Mobile IP Working Group Milind Kulkarni
INTERNET-DRAFT Alpesh Patel
Category: Standards Track Kent Leung
Date : 28 April 2004 Cisco Systems Inc.
Mobile IPv4 Dynamic Home Agent Assignment
draft-ietf-mip4-dynamic-assignment-01.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet
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Abstract
Mobile IP (RFC 3344) uses the Home Agent (HA) to anchor
sessions of a roaming Mobile Node (MN). This draft proposes a
messaging mechanism for dynamic home agent assignment and HA
redirection. The goal is to provide a mechanism to assign an
optimal HA for a Mobile IP session while allowing any suitable
method for HA selection.
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Table of Contents
1. Introduction.....................................................2
2. Terminology.......................................................3
3. Problem Statement.................................................4
3.1 Scope............................................................5
3.2 Dynamic Home Agent Discovery in RFC 3344.........................5
3.3 NAI usage and dynamic HA assignment..............................5
3.4 Dynamic HA extension.............................................5
3.4.1 Redirected HA extension........................................6
3.4.2 Requested HA extension.........................................6
4. Messaging mechanism for dynamic HA assignment/redirection.........7
4.1 Messaging for dynamic HA assignment..............................7
4.1.1 Example with Message Flow Diagram..............................7
4.2 Messaging for HA redirection.....................................9
4.2.1 Example with Message Flow Diagram.............................10
5. Mobility Agent Considerations for dynamic HA assignment..........11
5.1 Mobile Node Considerations......................................11
5.1.1 MN using FA CoA...............................................12
5.1.2 MN using Collocated CoA.......................................12
5.1.3 Refreshing Assigned HA Address on Mobile Node.................13
5.2 Foreign Agent Considerations....................................13
5.3 Home Agent Considerations.......................................13
5.3.1 Assigned Home Agent Considerations............................14
6. Requested Home Agent Selection...................................16
7. Error Values.....................................................17
8. IANA Considerations..............................................17
9. Security Considerations..........................................17
9.1 Message Authentication Codes....................................17
9.2 Areas of Security Concern in this Protocol......................18
10. Backward Compatibility Considerations...........................18
11. Change Log from previous version................................19
12. Intellectual Property Rights....................................19
13. Acknowledgements................................................19
14. References......................................................19
Authors' Addresses..................................................20
Full Copyright Statement............................................20
Intellectual Property...............................................21
Acknowledgement.....................................................21
1. Introduction
This document adds to the Mobile IP protocol [1], by proposing
a messaging mechanism for dynamic home agent assignment and
home agent redirection during initial registration. The goal is
to assign an optimal HA for a Mobile IP session. The mobile
node MUST use Network Access Identifier (NAI) extension for
home address assignment.
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MN requests the network to dynamically assign an HA by setting
HA field to ALL-ZERO-ONE-ADDR (defined in next section) in
initial Registration Request. If the request is accepted, the
HA field in successful Registration Reply contains the HA
address. The requested HA can suggest an alternate HA and if
so, the Registration Reply is rejected with a new error code
(REDIRECT-HA-REQ) and the alternate HA address is specified in
a new extension (Redirected HA extension).
If the RRQ is rejected with Redirected HA extension or if the
MN wishes to register at a specific HA, MN can put the HA
address in the Requested HA extension in Registration Request.
The HA address in Requested HA extension is a hint to the
network where the MN may be anchored. The HA field is set to
ALL-ZERO-ONE-ADDRESS for dynamic HA assignment.
The messaging mechanism proposed here is generic and can be
used as a common foundation to facilitate dynamic HA assignment
using any suitable method. No specific method is either
mandated or suggested. The HA receiving Registration Request
may suggest an alternate HA (HA redirection) for a number of
reasons; including but not limited to HA load-balancing,
geographical proximity, administrative policy etc.
2. Terminology
ALL-ZERO-ONE-ADDR: IP address 0.0.0.0 or 255.255.255.255. An
address of 255.255.255.255 would indicate
assigning HA in home domain. An address of
0.0.0.0 would mean MN just needs a dynamic
HA, it does not care whether in home or
visited domain.
