IETF Mobile IPv6 Working Group Hee Jin Jang
Internet-Draft Alper Yegin
Expires: November 25, 2004 JinHyeock Choi
SAMSUNG AIT
May 31, 2004
DHCP Option for Home Agent Discovery in MIPv6
draft-jang-dhc-haopt-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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This Internet-Draft will expire on November 25, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This draft defines a DHCP-based scheme to enable dynamic discovery of
Mobile IPv6 home agent address and home subnet. A new DHCP option is
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 Agent Discovery Option . . . . . . . . . . . . . . . . . 5
3.2 Mobile Node Identifier Sub-option . . . . . . . . . . . . . . 5
3.3 Home Network Information Sub-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 . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 11
Normative References . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12
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 dynamic home agent
discovery using the prefix information. In addition to delivering the
prefix information, DHCP can also be used to directly provide the IP
addresses of the home agents that are available to the mobile node.
The solution involves defining a new DHCP option to carry home agent
IP address and home subnet prefix information. A similar solution has
already been defined for Mobile IPv4 home agents[6].
As part of configuring the initial TCP/IP parameters, a mobile node
can obtain home agent information for the subnet it is directly
attached to, other subnets in the visited domain, or a subnet from
its home domain. Mobile node can provide its identity in order to
make the selection. For example the mobile node can provide its FQDN
or its user's NAI and expect that a home agent 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.
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 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[5].
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3. DHCP options for HA Dynamic Discovery
This section introduces DHCP options used for dynamic home agent
discovery in Mobile IPv6.
3.1 Home Agent Discovery Option
This is a new DHCP option for the dynamic home agent discovery. It
acts as a container for the following sub-options: Mobile Node
Identifier (MNId) and Home Network Information (HNInf) sub-options.
The mobile node MUST include MNId sub-option along with its Option
Request option in its request. If the DHCP server identifies any
matching home agent address or home subnet prefix, it MUST deliver
them via HNInf sub-option(s).
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_HADISCOVER | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. Sub-options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code
OPTION_HADISCOVER (TBD).
option-len
Total length of the sub-options.
3.2 Mobile Node Identifier Sub-option
Mobile node uses this sub-option to identify itself to the DHCP
server. DHCP server uses this identification to determine the
matching home agent and home subnet information. 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. The specifics of these mechanisms are
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outside the scope of this draft.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subopt-type | subopt-len | id-type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
. .
. Mobile Node Identifier .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
subopt-type
MNId_SUBOPT (TBD)
subopt-len
Length of the Mobile Node Identifier field plus 1.
id-type
The type of Mobile Node Identifier. Possible values are:
0 Any mobile node from the local domain
1 NAI
2 FQDN
3 Opaque
o Type 0 indicates that the mobile node wants to discover the home
agents and home subnets within the local domain where it is currently
attached to. The length of the identifier field MUST be set to 0.
o Type 1 and Type 2 indicate that the mobile node wants to learn the
home agents and home subnets that match its NAI [3] [4] or FQDN,
respectively. The Mobile Node Identifier field MUST be set to the NAI
or FQDN of the mobile node.
o Type 3 means the mobile node identifier does not have any specific
format. Use of this type is application-specific.
3.3 Home Network Information Sub-option
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This is a sub-option is used to carry one or more home subnet
prefix(es) and home agent address(es) to a mobile node. The option
can carry a mix of home addresses and home subnet prefixes at the
same time.
The server MUST provide all of the matching home agent address(es)
and home subnet prefix(es) in a HNinf Sub-option. If the server has
no information to provide, it MUST reply with the Home Agent
Discovery option and set its option-len field to zero.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| subopt-type | subopt-len |A| reserved | prefix length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ home agent address or prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
subopt-type
HNInf_SUBOPT (TBD)
subopt-len
18
home agent address flag (A)
1-bit home agent address flag. When set, it indicates
that the following data field contains the complete IPv6
address of a home agent.
When the flag is set to zero, it indicates that the
following data field contains only a home subnet prefix
that the mobile node may use for the dynamic home agent
address discovery mechanism as described in Section
11.4.1 of Mobile IPv6[1].
reserved
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This field is currently unused and reserved for future use.
It MUST be initialized to zero by the sender and MUST
be ignored by the receiver.
prefix length
8-bit unsigned integer. The number of leading bits
of the following 128-bit value that are valid as
a home subnet prefix. The value ranges from 0 to 128.
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4. Option Usage
The requesting and sending of this option follows the rules for DHCP
options in [5].
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 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 Agent information at the same time.
A mobile node MUST identify itself with Mobile Node Identifier
Sub-option to facilitate a DHCP server to provide the matching
information. For example, a DHCP server may have information about
home agents from several domains (and subnets). It relies on the
mobile node identifier 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.
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
the mobile node identifier, it returns a Home Agent Discovery Option
with 0-length data.
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5. Security Considerations
Secure delivery of home agent 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. DHCP authentication mechanism
MUST be used when the operator seeks authentication of the requestor
and the information source (DHCP server). In that case, the Mobile
Node Identifier MUST be compatible with the DHCP client identifier.
For example, if the Mobile Node Identifier type is 0, the DHCP client
identifier MUST belong to the local domain.
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 one new DHCPv6 option, Home Agent Discovery
option which has two sub-options, Mobile Node Identifier and Home
Network Information. The type numbers for new DHCP option and
sub-options are currently TBD. An appropriate request will be made to
IANA if this Internet draft gets accepted as an RFC.
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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", draft-ietf-mobileip-ipv6-24 (work in progress), July
2003.
[3] Aboba, B. and M. Beadles, "The Network Access Identifier", RFC
2486, January 1999.
[4] Calhoun, P. and C. Perkins, "Mobile IP Network Access Identifier
Extension for IPv4", RFC 2794, March 2000.
[5] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003.
[6] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[7] Soliman, H., Castelluccia, C., Malki, K. and L. Bellier,
"Hierarchical Mobile IPv6 mobility management (HMIPv6)",
draft-ietf-mipshop-hmipv6-01 (work in progress), February 2004.
[8] Levkowetz, H., "DHCP Option for Mobile IP Mobility Agents",
draft-ietf-dhc-mipadvert-opt-02 (work in progress), February
2004.
Authors' Addresses
Hee Jin Jang
i-Networking Lab Samsung AIT
P.O. Box 111 Suwon
440-600 Korea
EMail: heejin.jang@samsung.com
Alper E. Yegin
i-Networking Lab Samsung AIT
75 West Plumeria Drive
San Jose, CA 95134 USA
EMail: alper.yegin@samsung.com
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JinHyeok Choi
i-Networking Lab Samsung AIT
P.O. Box 111 Suwon
440-600 Korea
EMail: athene@sait.samsung.co.kr
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Acknowledgement
Thank Youn-Hee Han, Jung-Hoon Cheon and Xiaoyu Liu who discussed
together and gave the helpful advice on this draft.
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