Mobile IP Working Group Milind Kulkarni
INTERNET-DRAFT Alpesh Patel
Category: Standards Track Kent Leung
Date : 8 January 2004 Cisco Systems Inc.
Mobile IPv4 Dynamic Home Agent Assignment
draft-ietf-mip4-dynamic-assignment-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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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 Redirected HA address extension..................................5
4. Messaging mechanism for dynamic HA assignment/redirection.........6
4.1 Messaging for dynamic HA assignment..............................6
4.1.1 Example with Message Flow Diagram..............................6
4.2 Messaging for HA redirection.....................................8
4.2.1 Example with Message Flow Diagram..............................9
4.2.2 HA Rejects Registration Request and suggests redirection.......9
5. Mobility Agent Considerations for dynamic HA assignment..........10
5.1 Mobile Node Considerations......................................10
5.1.1 MN using FA CoA...............................................11
5.1.2 MN using Collocated CoA.......................................11
5.1.3 Refreshing Assigned HA Address on Mobile Node.................12
5.2 Foreign Agent Considerations....................................12
5.3 Home Agent Considerations.......................................12
5.3.1 Assigned Home Agent Considerations............................13
6. Requested Home Agent Selection...................................15
7. Error Values.....................................................16
8. IANA Considerations..............................................16
9. Security Considerations..........................................17
9.1 Message Authentication Codes....................................17
9.2 Areas of Security Concern in this Protocol......................17
10. Backward Compatibility Considerations...........................18
11. Change Log......................................................18
12. Intellectual Property Rights....................................18
13. Acknowledgements................................................19
14. References......................................................19
Authors' Addresses..................................................20
Full Copyright Statement............................................20
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.
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
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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-ADDRESS).
Alternately, MN can set the HA field to a unicast address. The
HA receiving the 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 a new extension (REDIRECTED-HA-ADDRESS). The HA
can reject the request if the HA in request does not match any
of its own addresses.
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-ADDRESS).
AAA server: Authentication, Authorization and Accounting
Server.
DNS: Domain Name Service.
DHCP: Dynamic Host Configuration Protocol.
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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 an 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.
Local administrative policies is yet another reason for dynamic
HA assignment/HA redirection during the start of a Mobile IP
session.
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The problem of discovering a Mobile nodeÆs 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 for
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 Redirected HA address extension
The Redirected HA address extension, shown in figure 1,
contains the address of the HA where the MN should attempt the
next registration. It is a skippable extension and MUST be
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included in Registration Reply when the reply code is REDIRECT-
HA-REQ.
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 | Length | Redirected-HA-Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The Redirected HA address Extension
Type REDIRECTED-HA-ADDRESS (skippable) [1]
Length 4
HA-Address The address of redirected HA
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.
2. The MN (if using collocated CoA) or FA (if using FA CoA)
sends the Registration Request to the "Requested HA".
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 |
+-----------------------------------------------------------+
2. The FA sends the Registration Request to the Requested HA.
The Registration Request looks:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| FA |Requested HA| | ALL-ZERO-ONE-ADDR |FA CoA |
+-----------------------------------------------------------+
3. HA processes the Registration Request in accordance with RFC
3344 and the messaging defined in this document and 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).
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+-----------------------------------------------------------+
| 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 or unicast address.
2. The MN (if using collocated CoA) or FA (if using FA CoA)
sends the Registration Request to the "Requested HA".
3. When HA receives the Registration Request, if the unicast
HA address in Request does not match any of its addresses,
HA can reject the request with Reply code REDIRECT-HA-REQ
and suggest an alternate HA.
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-ADDRESS 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.
5. If the error code is set to REDIRECT-HA-REQ, MN obtains
the HA address from REDIRECTED-HA-ADDRESS and sends a
Registration Request to this HA.
