MIP6 Working Group Hee Jin Jang
Internet-Draft Alper Yegin
Expires: December 10, 2006 JinHyeock Choi
SAMSUNG AIT
Kuntal Chowdhury
Starent Networks
June 8, 2006
DHCP Option for Home Information Discovery in MIPv6
draft-jang-mip6-hiopt-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This draft defines a DHCP-based scheme to enable dynamic discovery of
Mobile IPv6 home agent address, home address, and home subnet. New
DHCP options are defined to carry the information from a DHCP server
to the DHCP client running on the mobile node.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. DHCP options for HA Dynamic Discovery . . . . . . . . . . . . 5
3.1. Home Network Identifier Option . . . . . . . . . . . . . . 5
3.2. Home Network Information Option . . . . . . . . . . . . . 6
4. Option Usage . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. DHCP Server - Home Agent Relation . . . . . . . . . . . . 9
4.2. Mobile Node Considerations . . . . . . . . . . . . . . . . 9
4.3. DHCP Server Considerations . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 12
7. Normative References . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
Before a mobile node can engage in Mobile IPv6 signaling with a home
agent, it should either know the IP address of the home agent via
preconfiguration, or dynamically discover it. Mobile IPv6
specification [2] describes how home agents can be dynamically
discovered by mobile nodes that know the home subnet prefix. This
scheme does not work when prefix information is not already available
to the mobile node. This problem can be solved by delivering one or
more home subnet prefix information to the mobile node by means of
DHCP. Subsequently, the mobile node can engage in dynamic home agent
discovery using the prefix information. In addition to delivering
the prefix information, DHCP can also be used to provide the IP
addresses or FQDNs of the home agents that are available to the
mobile node and the home address that the mobile node can use to
register with the home agent.
The solution involves defining new DHCP options to carry home subnet
prefix, home agent IP address, home agent's FQDN information, and
home address of the mobile node. A similar solution has already been
defined for Mobile IPv4 home agents [3].
As part of configuring the initial TCP/IP parameters, a mobile node
can obtain home network information for the subnet it is directly
attached to, other subnets in the visited domain, or a subnet from
its home domain. A mobile node can convey the target home subnet's
identity in order to receive corresponding information. For example
the mobile node can provide realm portion of its user NAI (Network
Access Identifier) and expect that a home network information from
its home domain is returned. The availability of the requested
information depends on the DHCP server having prior knowledge or
dynamically discovering it. While the specific details are outside
the scope of this document, use of static tables and AAA-assisted
discovery are possible options [8].
The mobile node may or may not be connected to the "home" subnet when
it attempts to learn Mobile IPv6 home network information. This
allows operators to centrally deploy home agents while being able to
bootstrap mobile nodes that are already roaming. This scenario also
occurs when HMIP [7] is used, where the mobile node is required to
discover the MAP (a special home agent) that is located multiple hops
away from the mobile node's attachment point.
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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 [1].
Most of terms used in this draft are defined in Mobile IPv6 [2] and
RFC3315 [4].
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3. DHCP options for HA Dynamic Discovery
This section introduces two DHCP options used for dynamic home agent
discovery in Mobile IPv6.
3.1. Home Network Identifier Option
This option is used to carry the identifier of the target home
network. This identification allows mobile node to request
information for a home subnet within the visited domain, or from a
specific domain. It is assumed that the DHCP server has some
mechanism to know or retrieve the requested Mobile IPv6 information
such as [9]. The specifics of these mechanisms are outside the scope
of this draft.
The mobile node MUST include this option along with its Option
Request option in its request.
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_HNId | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| id-type |A| reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Home Network Identifier .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code
OPTION_HNId (TBD)
option-len
Total length of the option
id-type
The type of Home Network Identifier:
0 Local (visited) domain
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1 Network realm
A flag
A flag to specify whether the client requests a home
address or not.
reserved
8-bit field reserved for future use. The value MUST be
initialized to zero by the sender, and MUST be ignored
by the receiver.