Requested HA: Destination IP address of Home Agent that the
first Registration Request is sent to. Must
be a unicast IP address. This address can be
obtained as described in section 5.4.
Assigned HA: If registration is successful, this Home
Agent address field is obtained from
successful Registration Reply.
Redirected HA: If the registration is rejected with error
code (REDIRECT-HA-REQ), the HA being referred
to is specified in a new extension
(Redirected HA extension).
AAA server: Authentication, Authorization and Accounting
Server.
DNS: Domain Name Service.
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DHCP: Dynamic Host Configuration Protocol.
MN: Mobile Node as defined in RFC 3344.
HA: Home Agent as defined in RFC 3344.
FA: Foreign Agent as defined in RFC 3344.
CoA: Care of Address.
CCoA: Collocated Care of Address.
MN HoA: Mobile Node's Home Address.
NAI: Network Access Identifier [2].
Src IP: Source IP address of the packet.
Dest IP: Destination IP address of the packet.
3. Problem Statement
Mobile IPv4 NAI Extension for IPv4 [2] introduced the concept
of identifying a MN by the NAI and enabling dynamic home
address assignment. When the home address is dynamically
assigned, it is desirable to discover the Home Agent
dynamically or inform the MN about an optimal HA to use for a
multitude of reasons, such as:
- If the distance between the visited network and the home
network of the mobile node is large, the signaling delay for
these registrations may be long. In such a case the MN will be
anchored to its distant home agent, resulting in tunneled
traffic traveling a long distance between home agent and the
mobile node. When a Mobile IP session initiates, if the mobile
node can be assigned a home agent, which is close to the mobile
node, it can drastically reduce the latency between the home
agent and mobile node.
- Also, in a large scale Mobile IP deployment, it is cumbersome
to provision MNs with multiple HA addresses.
- It is desirable to achieve some form of load balancing
between multiple HAs in the network. Dynamic HA assignment
and/or HA redirection lets the network select the optimal HA
from among a set of HAs and thus achieve load balancing among a
group of HAs.
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- Local administrative policies is yet another reason for
dynamic HA assignment/HA redirection during the start of a
Mobile IP session.
- The problem of discovering a Mobile nodes HA address is
acknowledged in the MIPv6 working group as part of [8].
3.1 Scope
This specification assumes that the Mobile Node and Assigned
Home Agent are in the same administrative domain. The scenario
where the Mobile Node and its anchoring Assigned Home Agent are
in different administrative domain is beyond the scope of this
specification.
The draft introduces the terms Requested/Assigned/Redirected HA
(section 5.4). These terms are merely HA addresses and used
depending upon the direction of the registration request or
reply. The discovery of Requested/Assigned/Redirected HA can be
done by various means, which are network and/or deployment
specific and hence this discovery/assignment of
Requested/Assigned/Redirected HA is kept outside the scope of
this specification.
3.2 Dynamic Home Agent Discovery in RFC 3344
Mobile IP RFC 3344 specifies the mechanism for discovering the
mobile node's home agent using subnet-directed broadcast IP
address in the home agent field of the Registration Request.
This mechanism was designed for mobile nodes with a static home
address and subnet prefix, anchored on fixed home network. But
using subnet-directed broadcast as the destination IP address
of the Registration Request, it is unlikely that the
Registration Request will reach the home subnet because routers
will drop these packets by default. See CERT Advisory CA-1998-
01 Smurf IP Denial-of-Service Attacks [3].
3.3 NAI usage and dynamic HA assignment
Mobile IPv4 NAI Extension for IPv4 [2] introduced the concept
of identifying a MN by the NAI and enabling dynamic home
address assignment. This document mandates that while using
dynamic HA assignment, MN MUST use NAI and obtain a home
address. MN can still suggest a static home address in
Registration Request, but must take the address in Registration
Reply as the home address for the session. This reference to
obtaining home address using NAI is as per [2].
