Mobile IP Working Group Milind Kulkarni
INTERNET-DRAFT Alpesh Patel
Category: Standards Track Kent Leung
Date : 12 December 2005 Cisco Systems Inc.
Mobile IPv4 Dynamic Home Agent Assignment
draft-ietf-mip4-dynamic-assignment-07.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 12, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
Mobile IPv4 [1] 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.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 1]
Internet Draft Dynamic HA Assignment 12 December 2005
Table of Contents
1. Introduction................................................3
2. Requirements Terminology....................................3
3. Problem Statement...........................................4
3.1 Scope.......................................................5
3.2 Dynamic Home Agent Discovery in Mobile IPv4.................5
3.3 NAI usage and dynamic HA assignment.........................6
3.4 Dynamic HA Extension........................................6
3.4.1 Requested HA Extension....................................6
3.4.2 Redirected HA Extension...................................7
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.........................8
4.2 Messaging for HA redirection...............................10
4.2.1 Example with Message Flow Diagram........................11
5. Mobility Agent Considerations..............................12
5.1 Mobile Node Considerations.................................12
5.1.1 MN using FA CoA..........................................13
5.1.2 MN using Co-located CoA..................................14
5.1.3 Refreshing Assigned HA Address on Mobile Node............14
5.2 Foreign Agent Considerations...............................15
5.3 Home Agent Considerations..................................15
5.3.1 Assigned Home Agent Considerations.......................16
6. Requested Home Agent Selection.............................17
7. Error Values...............................................18
8. IANA Considerations........................................18
9. Security Considerations....................................19
10. Backward Compatibility Considerations.....................20
11. Change Log from previous versions.........................21
12. Acknowledgements..........................................22
13. Normative References......................................22
Authors' Addresses.............................................23
Intellectual Property Statement................................23
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 2]
Internet Draft Dynamic HA Assignment 12 December 2005
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 the
Network Access Identifier (NAI) extension [2] when requesting a
dynamically assigned HA.
The MN requests a dynamically assigned HA by setting the HA field in
the initial Registration Request to ALL-ZERO-ONE-ADDR (defined in
section 2). If the request is accepted, the HA sends a successful
Registration Reply containing the HA's own 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).
This document also defines a new Requested HA Extension for use in
Registration Requests when the HA field is set to ALL-ZERO-ONE-
ADDRESS. The Requested HA address is a hint to the network about the
MN's preferred HA.
The messaging mechanism is defined in this document so that the
MN can request and receive a dynamic HA address in Mobile IP
messages. However, the mechanism by which the network selects
an HA for assignment to the MN is outside the scope of this
document. For example, the selection may be made by any
network node that receives the registration request (or
information about the registration request), such as a Foreign
Agent, AAA server, or Home Agent. The node that selects the
HA may select one based on a number of criteria, including but
not limited to HA load-balancing, geographical proximity,
administrative policy etc.
2. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [6].
The Mobile IP related terminology described in RFC 3344 [1] is used
in this document. In addition, the following terms are used:
ALL-ZERO-ONE-ADDR: IP address 0.0.0.0 or 255.255.255.255. An
address of 255.255.255.255 indicates a preference
for an HA in the home domain. An address of
0.0.0.0 indicates no preference for home vs.
visited domain.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 3]
Internet Draft Dynamic HA Assignment 12 December 2005
Requested HA: Destination IP address of Home Agent that the
Registration Request is sent to. Must be a
unicast IP address. This address can be
obtained as described in section 6.
Note that this specification defines a new
"Requested HA Extension" in section 3.4, which
is different from the term "Requested HA".
Assigned HA: The HA that accepts an MN's Registration Request
and returns a 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 System.
DHCP: Dynamic Host Configuration Protocol.
MN: Mobile Node as defined in Mobile IPv4 [1].
HA: Home Agent as defined in Mobile IPv4 [1].
FA: Foreign Agent as defined in Mobile IPv4 [1].
CoA: Care of Address.
CCoA: Co-located 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.
RRQ: Registration Request.
3. Problem Statement
The 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
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 4]
Internet Draft Dynamic HA Assignment 12 December 2005
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 that is
close to the mobile node it can drastically reduce the latency
between the home agent and mobile node.