Id-type 0 indicates the mobile node is interested in learning the
home network information that pertains to the immediately connected
(visited) network. In that case, Home Network Identifier field is
not used. This type can be used to discover local home agents in a
visited network.
Id-type 1 indicates the format of Home Network Identifier field is a
network realm as defined in [5]. In this case, the mobile node is
interested in learning home network information that pertains to the
given realm. This type can be used to discover home agents that are
hosted by a user's home domain (as indicated by his/her NAI-based
username -- user@HomeRealm).
If A flag is set in this option, the server should assign a home
address to the client in the returned Home Network Information
option. Otherwise, the server should not assign a home address
option.
3.2. Home Network Information Option
This option is used to carry home network information to a mobile
node in the form of one or more of home subnet prefix(es), home agent
address(es), home agent FQDN(s), and mobile node's home address.
The server MUST provide all of the matching home subnet prefix(es),
home agent address(es) or FQDN(s) in a Home Network Information
option. If the server has no information to provide, it MUST set the
option-len field to zero in this option. If the client set the A
flag in Home Network Identifier option, it MUST provide an available
home address to a client.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_HNInf | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| hninfo-type | hninfo-len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Home Network Information .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code
OPTION_HNInf (TBD)
option-len
Total length of the option
hninfo-type
The type of following Home Network Information field.
Possible values are:
0 Home subnet prefix
1 Complete IPv6 address of the home agent
2 FQDN of the home agent
3 IPv6 Home address
hninfo-len
8-bit unsigned integer. Total length of the following
Home Network Information field.
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Home Network Information
A home subnet prefix, home agent IP address, FQDN
and home address to be assigned to a mobile node.
When hninfo-type is set to 0, the data field MUST
contain 8-bit prefix length information followed
by a 128-bit IPv6 address beginning with the
available network prefix.
When hninfo-type is set to 1, the data field MUST
contain a 128-bit IPv6 address of the home agent.
When hninfo-type is set to 2, the data field MUST
contain a FQDN as described in RFC1035 [6].
When hninfo-type is set to 3, the data field MUST
contain the 8-bit reserved field, 8-bit prefix length
field of the following home address, 32-bit lifetime
of the following home address and the 128-bit home
address to be assigned to a client. The lifetime is
expressed in units of seconds.
The home address, or hninfo-type = 3, should be included if and only
if the client sets A flag in Home Network Identifier option. Setting
the lifetime to 0xffffffff ("infinity") means a permanent assignment
of an address to the client. The lifetime of the assigned home
address should not be longer than the lifetime of its prefix since
the home address cannot survive the prefix lifetime.
If id-type is 0 in Home Network Identifier option, the server should
reply with the available home agent(es) or home address information
in the visited network. Otherwise, it should return that information
in the specified home network in Home Network Identifier field in the
request option.
Single option can carry multiple information preceded by hninfo-type
and hninfo-len fields. The length fields help identify the
information boundaries.
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4. Option Usage
The requesting and sending of this option follows the rules for DHCP
options in [4].
4.1. DHCP Server - Home Agent Relation
The DHCP server does not have to be co-located with a home agent, or
even be on the home subnet of the mobile node. Its location with
respect to home network does not matter as long as it possesses the
requested information.
4.2. Mobile Node Considerations
When a Mobile IPv6 mobile node finds itself with neither a home
subnet prefix/home address nor a home agent address, it may request
the needed information with Option Request option. For instance, a
mobile node connecting to a network for the first time may acquire a
DHCP address and solicit for home network information at the same
time.
A mobile node MUST identify the desired information with Home Network
Identifier option. For example, a DHCP server may have information
about home agents from several domains (and subnets). It relies on
the mobile node to select the domain for determining which ones it
should provide in response to the client's request.
When the mobile node gets more than one home agent address, it MUST
have a selection mechanism to determine which one to use for
establishing a Mobile IPv6 session. In case it retrieves only home
subnet prefix(es), it needs to perform dynamic home agent discovery
to learn the IP addresses of the home agents. Similarly, if FQDN of
a home agent is retrieved, the mobile node can use DNS to resolve it
to IPv6 address(es) of the home agents. If the mobile node receives
both IPv6 address(es) and FQDN(s) of the home agents, it SHALL use
the IPv6 information of the home agents. When the mobile node
requests and receives the home address information from the DHCP
server, it SHALL use it to perform Mobile IPv6 home registration.