3.4 Dynamic HA extension
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The Dynamic HA extension, shown in figure 1, contains the
address of the HA. This is a generic extension and can be used
in Registration Request and Reply messages. It is a skippable
extension.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Sub-Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HA-Address...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The Dynamic HA address Extension
Type DYNAMIC-HA-ADDRESS (skippable) [1] (to be
assigned by IANA) is the type, which specifies the
dynamic HA address.
Sub-Type is a unique number given to each member in the
aggregated type.
Length Indicates the length of the extension not including
the type, sub-type and length fields.
HA-Address The address of HA
3.4.1 Redirected HA extension
The format of the Redirected HA extension is as defined in
section 3.4. This extension uses the subtype value of 1. This
extension has the length field set to 4.
The Redirected HA extension, contains the address of the HA
where the MN should attempt the next registration. The HA
receiving a Registration Request can suggest an alternate HA
and if so, the Registration Reply is rejected with a new error
code (REDIRECT-HA-REQ) and the alternate HA address is
specified in this extension.
It MUST be included in Registration Reply when the reply code
is REDIRECT-HA-REQ.
3.4.2 Requested HA extension
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The format of the Requested HA address extension is as defined
in section 3.4. This extension uses the subtype value of 2.
This extension has the length field set to 4.
MN may include the Requested HA extension in the registration
request as a hint to the network where it wishes to be
anchored. This extension contains the address of the HA. A
valid unicast IP address MUST be used as HA address in this
extension.
In absence of an FA, the RRQ is forwarded to this HA. In
presence of an FA, FA MUST forward RRQ to the HA address in
this extension.
4. Messaging mechanism for dynamic HA assignment/redirection
4.1 Messaging for dynamic HA assignment
1. MN sets the Home Agent address field in the Registration
Request to ALL-ZERO-ONE-ADDR.
If the MN is aware of an HA address, it can add that
address in the Requested HA extension in Registration
Request.
2. The MN (if using collocated CoA) or FA (if using FA CoA)
sends the Registration Request to the "Requested HA".
If the Requested HA extension is present, Requested HA is
the HA address in this extension.
3. "Requested HA" is the home agent, which processes the
Registration Request in accordance with RFC 3344 and as
per the specification in this document. It creates
mobility binding for successful Registration Request. It
also sends Registration Reply to the MN.
4. The MN obtains an "Assigned HA" address from the HA field
in the successful Registration Reply and uses it for the
remainder of the session.
5. Subsequent Registration Request messages for renewal are
sent to the Assigned HA.
Section 5.3.1 describes the Assigned HA in detail. Some ideas
on how to select the Requested HA are briefly covered in
section 6.
4.1.1 Example with Message Flow Diagram
Detailed explanation of this specification is best described
with the help of a railroad diagram and description.
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Figure 2 shows one specific example of a Mobile Node using FA
Care of Address.
Other scenarios such as mobile node using collocated care of
address are not described below, but the behavior is similar.
MN FA Requested/Assigned HA
| 1 | |
|------------>| 2 |
| |--------------->|
| | |
| | |
| | 3 |
| 4 |<---------------|
|<------------| |
| | |
| | 5 |
|----------------------------->|
| | |
Figure 2: Example of Message flows for the specification
1. MN sets the Home Agent address field in the Registration
Request to ALL-ZERO-ONE-ADDR. Since MN is using FA CoA in this
example, it sends the Registration Request to the FA. The
Registration Request looks as follows:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| MN | FA | | ALL-ZERO-ONE-ADDR |FA CoA |
+-----------------------------------------------------------+
If the MN is aware of an HA address, it can add that address in
the Requested HA extension in Registration Request. That
extension is not shown above.
2. The FA sends the Registration Request to the Requested HA.
The Registration Request looks as follows:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| FA |Requested HA| | ALL-ZERO-ONE-ADDR |FA CoA |
+-----------------------------------------------------------+
If MN had included the Requested HA extension, the Registration
Request is sent to the HA address in that extension.
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3. HA processes the Registration Request in accordance with RFC
3344 and the messaging defined in this document. HA creates
mobility binding for successful request. HA then sends
Registration Reply to the FA, which looks as follows. The
Assigned HA address corresponds to the HA receiving and
processing the request (and is same as Requested HA, only the
name is changed for registration reply).
