can
explicitly notify a relay agent about delegated prefixes, is to use
the "DHCP Relay Agent Assignment Notification Option"
[I-D.ietf-dhc-dhcpv6-agentopt-delegate].
Another alternative, if the RR is part of the same administrative
domain as the home network to which it is attached through the HA,
and the RR can be trusted, the RR can use a routing protocol like
OSPF to advertise any delegated prefixes.
NEMO explicit mode is recommended to take advantage of the function
already defined for NEMO.
3.8. Other DHCPv6 functions
The DHCPv6 messages exchanged between the MR and the HA may also be
used for other DHCPv6 functions in addition to DHCPv6PD. For
example, the HA may assign global addresses to the MR and may pass
other configuration information such as a list of available DNS
recursive name servers [RFC3646] to the MR using the same DHCPv6
messages as used for DHCPV6PD.
The HA may act as a DHCPv6 relay agent for MHs while it acts as a DR
Droms, et al. Expires September 7, 2009 [Page 7]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
for MRs.
4. Security Considerations
This document describes the use of DHCPv6 for prefix delegation in
Mobile Networks. It does not introduce any additional security
considerations for DHCPv6 beyond those described in the "Security
Considerations" section of the DHCPv6 base specification [RFC3315]
and the "Security Considerations" of the DHCPv6 Prefix Delegation
specification [RFC3633].
The use of DHCPv6, as described in this document, requires only
message integrity protection, which can be provided by the mobile
network infrastructure between the MR and the HA.
If the network infrastructure connecting the various communicating
nodes does not provide message integrity and source authentication
for the DHCPv6PD messages, HAs and MRs SHOULD use DHCPv6
authentication as described in section "Authentication of DHCP
messages" of the DHCPv6 specification [RFC3315], to guard against
attacks mounted through prefix delegation.
If the HA and DHCPv6 PD functions are not provided by the same
physical node, the HA will act as a DHCPv6 relay agent between the MR
and the DHCPv6 server. In this scenario, the mobile network
infrastructure will only protect the DHCPv6 traffic between the RR
(MR) and the relay agent (HA). The following text, based on Section
21.1 of RFC 3315, describes how appropriate security can be provided
between a DHCPv6 relay agent and server.
DHCPv6 relay agents and servers MAY use IPsec mechanisms for IPv6
[RFC2401] to exchange messages securely. DHCPv6 relay agents and
servers that support secure relay agent to server or relay agent
to relay agent communication use IPsec under the following
conditions:
Selectors DHCPv6 relay agents are manually configured with
the addresses of the DHCPv6 server to which DHCPv6
messages are to be forwarded. Each DHCPv6 server
that will be using IPsec for securing DHCPv6
messages must also be configured with a list of
the DHCPv6 relay agents to which messages will be
returned. The selectors for the DHCPv6 relay
agents and servers will be the pairs of addresses
defining DHCPv6 relay agents and servers that
exchange DHCP messages on the DHCPv6 UDP ports 546
and 547.
Droms, et al. Expires September 7, 2009 [Page 8]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
Mode DHCPv6 relay agents and servers use transport mode
and ESP. The information in DHCPv6 messages is
not generally considered confidential, so
encryption need not be used (i.e., NULL encryption
can be used).
Key management If the HA providing the DHCPv6 relay agent
function and the DHCPv6 servers are both
administered by the same organization, public key
schemes are not necessary. Because the relay
agents and servers must be manually configured,
manually configured key management may suffice,
but does not provide defense against replayed
messages. Accordingly, IKE with preshared secrets
SHOULD be supported.
Discussion: If NEMO may be deployed with the HA
and the DHCPv6 server in different
administrative domains, this text
should be extended to include the use
of IKE with public keys.
Security policy DHCPv6 messages between relay agents and servers
should only be accepted from DHCPv6 peers as
identified in the local configuration.
Authentication Shared keys, indexed to the source IP address of
the received DHCPv6 message, are adequate in this
application.
5. IANA Considerations
This document describes the use of DHCPv6 for prefix delegation in
Mobile Networks. It does not introduce any additional IANA
considerations.
6. Change Log
This section MUST be removed before this document is published as an
RFC.
6.1. Revision -00
This document is based on draft-ietf-nemo-dhcpv6-pd-03 and includes
the use of the DHCPv6 relay agent in the MR, as described in
Section 3.3, from draft-dupont-mext-dhcrelay-00.
Droms, et al. Expires September 7, 2009 [Page 9]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
6.2. Revision -01
Added detail in Section 4, "Security Considerations", describing
protection required for DHCPv6 and a mechanism for protecting traffic
between the DHCPv6 relay agent and server.
Corrected minor typos.
6.3. Revision -02
Removed text describing extensions to DHAAD for discovery of HA that
will provide PD.
Added Section 3.5, "Selecting an HA that provides DHCPv6PD," which
describes how an MR can discover DHCPv6PD service through polling of
multiple HAs.
Added text to Section 4, "Security Considerations", giving detail
about the use of IPsec.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3646] Droms, R., "DNS Configuration options for Dynamic Host
Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
December 2003.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
[RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
Thubert, "Network Mobility (NEMO) Basic Support Protocol",
Droms, et al. Expires September 7, 2009 [Page 10]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
RFC 3963, January 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
7.2. Informative References
[RFC4885] Ernst, T. and H-Y. Lach, "Network Mobility Support
Terminology", RFC 4885, July 2007.
[RFC4886] Ernst, T., "Network Mobility Support Goals and
Requirements", RFC 4886, July 2007.
[I-D.ietf-dhc-dhcpv6-agentopt-delegate]
Droms, R. and B. Volz, "DHCPv6 Relay Agent Assignment
Notification (RAAN) Option",
draft-ietf-dhc-dhcpv6-agentopt-delegate-03 (work in
progress), February 2009.
Authors' Addresses
Ralph Droms
Cisco
1414 Massachusetts Avenue
Boxborough, MA 01719
USA
Phone: +1 978.936.1674
Email: rdroms@cisco.com
Pascal Thubert
Cisco
Village d'Entreprises Green Side
400, Avenue Roumanille
Biot - Sophia Antipolis 06410
FRANCE
Email: pthubert@cisco.com
Francis Dupont
ISC
Email: Francis.Dupont@fdupont.fr
Droms, et al. Expires September 7, 2009 [Page 11]
Internet-Draft DHCPv6 Prefix Delegation for NEMO March 2009
Wassim Haddad
Qualcomm
Email: whaddad@qualcomm.com
Droms, et al. Expires September 7, 2009 [Page 12]
