One document matched: draft-zhao-dhc-dhcpv6-relay-link-selection-00.txt
DHC Working Group Amy. Zhao
Internet-Draft Huawei Technologies Co.,Ltd
Expires: March 16, 2007 September 12, 2006
DHCPv6 Relay Agent Link Selection(RALS) Option
draft-zhao-dhc-dhcpv6-relay-link-selection-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document defines a new Relay Agent Link Selection(RALS) option
for the Dynamic Host Configuration Protocol for IPv6 (DHCPv6).The new
option is inserted by the DHCPv6 relay agent when forwarding client-
originated DHCPv6 packets to a DHCPv6 server. Servers recognizing
this new option can include link-selection information as part of
policies about address assignment, prefix delegation, or other DHCP
parameters.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Terminology . . . . . . . . . . . . . . . . . . . 5
3. The Relay Agent Link Selection Option . . . . . . . . . . . . 6
3.1. Encapsulated IA Address option . . . . . . . . . . . . . . 7
3.2. Encapsulated IA Prefix option . . . . . . . . . . . . . . 7
4. DHCPv6 Relay Agent Behavior . . . . . . . . . . . . . . . . . 9
4.1. Relaying a Message from a client . . . . . . . . . . . . . 9
4.2. Relaying a Message from a Relay Agent . . . . . . . . . . 9
5. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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1. Introduction
Dynamic Host Configuration Protocol for IPv6(DHCPv6) [RFC3315]
provides IP addresses and configuration information for IPv6
clients.It includes a relay agent capability in which processes
within the network infrastructure receive multicast messages from
clients and relay them to DHCPv6 servers.
In some network environments, it will be useful for the relay agent
to add information to the DHCPv6 message before relaying it. The
information that relay agents supply can also be used in the server's
decision-making about the addresses and configuration parameters that
the client is to receive.
In the usual approach, when the DHCPv6 relay agent relays the request
from a client, it constructs a new DHCPv6 Relay-forward message and
places a global or site-scoped address with a prefix assigned to the
link on which the client should be assigned an address in the 'link-
address' field. This address will be used by the server to determine
the link from which the client should be assigned an address and
other configuration information.
However, some situations exist where the relay agent needs to be able
to communicate to the DHCPv6 server the link/subnet from which to
allocate IP address(es) or delegate prefix(es).
For example:
In a NETLMM infrastructure[I-D.giaretta-netlmm-dt], if the mobile
node(MN) uses DHCPv6 to request the address, the Moblie Access
Gateway(MAG) acts as DHCPv6 Relay Agent and connects to the DHCPv6
Server.
When MN powers on or connects to a NETLMM domain, the MAG includes
the identifier of the Local Mobility Anchor(LMA) that is in charge of
serving that MN in the DHCPv6 Relay-forward message, so that the
DHCPv6 server can select the IP address accordingly(e.g. from the IP
subnet of the LMA).
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+--------------------------------+
| LMM Domain |
| |
| +----+ +----+ |
| |LMA | | LMA| |
| +----+ +----+ |
| \ / |
| ********************** |
| * * |
| * IP network * |
| * * |
| ********************** |
| / | \ |
| +----+ +----+ +----+ |
+--|MAG1|----|MAG2|-----|MAG3|---+
+----+ +----+ +----+
| |
| |
+---+ Movement +--+
|MN | ----> |CN|
+---+ +--+
Figure 1 - Reference architecture
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2. Requirements 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].
NETLMM terminology in this document follows that in[I-D.giaretta-
netlmm-dt] .
Definitions for terms and acronyms used in this document are defined
in [RFC3315].
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3. The Relay Agent Link Selection Option
The RALS option carries information about a list of selected links/
subnets from which the client may be assigned address(es)/prefix(es).
It encapsulates IA Address options([RFC3315]) or IA prefix
options([RFC3633]).
The new option is inserted by the DHCPv6 relay agent when forwarding
client-originated DHCPv6 packets to a DHCPv6 server. Servers
recognizing the RALS option may use the information to implement
address/prefix or other parameter assignment policies.
The RALS option is only exchanged between the DHCPv6 relay agent and
the DHCPv6 Server, the DHCPv6 Client MUST NOT insert this option into
the area of DHCPv6 request messages.
The DHCPv6 Relay agent and DHCPv6 server MUST ignore the RALS option
that comes from the DHCPv6 client.