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
|Assigned|CoA or NATed| | Assigned HA |FA CoA/|
| HA | Src IP | | | |
+-----------------------------------------------------------+
4. The FA relays the Registration Reply to the MN, as follows.
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| FA | MN | | Assigned HA |FA CoA/|
+-----------------------------------------------------------+
5. The MN obtains Assigned HA address from the HA field in the
successful Registration Reply and uses it for the remainder of
the session. MN sends subsequent Re-Registration or De-
Registration Requests for the remaining session directly to the
Assigned HA.
4.2 Messaging for HA redirection
1. MN sets the Home Agent address field in the Registration
Request to ALL-ZERO-ONE-ADDR.
2. The MN (if using collocated CoA) or FA (if using FA CoA)
sends the Registration Request to the "Requested HA". If
the MN is aware of an HA address, it can add that address
in the Requested HA extension in Registration Request.
3. When HA receives the Registration Request, if the HA field
is set to ALL-ZERO-ONE-ADDR, HA may reject the request
with Reply code REDIRECT-HA-REQ and suggest an alternate
HA.
HA may reject the Request for a number of reasons, which
are outside the scope of this specification. If the HA
rejects the Request, the HA field in the Reply is set to
this HAs address. The HA that is being referred to is
specified in Redirected HA extension. The presence of this
extension is mandatory when the reply code is set to
REDIRECT-HA-REQ. HA sends the Reply to the FA/MN
4. FA sends the Reply to the MN.
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5. If the error code is set to REDIRECT-HA-REQ, MN obtains
the HA address from Redirected HA extension and sends a
Registration Request to this HA.
4.2.1 Example with Message Flow Diagram
Figure 3 shows one specific example of a Mobile Node using FA
Care of Address.
MN FA Requested HA Redirected HA
| 1 | | |
|------------>| 2 | |
| |--------------->| |
| | | |
| | | |
| | 3 | |
| 4 |<---------------| |
|<------------| | |
| | | |
| | 5 | |
|-------------------------------------------------> |
| | | |
Figure 3: Example of Message flows for the specification
1. MN sets the Home Agent address field in the Registration
Request to ALL-ZERO-ONE-ADDR address. Since MN is using FA CoA
in this example, it sends the Registration Request to the FA.
The Registration Request looks as follows:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| MN | FA | | ALL-ZERO-ONE-ADDR |FA CoA |
+-----------------------------------------------------------+
If the MN is aware of an HA address, it can add that address in
the Requested HA extension in Registration Request. That
extension is not shown above.
2. The FA sends the Registration Request to the Requested HA.
If Requested HA extension is present, Requested HA is the HA
address in this extension. The Registration Request looks as
follows:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| FA |Requested HA| | ALL-ZERO-ONE-ADDR |FA CoA |
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+-----------------------------------------------------------+
3. HA processes the Registration Request in accordance with RFC
3344 and the messaging defined in this document. If the
registration is successful, but local configuration/
administrative policy etc. directs HA to refer the MN to
another HA, HA rejects the Request with error code REDIRECT-HA-
REQ. HA fills in the address of the directed HA in the
Redirected HA extension. HA then sends Registration Reply
reject to the FA, which looks as follows:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| |CoA or NATed| | HA |FA CoA |
| HA | Src IP | | | |
+-----------------------------------------------------------+
| Redirected HA extension ...
+-----------------------------------------------------------+
4. The FA relays the Registration Reply to the MN, as follows.
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| FA | MN | | HA |FA CoA/|
+-----------------------------------------------------------+
| Redirected HA extension ...
+-----------------------------------------------------------+
5. If MN can authenticate the Reply, MN extracts the HA address
from Redirected HA extension and sends Registration Request to
this HA.
5. Mobility Agent Considerations for dynamic HA assignment
Following sections describe the behavior of each mobility agent
in detail.
5.1 Mobile Node Considerations
The mobile node MUST use NAI extension for home address
assignment when using the messaging mechanism in this document.
While dynamic HA assignment is in progress and MN has not
successfully anchored at a Home Agent, mobile node MUST set the
Home Agent field in the Registration Request to an ALL-ZERO-
ONE-ADDR, which is either 255.255.255.255 or 0.0.0.0.