- 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.
3.1 Scope
This specification does not address the problem of distributing a
security association between the MN and HA, and it can either be
statically preconfigured or dynamically distributed using other
mechanisms [7].
The draft introduces the terms Requested/Assigned/Redirected HA
(section 6). The discovery of candidate HA addresses for insertion
into the Redirected HA Extension can be accomplished through various
means which are network and/or deployment specific and hence are
outside the scope of this specification.
The MN MAY request dynamic HA assignment when it is not aware of any
HA address and even when it is aware of at least one HA address.
3.2 Dynamic Home Agent Discovery in Mobile IPv4
Mobile IPv4 [1] 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. However, 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].
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 5]
Internet Draft Dynamic HA Assignment 12 December 2005
3.3 NAI usage and dynamic HA assignment
The 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 requires that while
using dynamic HA assignment, MN MUST use the NAI and obtain a home
address. MN can still suggest a static home address in the
Registration Request, but must take the address in the Registration
Reply as the home address for the session. This is compatible with
the procedures documented in the NAI specification [2].
3.4 Dynamic HA Extension
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) (to be assigned by
IANA) is the type, which specifies the dynamic HA
address.
Sub-Type Defines the use of this extension as:
sub-type 1 = Requested HA Extension
2 = Redirected HA Extension
Length Indicates the length of the extension not
including the type, sub-type and length fields.
Length is always 4 bytes.
HA-Address Address of the Home Agent.
3.4.1 Requested HA Extension
The Requested HA Extension is a Dynamic HA Extension of subtype 1.
The MN may include the Requested HA Extension in the registration
request as a hint to the network where it wishes to be anchored.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 6]
Internet Draft Dynamic HA Assignment 12 December 2005
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 Registration Request is forwarded to this
HA. In presence of an FA, the FA MUST forward Registration Request
to the HA address in this extension.
3.4.2 Redirected HA Extension
The Redirected HA Extension is a Dynamic HA Extension of subtype 2.
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 sent with a new error code REDIRECT-HA-REQ and
the alternate HA address is specified in this extension.
The Redirected HA Extension MUST be included in Registration Reply
when the reply code is REDIRECT-HA-REQ.
4. Messaging mechanism for dynamic HA assignment/redirection
This specification presents two alternatives for home agent
assignment. The two alternatives are:
(a) Dynamic HA assignment (described in section 4.1) and
(b) HA redirection (described in section 4.2).
4.1 Messaging for dynamic HA assignment
The following sequence of events occurs when the MN requests dynamic
Home Agent assignment:
1. The MN sets the Home Agent address field in the Registration
Request to ALL-ZERO-ONE-ADDR. If the MN is aware of a desired HA
address, it can add that address in the Requested HA Extension in
the Registration Request. If the HA does not support the
Requested HA Extension, see step 2 below.
2. This step is applicable, in lieu of step 1, for a MN that is
aware of the HA address and desires dynamic HA assignment. Also,
the MN follows this (when aware of a HA address) when it
discovers a legacy FA in the path or if the known HA does not
support the Requested HA Extension (see section 10).
The MN sets the Home Agent address field in the Registration
Request to the HA address (instead of setting it to ALL-ZERO-ONE-
ADDR). The MN also adds the same HA address in the Requested HA
Extension in the Registration Request.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 7]
Internet Draft Dynamic HA Assignment 12 December 2005
3. The MN (if using co-located CoA and registering directly with the
HA) or the FA (if the MN is registering via the FA) sends the
Registration Request to the "Requested HA". If the Requested HA
Extension is present, Requested HA is specified in the "HA
Address" of this extension.
Per section 10, in case of a legacy FA, legacy FA forwards the
Registration Request to the address in the HA field of the
Request (thus, MN uses step 2 above in case of legacy FA instead
of step 1).
4. The "Requested HA" is the home agent that processes the
Registration Request in accordance with Mobile IPv4 [1] and as
per the specification in this document. It creates mobility
binding for successful Registration Request. It also sends a
Registration Reply to the MN.
5. 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. (Note that the "Assigned HA" will be same as the
"Requested HA").
6. 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 alternative is best described with the
help of a message flow diagram and description.