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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
4.2.2 HA Rejects Registration Request and suggests redirection
1. MN sets the Home Agent address field in the Registration
Request to ALL-ZERO-ONE-ADDR or unicast HA 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 |
| | | | or unicast addr | |
+-----------------------------------------------------------+
2. The FA sends the Registration Request to the Requested HA.
Note that the Requested HA could be different from the unicast
HA address in the Request. The Registration Request looks:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| FA |Requested HA| | ALL-ZERO-ONE-ADDR |FA CoA |
| | | | or unicast addr | |
+-----------------------------------------------------------+
3. HA processes the Registration Request in accordance with RFC
3344 and the messaging defined in this document. If the
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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-ADDRESS 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-ADDRESS 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-ADDRESS extension |
+-----------------------------------------------------------+
5. If MN can authenticate the Reply, MN extracts the HA address
from REDIRECTED-HA-ADDRESS 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.
A mobile node MUST set the Home Agent field in the Registration
Request to a unicast address or 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
and an individual HA may also be dynamically derived during the
dynamic HA assignment, based on a shared secret between MN and
AAA infrastructure.
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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, it MUST set the
home agent address field in the Registration Request to unicast
address or 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-ADDRESS extension.
5.1.2 MN using Collocated CoA
Mobile Node in collocated CoA mode MUST set the home agent
address field in the Registration Request to unicast address or
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.
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-ADDRESS extension.
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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.
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.
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.
Backward compatibility issues related to the mobility agents
are addressed in section 9.
5.3 Home Agent Considerations
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 own
address in HA field of Reply and sets the Reply code to
REDIRECT-HA-REQ and adds the REDIRECTED-HA-ADDRESS extension.
Home Agent receiving the request with HA field set to a unicast
address not matching any of its addresses MUST reject the
request even if successfully authenticated. This rejected
message has the code 136 as defined in RFC3344 (3.8.3.2). HA
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may reject the message with code REDIRECT-HA-REQ and suggest
an alternate HA to use in the REDIRECTED-HA-ADDRESS extension.
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 Unicast û RFC 3344: Normal HA processing
Same as Dest per RFC 3344.
IP addr
Unicast û RFC 3344: HA denies the
Different registration with error code
than Dest IP 136 and sets HA field to its
Addr own IP address in the reply as
per section 3.8.3.2.
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-
ADDRESS extension.
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2 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
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-
ADDRESS extension
3 Non-unicast Unicast RFC 3344: HA rejects with error
code 136 and sets HA field to
its own IP address in the reply
per section 3.8.2.1.
4 Non-unicast Non-unicast RFC 3344: HA rejects with error
code 136 and sets HA field to
its own IP address in the reply
per section 3.8.2.1.
Table 1: Registration Request handling at Assigned HA
This specification proposes an enhancement to case #1 from RFC
3344. As per this specification, when a HA receives a
Registration Request and the HA address (unicast) does not
match its own address(es), 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
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message and put the address of the redirected HA in the
REDIRECTED-HA-ADDRESS extension.
This specification also proposes a subtle difference in
behavior for case #2 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
redirected HA in the REDIRECTED-HA-ADDRESS 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 first Registration Request in
the Mobile IP session is the Requested HA. This address MUST
be a unicast IP address.
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
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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 û 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.
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 suggested 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
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values conventionally associated with the rejection by the home
agent (i.e. value in the range 128-192).
The extension REDIRECTED-HA-ADDRESS defined in section 3.3
corresponds to a skippable extension.
IANA should record the values as defined in Section 7 and 3.3.
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 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. 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 ôSecurity Considerationsö of RFC-3344.
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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
configured HA. In collocated mode, the endpoint of the MN's
tunnel is the Assigned HA.
11. Change Log
Version 2 is totally revamped from earlier version. The most
notable changes are:
Removed references to directed HA/assigned HA. There is no HA
redirection in the network to incorporate the feedback from
Pete McCann. The single entity is currently called Assigned HA.
Added a new error code for HA rejection when dst IP is unicast
and HA address is unicast and these two addresses are
different. The HA receiving RRQ rejects the RRQ and puts
another HA in RRP and its source address in RRP.
Also, when this new error code is used for HA redirection, a
new HA address is suggested in a new extension
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
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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
[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, July 803.
[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., ôThoughts on bootstrapping mobility
securelyö as presented at 57th IETF in Vienna, Austria, 16th
July, 2003
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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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Reserved.
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notice or references to the Internet Society or other Internet
organizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copyrights
defined in the Internet Standards process must be followed, or
as required to translate it into languages other than English.
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The limited permissions granted above are perpetual and will
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Acknowledgement
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