The Registration Request MUST be protected by a valid
authenticator as specified in [1] or [5]. Configuring security
associations is deployment specific and hence outside the scope
of this specification. The security associations between a MN
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and an individual HA may also be dynamically derived during the
dynamic HA assignment, based on a shared secret between MN and
AAA infrastructure.
The mobile node must maintain the remaining Mobile IP session
with the Assigned HA. Following sections describe MN behavior
in FA CoA mode and collocated CoA mode.
5.1.1 MN using FA CoA
When a mobile node initiates Mobile IP session requesting
dynamic HA assignment, it MUST set the home agent address field
in the Registration Request to ALL-ZERO-ONE-ADDR. The
destination IP address of Registration Request is the FA. The
FA will determine the Requested HA and forward the Registration
Request to the Requested HA. Registration Request processing
takes place on the Requested HA as per the specification in
this draft.
The Registration Request MUST be appropriately authenticated
for the HA to validate the Request.
If successful Registration Reply is received, MN obtains
Assigned HA from the HA field of Reply.
If Registration Reply is received with code REDIRECT-HA-REQ, MN
MUST authenticate the Reply based on HA address in HA field of
Reply and attempt Registration with the HA address specified in
the Redirected HA extension. In some cases, MN may want to hint
to the network to be anchored at a specific HA. In both these
cases, MN MUST put the HA address in the Requested HA extension
in Registration Request.
5.1.2 MN using Collocated CoA
Mobile Node in collocated CoA mode requesting dynamic HA
assignment MUST set the home agent address field in the
Registration Request to ALL-ZERO-ONE-ADDR. The destination IP
address of the Registration Request is the Requested HA. Some
ideas to select a Requested HA are briefly covered in section
6.
If successful Reply is received, the MN obtains Assigned HA
address from successful Registration Reply. The MN MUST cache
the Assigned HA address for the length of the Mobile IP
session. The mobile node then MUST use this previously cached
Assigned HA address as the home agent address in subsequent re-
registration and de-registration request(s). This will make
sure that the mobile node will always be anchored to the
assigned home agent with which it was initially registered.
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If Registration Reply is received with code REDIRECT-HA-REQ, MN
MUST authenticate the Reply based on HA address in HA field of
Reply and attempt Registration with the HA address specified in
the Redirected HA extension. In some cases, MN may want to hint
to the network to be anchored at a specific HA. In both these
cases, MN MUST put the HA address in the Requested HA extension
in Registration Request.
While requesting dynamic HA assignment in collocated CoA mode,
Requested HA extension must always be included.
5.1.3 Refreshing Assigned HA Address on Mobile Node
When the Mobile IP session terminates, the mobile node MAY
clear the Assigned HA address cached as the home agent address.
It MAY request a new HA address for the new Mobile IP session
by not including the Requested HA extension. The advantage of
this approach is that the mobile node will be always anchored
to an optimal home agent from where it initiated Mobile IP
session.
Alternately, MN may save the Assigned HA address and use it in
the Requested HA extension along with ALL-ZERO-ONE HA address
in Registration Request.
5.2 Foreign Agent Considerations
When the mobile node is using foreign agent CoA, it sends the
Registration Request to the foreign agent. When the FA receives
a Registration Request with HA address field set to ALL-ZERO-
ONE-ADDR, it obtains the Requested HA address to forward the
Registration Request. Some ideas to select a Requested HA are
briefly covered in section 6.
If the FA cannot obtain the Requested HA to forward a
Registration Request from MN, it MUST reject request with error
code NONZERO-HA-REQD.
If the MN has included the Requested HA extension, FA MUST
forward Registration Request to the address in this extension.
If the HA address in this extension is not a routable unicast
address, FA MUST reject request with error code NONZERO-HA-
REQD.
Backward compatibility issues related to the mobility agents
are addressed in section 9.
5.3 Home Agent Considerations
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Home Agent can process an incoming Registration Request in one
of the following three ways:
MN or FA sends the Registration Request to the Requested HA.