Figure 2 shows one specific example of a Mobile Node using an FA-
located Care of Address (FA CoA) and FA understands the Requested HA
Extension per this specification.
Other scenarios such as when the mobile node uses a co-located care
of address and presence of a legacy HA or FA are not described below,
but the behavior is similar.
MN FA Requested/Assigned HA
| 1 | |
|------------>| 2 |
| |--------------->|
| | |
| | |
| | 3 |
| 4 |<---------------|
|<------------| |
| | |
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 8]
Internet Draft Dynamic HA Assignment 12 December 2005
| | 5 |
|----------------------------->|
| | |
Figure 2: Example message flow for dynamic HA assignment
1. The MN sets the Home Agent address field in the Registration
Request to ALL-ZERO-ONE-ADDR. Since the MN is using FA CoA in this
example, it sends the Registration Request to the FA. The
Registration Request is formatted 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 a desired HA address, it can add that address
in the Requested HA Extension in Registration Request as a hint.
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. If the Requested HA Extension is not present, the FA
determines the Requested HA through means outside the scope of this
specification. The Registration Request is formatted as follows:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| FA |Requested HA| | ALL-ZERO-ONE-ADDR |FA CoA |
+-----------------------------------------------------------+
(If MN includes the Requested HA Extension, the FA copies that
extension. The FA then forwards the Registration Request, along with
the Requested HA Extension, to the HA address specified in Requested
HA Extension.)
3. The HA processes the Registration Request in accordance with
Mobile IPv4 [1] and the messaging defined in this document. The HA
creates mobility binding for successful request and becomes the
Assigned HA. The HA then sends Registration Reply to the FA, which
is formatted as follows:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
|Assigned| Src IP of | | Assigned HA |FA CoA/|
| HA | the RRQ | | | |
+-----------------------------------------------------------+
4. The FA relays the Registration Reply to the MN, as follows.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 9]
Internet Draft Dynamic HA Assignment 12 December 2005
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| FA | MN | | Assigned HA |FA CoA/|
+-----------------------------------------------------------+
5. The MN obtains the Assigned HA address from the HA field in the
successful Registration Reply and uses it for the remainder of the
session. The MN sends subsequent Re-Registration or De-Registration
Requests for the remainder session directly to the Assigned HA. The
Home Agent address field in this Registration Request is set to
ALL-ZERO-ONE-ADDR. Note that the Assigned HA is the same as the
Requested HA.
4.2 Messaging for HA redirection
This section describes the events that occur when the Requested HA
does not accept the Registration Request and redirects the mobile
node to another HA (aka Redirected HA) instead. This behavior is not
exhibited by a legacy HA and so is not referred in the description
below. In presence of a legacy FA, please refer to section 4.1 for
the specific field in the Registration Request.
1. The MN sets the Home Agent address field in the Registration
Request to ALL-ZERO-ONE-ADDR.
2. The MN (if using co-located CoA and registering directly with the
HA) or FA (if the MN is registering via the FA) 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 the HA receives the Registration Request, if the HA field is
set to ALL-ZERO-ONE-ADDR, the HA may reject the request with Reply
code REDIRECT-HA-REQ and suggest an alternate HA.
The 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 IP address of the HA that is the target of the redirection 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.
5. If the error code is set to REDIRECT-HA-REQ, MN obtains the HA
address from Redirected HA Extension. The MN then sends a
Registration Request to Redirected HA. The MN may choose to add
Requested HA extension in this new Registration Request. If a
registration loop occurs (the case when the Redirected HA is an HA
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 10]
Internet Draft Dynamic HA Assignment 12 December 2005
that had already directed the MN to register elsewhere) then the
MN stops sending any further Registration Request and provides an
indication that the loop event was detected. The number of
consecutive Redirected HAs remembered by MN for loop detection is
an implementation parameter.
4.2.1 Example with Message Flow Diagram
Figure 3 shows one specific example of a Mobile Node using FA-located
Care of Address, where the FA is not a legacy FA.