For detailed mobile node behavior, refer to section 3.6 of [9].
When an MN sends a Binding Update message to home agent by using HoA
which is assigned in Home Network Information option, the requested
lifetime in Binding Update message MUST not be shorter than the
lifetime of the HoA. Since the HoA lifetime is not greater than its
prefix lifetime, it is guaranteed that binding cache entry's lifetime
is not greater than the home prefix lifetime. Note that, according
to 10.3.1 of MIPv6, the lifetime for the binding cache entry MUST NOT
be greater than the remaining valid lifetime for the subnet prefix of
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HoA specified with the Binding Update.
4.3. DHCP Server Considerations
It is assumed that the DHCP server has access to home network
information for its clients for this option to be useful. The DHCP
server can rely on pre-configuration, or some dynamic discovery
mechanisms for obtaining this information. In case it does not have
any information, or it cannot locate matching information based on
Home Network Identifier, it returns a Home Network Information option
with 0-length data. The DHCP server can either return the IPv6
address(es) of home agent or the FQDN(s) of home agents. It is not
required for the DHCP server to return both.
When a DHCP server assigns a HoA to an MN, it should guarantee that
the lifetime of assigned HoA MUST NOT be greater than that of the
subnet prefix in the MN's HoA. The lifetimes of HoAs for assignments
are can be negotiated when the home prefix is delivered from the home
agent, or configured by DHCP administrator's policy. The details are
outside the scope of this document.
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5. Security Considerations
Secure delivery of home agent, home address, and home link
information from a DHCP server to the mobile node (DHCP client)
relies on the overall DHCP security. The particular option defined
in this draft does not have additional impact on the DHCP security.
Aside from the DHCP client to server interaction, an operator must
also ensure secure delivery of mobile IP information to the DHCP
server. This is outside the scope of DHCP and the newly defined
option.
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6. IANA Consideration
This document introduces two new DHCPv6 options, Home Agent Request
option and Home Agent Reply option. The type numbers for new DHCP
options are currently TBD. An appropriate request will be made to
IANA if this Internet draft gets accepted as an RFC.
7. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[3] Levkowetz, H., "DHCP Option for Mobile IP Mobility Agents",
draft-ietf-dhc-mipadvert-opt-02 (work in progress),
February 2004.
[4] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003.
[5] Aboba, B. and M. Beadles, "The Network Access Identifier",
RFC 2486, January 1999.
[6] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[7] Soliman, H., Castelluccia, C., Malki, K., and L. Bellier,
"Hierarchical Mobile IPv6 mobility management (HMIPv6)",
draft-ietf-mipshop-hmipv6-04 (work in progress), December 2004.
[8] Chowdhury, K. and A. Lior, "RADIUS Attributes for Mobile IPv6
bootstrapping", draft-chowdhury-mip6-bootstrap-radius-01 (work
in progress), November 2004.
[9] Chowdhury, K. and A. Yegin, "MIP6-bootstrapping via DHCPv6 for
the Integrated Scenario",
draft-ietf-mip6-bootstrapping-integrated-dhc-00 (work in
progress), October 2005.
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Authors' Addresses
Hee Jin Jang
Samsung Advanced Institute of Technology
P.O. Box 111
Suwon 440-600
Korea
Email: heejin.jang@samsung.com
Alper E. Yegin
Samsung Advanced Institute of Technology
Istanbul
Turkey
Email: alper01.yegin@partner.samsung.com
JinHyeok Choi
Samsung Advanced Institute of Technology
P.O. Box 111
Suwon 440-600
Korea
Email: athene@sait.samsung.co.kr
Kuntal Chowdhury
Starent Networks
30 International Place
Tewksbury, MA 01876
US
Email: kchowdhury@starentnetworks.com
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