The term Requested HA has meaning in context of the
Registration Request message. When the Requested HA
successfully processes Registration Request and creates a
binding and sends a Reply with its address, it becomes the
Assigned HA. The term Assigned HA is meaningful in context of a
Registration Reply message.
Home Agent receiving the request with HA field set to ALL-ZERO-
ONE-ADDR MAY reject the request even if successfully
authenticated for a multitude of reasons and suggest an
alternate HA address in Reply. In such a case, the HA puts its
own address in HA field of Reply and sets the Reply code to
REDIRECT-HA-REQ and adds the Redirected HA extension.
If the Registration Request contains the Requested HA
extension, the HA address in that extension must match the
destination IP of the Request.
5.3.1 Assigned Home Agent Considerations
The HA that processes the incoming Registration Request fully
in accordance with RFC 3344 and this specification becomes the
Assigned HA. The Registration Request terminates at the
Assigned HA.
The Assigned HA creates mobility bindings and sends
Registration Reply to the MN by copying its address in the home
agent field and as the source IP address of the Reply.
There are two IP addresses to consider, destination IP address
and Home Agent address field in the Registration Request. When
destination IP address is unicast, only one HA receives the
Registration Request. This HA should unambiguously accept or
deny the registration, regardless of the value in the Home
Agent field. When the Home Agent field is non-unicast, the HA
should set the value to its own IP address in the Registration
Reply.
The following table summarizes the behavior of Assigned HA.
No. Dest IP Addr HA field Processing at Assigned HA
-- ------------ ------------ -------------------------------
1 Unicast non-unicast RFC 3344: HA denies the
registration with error code
136 and sets HA field to its
own IP address in the reply as
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per section 3.8.3.2.
ALL-ZERO- New Behavior: Accept the RRQ as
ONE-ADDR per this specification.
Authenticate the RRQ and create
mobility binding if the HA is
acting as Assigned HA. Set HA
field to its own IP address in
the Registration Reply.
OR
New Behavior: Dest IP
corresponds to the HA receiving
RRQ, if authentication is
successful, reject RRQ with a
new error code (REDIRECT-HA-
REQ). HA puts its address in HA
address field of Reject. HA
suggests an alternate HA to use
in the new Redirected HA
extension
Table 1: Registration Request handling at Assigned HA
This specification also proposes a subtle difference in
behavior for case #1 above from RFC 3344. As per the messaging
proposed here, the mobile node (or the foreign agent) sends the
Registration Request to the Requested HA address, which is a
unicast address. Because HA does not receive Registration
Request that is sent to the subnet-directed broadcast address,
RFC 3344 section 3.8.2.1 doesn't apply. Although the Home
Agent field in the Registration Request is not a unicast
address, the destination IP address is a unicast address. This
avoids the problem associated with subnet-directed broadcast
destination IP address that may result in multiple HAs
responding. Thus, there is no need to deny the registration as
stated in RFC 3344 section 3.8.3.2.
When the destination IP address is a unicast address and Home
Agent field is ALL-ZERO-ONE-ADDR, the HA accepts/denies
registration and sets HA field to its own IP address in the
reply (i.e. registration is not rejected with error code 136).
HA can reject the request with the error code REDIRECT-HA-REQ
and suggest an alternate HA. This redirection can be used for
load-balancing, geographical proximity based on care-of-address
or a multitude of reasons. HA puts its own address in HA field
on Registration Reply message and put the address of the
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redirected HA in the Redirected HA extension. If HA accepts the
Request, HA field in Reply is set to this HA address.
The Assigned HA performs standard validity checks on the
Registration Request. If there is any error, the Registration
Request is rejected with error codes specified in RFC 3344.
6. Requested Home Agent Selection
The destination IP address of the Registration Request when
dynamic HA assignment is requested, is the Requested HA. This
address MUST be a unicast IP address. If the MN has included a
Requested HA extension in Registration Request, the HA address
in this extension is the Requested HA.