MN FA Requested HA Redirected HA
| 1 | | |
|------------>| 2 | |
| |--------------->| |
| | | |
| | | |
| | 3 | |
| 4 |<---------------| |
|<------------| | |
| | | |
| | 5 | |
|--------------------------------------------->|
| | | |
Figure 3: Example message flow for HA redirection
1. The MN sets the Home Agent address field in the Registration
Request to ALL-ZERO-ONE-ADDR. Since the MN is using FA CoA in this
example, it sends the Registration Request to the FA. The
Registration Request is formatted 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 as a hint. 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. If the Requested HA Extension is not present, the FA
determines the Requested HA through means outside the scope of this
specification. The Registration Request is formatted as follows:
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 11]
Internet Draft Dynamic HA Assignment 12 December 2005
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| FA |Requested HA| | ALL-ZERO-ONE-ADDR |FA CoA |
+-----------------------------------------------------------+
3. The HA processes the Registration Request in accordance with
Mobile IPv4 [1] and the messaging defined in this specification. If
the registration is successful, but local configuration/
administrative policy etc. directs HA to refer the MN to another HA,
the HA rejects the Request with error code REDIRECT-HA-REQ. The HA
fills in the address of the Redirected HA in the Redirected HA
Extension. The HA then sends Registration Reply reject to the FA,
which is formatted as follows:
+-----------------------------------------------------------+
| Src IP=| Dest IP = | MN HoA | HA Address = | CoA = |
| | Src IP of | | HA |FA CoA |
| HA | the RRQ | | | |
+-----------------------------------------------------------+
| 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 the MN can authenticate the Reply, the MN extracts the HA
address from the Redirected HA Extension. The MN then sends a
Registration Request to the Redirected HA, unless it has already
received a redirection response from that HA while processing the
Registration Request. The MN may choose to add Requested HA
extension in this new Registration Request.
5. Mobility Agent Considerations
The following sections describe the behavior of each mobility agent
in detail.
5.1 Mobile Node Considerations
The mobile node MUST use the NAI extension for home address
assignment when using the messaging mechanism in this document.
Since MN uses the NAI extension, the Home Address field is set to
0.0.0.0.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 12]
Internet Draft Dynamic HA Assignment 12 December 2005
While dynamic HA assignment is in progress and the MN has not
successfully anchored at a Home Agent, the MN 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 Mobile IPv4 [1] or Mobile IPv4 Challenge/Response
Extensions [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 [7].
The mobile node MUST maintain the remaining Mobile IP session with
the Assigned HA.
As mentioned in the Security Considerations (Section 9), there is a
possibility of more than one HA create a mobility binding entry for a
given MN, if a rogue node in the middle captures the Registration
Request and forwards it to other Home Agents. MN can mitigate such
condition by using a short lifetime (e.g. 5 seconds) in the
Registration Request with Home Agent field set to ALL-ZERO-ONE-ADDR.
The following sections describe MN behavior in FA CoA mode and co-
located CoA mode.
5.1.1 MN using FA CoA
When a mobile node initiates a 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 the 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 a successful Registration Reply is received, the MN obtains the
Assigned HA from the HA field of Reply. The Assigned HA address will
be the same as the Requested HA Extension, if it was included in the
Registration Request by the MN.
If a Registration Reply is received with code REDIRECT-HA-REQ, the 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. The MN MUST put the Redirected HA address
as the Requested HA Extension of the new Registration Request.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 13]
Internet Draft Dynamic HA Assignment 12 December 2005
In some cases, for the first Registration Request the MN may want to
hint to the network to be anchored at a specific HA. The MN SHOULD
put that address in the HA address of the Requested HA Extension.
5.1.2 MN using Co-located CoA
An MN in co-located 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 on how to select a Requested
HA are briefly covered in section 6.
If a successful Reply is received, the MN obtains the Assigned HA
address from the successful Registration Reply. The Assigned HA will
be the same as Requested HA to which the Registration Request was
sent. 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 for the duration of the Mobile IP session, the mobile node will
always be anchored to the assigned home agent with which it was
initially registered.
If a Registration Reply is received with code REDIRECT-HA-REQ, the 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. The MN MUST put the Redirected HA in the
Requested HA Extension of the new Registration Request.
In some cases, for the first Registration Request MN may want to hint
to the network to be anchored at a specific HA and the MN SHOULD put
that address in the HA address of the Requested HA Extension.
While requesting dynamic HA assignment and registering directly with
an HA, the Requested HA Extension MUST be included and MUST contain
the address of the HA to which the Registration Request is sent.