The format of the DHCPv6 RALS option is shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encapsulated-options .
| |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 - RALS option format
option-code
TBD. This is the DHCPv6 option code for the RALS option
option-len
An unsigned integer giving the length of the option data field in
octets.
encapsulated-options
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DHCPv6 options to be delivered by the RALS option. The contents
of options encapsulated in the RALS option are interpreted
according to the use of those options in the relay agent . The
uses of the DHCP IA Address and IA Prefix options in the RALS
options are defined in this document.
3.1. Encapsulated IA Address option
The fields in an IA Address option (OPTION_IAADDR, option code 5) are
used as follows:
IPv6 address
The IPv6 address of the selected link/subnet
preferred-lifetime
Not used
valid-lifetime
Not used
IAaddr-options
Not used
3.2. Encapsulated IA Prefix option
The fields in an IA Prefix option (OPTION_IAPREFIX, option code 28)
are used as follows:
preferred-lifetime
Not used
valid-lifetime
Not used
prefix-length
length for this prefix in bits
IPv6-prefix
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The IPv6 prefix of the selected link/subnet
IAaddr-options
Not used
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4. DHCPv6 Relay Agent Behavior
Adding of the DHCPv6 RALS Option SHOULD be configurable, and MUST be
disabled by default.
How the relay agent learns the link/subnet information is outside the
scope of this document.
4.1. Relaying a Message from a client
When a relay agent receives a valid DHCPv6 message to be relayed from
a client, it constructs a new Relay-forward message per Section
20.1.1 of [RFC3315] and then adds the RALS option to the Relay-
forward message, along with other option(s), e.g. the Interface-Id
option, if it is configured to do so.
4.2. Relaying a Message from a Relay Agent
When a relay agent receives a valid Relay-forward message from
another relay agent closer to the client, if the message already
includes a RALS option in the area of Relay-forward message, the
relay agent MUST NOT add another RALS Option,else the relay agent
shall construct a new Relay-forward message per Section 20.1.2 of
[RFC3315] and then add the RALS Option to this newly created Relay-
forward message, along with other option(s), as described in Section
3.1.1 of [RFC3315], if it is configured to do so.
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5. DHCPv6 Server Behavior
This option provides additional information to the DHCPv6 server.
When the DHCPv6 server receives a message from a relay agent
containing a RALS option,if it is configured to support this option,
it extracts the contents of the option and SHOULD use that
information as a hint in assigning IPv6 address(es)/prefix(es) to the
client.
DHCPv6 servers unaware of the RALS Option will ignore the option upon
reception .
There is no requirement that a server return this option and its data
in a RELAY-REPLY message.
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6. Security Considerations
The RALS Option allows a relay agent to specify the link/subnet on
which to allocate IPv6 address/prefix for a DHCPv6 client. The
existence of the RALS Option documented here would allow a malicious
DHCPv6 client to perform a more complete address-pool exhaustion
attack than could be performed without the use of this, since the
client would no longer be restricted to attacking address-pools on
just its local subnet.
The DHCPv6 RALS Option depends on a trusted relationship between the
DHCPv6 relay agent and the server. If a client message is relayed
through multiple relay agents, each of the relay agents must have
established independent, pairwise trust relationships. While the
introduction of fraudulent RALS may be prevented by a perimeter
defense that blocks these options unless the relay agent is trusted,
a deeper defense using IPsec[RFC2401] between the relay agent(s) and
the server SHOULD be deployed as well. Refer to Section 21.1 of
[RFC3315] for detail IPsec configurations required to protect
communications between the DHCPv6 relay agent(s) and server.
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7. IANA Considerations
IANA is requested to assign a DHCPv6 option code for the RALS Option.
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8. Acknowledgements
Thanks Spencer Dawkins for providing his valuable advices for this
document.
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9. References
9.1. Normative References
[I-D.giaretta-netlmm-dt]
Giaretta, G., Leung, L., and M. Liebsch, "NetLMM
Protocol", draft-giaretta-netlmm-dt-protocol-00 (work in
progress), June 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
9.2. Informative References
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, Nov. 1998.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
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Author's Address
Yuping Zhao(Amy Zhao)
Huawei Technologies Co.,Ltd
Huihong Mansion,No.91 Baixia Rd.
Nanjing, Jiangsu 210001
P.R.China
Phone: +86(25)84565403
Email: zhaoyuping@huawei.com
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