Some ideas on how to select the Requested HA are briefly
covered in this section, however this draft neither suggests
nor mandates any specific mechanism. There can be more methods
for selecting the HA to the MN. Here is a high level overview
of some possibilities:
DHCP:
MN performs DHCP to obtain an IP address on the visited
network. The Requested HA is learned from the DHCP Mobile IP
Home Agent Option 68 [4]. MN sends Registration Request
directly to this HA and receives the Assigned HA to be used for
the remainder of the Mobile IP session.
AAA:
MN performs challenge/response [5] with the FA. The FA
retrieves the Requested HA from the AAA server and forwards the
Registration Request directly to this HA. The Assigned HA
sends Registration Reply to the FA, which relays it to the MN.
MN uses the Assigned HA for the remainder of the Mobile IP
session.
DNS:
In this case hostname of HA is configured on MN or obtained by
some other means e.g. using a service location protocol. MN
performs DNS lookup on the HA hostname. The DNS infrastructure
provides resource record with information to identify the
nearest HA to the MN. The MN sends Registration Request
directly to the HA and receives the Assigned HA to be used for
remainder of the Mobile IP session.
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Static configuration:
HA address is statically configured on MN. The MN uses the
configured address to send the Registration Request.
7. Error Values
Each entry in the following table contains the name and value
for the error code to be returned in a Registration Reply. It
also includes the section in which the error code is first
mentioned in this document.
Error Name Value Section Description
---------- ----- ------- -----------------------------
NONZERO-HA-REQD XX 5.2 Non-zero HA address required
in Registration Request.
REDIRECT-HA-REQ YY 5.3.1 Reregister with redirected HA.
8. IANA Considerations
The code value NONZERO-HA-REQD defined in Section 7, correspond
to error values conventionally associated with the rejection by
the foreign agent (i.e. value in the range 64-127). The code
value REDIRECT-HA-REQ defined in Section 7, correspond to error
values conventionally associated with the rejection by the home
agent (i.e. value in the range 128-192).
The Dynamic HA extension defined in section 3.4 corresponds to
a skippable extension.
IANA should record the values as defined in Section 7 and 3.4.
9. Security Considerations
This specification assumes that the Mobile Node and Assigned
Home Agent are in the same administrative domain. This
specification does not change or degrade the security model
established in RFC-3344. Most of the time Mobile Nodes will be
connected to the network via wireless link. Such links are
vulnerable to passive eavesdropping, replay attacks or many
other types of attacks. They are considered below.
9.1 Message Authentication Codes
The Registration Request and Registration Reply messages are
protected by a valid authenticator as specified in RFC 3344.
Configuring security associations is a deployment specific
issue and is covered by other specifications in Mobile IP WG.
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There can be many ways of configuring security associations,
but this specification does not mandate any specific way.
An example is where the security association between a MN and
an individual HA (Dynamic or Assigned) is dynamically derived
during the dynamic HA assignment, based on a shared secret
between MN and AAA infrastructure, as defined in [7]. The
Registration Request is protected with MN-AAA authentication
extension and Registration Reply is protected with MHAE. Since
the security association is shared between MN and AAA, any
dynamically assigned HA in the local domain can proxy
authenticate the MN using AAA as per [7].
The Assigned Home Agent authenticates Registration Request from
the mobile node as specified in RFC-3344 and RFC-3012. The MN
also authenticates the Registration Reply from the Assigned HA,
thus the existing trust model in RFC 3344 is maintained.
9.2 Areas of Security Concern in this Protocol
As per the messaging in this draft, the Assigned Home Agent
will process the incoming Registration Request as per RFC-3344.
Hence the Assigned Home Agent will have same security concerns
as that of the Home Agent in RFC-3344. They are addressed in
Section 5 Security Considerations of RFC-3344.
10. Backward Compatibility Considerations
Legacy Home Agent:
Legacy home agents may reject the Registration Request with
error code 136 because the Home Agent field is not a unicast
address. However, some legacy HA implementations may
coincidentally process the Registration Request in accordance
with this draft, when the HA field in RRQ is set to ALL-ZERO-
ONE-ADDR.
Legacy Foreign Agent:
Legacy foreign agents may forward Registration Request with
home agent field set to ALL-ZERO-ONE-ADDR by setting the
destination IP address to ALL-ZERO-ONE-ADDR. This will result
packet being dropped or incidentally handled by a next hop HA,
adjacent to the FA.
Legacy Mobile Node:
MN that does not set HA field to ALL-ZERO-ONE-ADDR will
continue to achieve its registrations through statically
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configured HA. In collocated mode, the endpoint of the MN's
tunnel is the Assigned HA.
11. Change Log from previous version
1. Added subtype field in Redirected HA Address Extension.
2. Aligned the HA address at 4-byte world boundary.
3. The case of handling unicast HA field is removed in section
5.3.1.
12. Intellectual Property Rights
The IETF takes no position regarding the validity or scope of
any intellectual property or other rights that might be claimed
to pertain to the implementation or use of the technology
described in this document or the extent to which any license
under such rights might or might not be available; neither does
it represent that it has made any effort to identify any such
rights. Information on the IETF's procedures with respect to
rights in standards-track and standards-related documentation
can be found in BCP-11. Copies of claims of rights made
available for publication and any assurances of licenses to be
made available, or the result of an attempt made to obtain a
general license or permission for the use of such proprietary
rights by implementers or users of this specification can be
obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other
proprietary rights, which may cover technology that may be
required to practice this standard. Please address the
information to the IETF Executive Director.
13. Acknowledgements
The authors would like to thank Pete McCann for suggestions on
security considerations and definition of ALL-ZERO-ONE-ADDR.
Thanks to Kuntal Chowdhury for extensive review and comments on
this draft. Also thanks to Henrik Levkowetz for detailed
reviews and suggestions.
The authors would like to thank Mike Andrews, Madhavi Chandra
and Yoshi Tsuda for their review and suggestions.
14. References
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[1] C. Perkins, "IP Mobility Support for IPv4", RFC 3344, August
2002.
[2] P. Calhoun and C. Perkins, "Mobile IP Network Access Identifier
Extension for IPv4", RFC 2794, March 2000.
[3] D. Senie, "Changing the Default for Directed Broadcasts in
Routers", RFC 2644, August 1999.
[4] S. Alexander and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[5] C. Perkins and P. Calhoun, "Mobile IPv4 Challenge/Response
Extensions", RFC 3012, November 2000.
[6] H. Levkowetz and S. Vaarala, "Mobile IP Traversal of Network
Address Translation (NAT) Devices", RFC 3519, April 2003.
[7] C. Perkins and P. Calhoun, "AAA Registration Keys for Mobile
IP", draft-ietf-mobileip-aaa-key-13.txt, 22 June 2003.
[8] Jari Arkko, et. al., Thoughts on bootstrapping mobility
securely as presented at 57th IETF in Vienna, Austria, 16th
July, 2003
Authors' Addresses
Milind Kulkarni
Cisco Systems Inc.
170 W. Tasman Drive,
San Jose, CA 95134
USA
Email: mkulkarn@cisco.com
Phone:+1 408-527-8382
Alpesh Patel
Cisco Systems Inc.
170 W. Tasman Drive,
San Jose, CA 95134
USA
Email: alpesh@cisco.com
Phone:+1 408-853-9580
Kent Leung
Cisco Systems Inc.
170 W. Tasman Drive,
San Jose, CA 95134
USA
Email: kleung@cisco.com
Phone: +1 408-526-5030
Full Copyright Statement
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Internet Draft Dynamic HA Assignment 28 April 2004
Copyright (C) The Internet Society (2004). This document is
subject to the rights, licenses and restrictions contained in
BCP 78 and except as set forth therein, the authors retain all
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This document and the information contained herein are provided
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MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of
any Intellectual Property Rights or other rights that might be
claimed to pertain to the implementation or use of the
technology described in this document or the extent to which
any license under such rights might or might not be available;
nor does it represent that it has made any independent effort
to identify any such rights. Information on the procedures
with respect to rights in RFC documents can be found in BCP 78
and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of
an attempt made to obtain a general license or permission
for the use of such proprietary rights by implementers or
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The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other
proprietary rights that may cover technology that may be
required to implement this standard. Please address the
information to the IETF at ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by
the Internet Society.
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