When using co-located CoA but registering via a legacy FA, the HA
field in Reqistration Request may be set to Requested HA.
If the Registration Request contains the Requested HA Extension, the
HA address in that extension MUST match the destination IP of the
Request.
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
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 14]
Internet Draft Dynamic HA Assignment 12 December 2005
mobile node will be always anchored to an optimal home agent from
where it initiated the Mobile IP session.
Alternately, the MN may save the Assigned HA address and use it in
the Requested HA Extension along with ALL-ZERO-ONE-ADDR HA address in
Registration Request for a new Mobile IP session.
5.2 Foreign Agent Considerations
When the mobile node is using a FA CoA it always registers via the
FA. When the MN is using a co-located CoA it may register through a
FA or it may register directly with an HA, unless the R bit is set in
the FA's agent advertisement, in which case it always registers
through the FA.
When the FA receives a Registration Request with HA address field set
to ALL-ZERO-ONE-ADDR that doesn't contain the Requested HA Extension,
the FA obtains the Requested HA address to forward the Registration
Request using means outside the scope of this specification. Some
ideas on how to select a Requested HA are briefly covered in section
6.
If the FA cannot obtain the Requested HA to which 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, the FA MUST
forward Registration Request to the address in this extension. If
the HA address in this extension is not a routable unicast address,
the FA MUST reject request with error code NONZERO-HA-REQD.
If the Registration Request contains the Requested HA Extension, the
FA uses that address as the destination for the relayed Registration
Request.
Backward compatibility issues related to the mobility agents are
addressed in section 10.
5.3 Home Agent Considerations
A Home Agent can process an incoming Registration Request in one of
the following two ways:
1. The MN or FA sends the Registration Request to the Requested HA.
The term Requested HA has meaning in the context of a Registration
Request message. When the Requested HA successfully processes the
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 the context of a Registration Reply message.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 15]
Internet Draft Dynamic HA Assignment 12 December 2005
2. A Home Agent receiving a Registration Request with HA field set
to ALL-ZERO-ONE-ADDR MAY reject the request even if successfully
authenticated 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. If it does not match, the Requested HA MUST reject the
Registration Request with error code 136.
5.3.1 Assigned Home Agent Considerations
The HA that processes the incoming Registration Request fully in
accordance with Mobile IPv4 [1] and this specification becomes the
Assigned HA. The Registration Request terminates at the Assigned HA.
The Assigned HA creates one mobility binding per MN 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.
The following table summarizes the behavior of the Assigned HA, based
on the value of the destination IP address and Home Agent field of
the Registration Request.
Dest IP Addr HA field Processing at Assigned HA
------------ ------------ ----------------------------------
Unicast non-unicast Mobile IPv4 [1]: There is no change
in handling for this case from
(Must be Mobile IPv4. It is mentioned here
equal to the for reference only.
HA receiving HA denies the registration with
the RRQ) error code 136 and sets HA field to
its own IP address in the reply as
per section 3.8.3.2 in [1].
ALL-ZERO- New Behavior: Accept the RRQ as per
ONE-ADDR 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: If authentication is
successful, reject RRQ with a new
error code REDIRECT-HA-REQ. HA
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 16]
Internet Draft Dynamic HA Assignment 12 December 2005
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
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. Therefore, this document does not
specify any new behavior for the case where the HA receives a subnet
directed broadcast Registration Request as specified in section
3.8.2.1 of the Mobile IPv4 specification [1]. 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 Mobile IPv4 [1] section
3.8.3.2.
When the destination IP address is a unicast address and the Home
Agent field is ALL-ZERO-ONE-ADDR, the HA accepts/denies registration
and sets the HA field to its own IP address in the reply (i.e. the
registration is not rejected with error code 136).
The 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 other
reasons. The HA puts its own address in HA field of the Registration
Reply message and puts the address of the redirected HA in the
Redirected HA Extension. If the HA accepts the Request, it sets the
HA field in the Registration Reply to its own address.
The Requested HA always performs standard validity checks on the
Registration Request. If there is any error, the Registration
Request is rejected with error codes specified in Mobile IPv4 [1].
6. Requested Home Agent Selection
When dynamic HA assignment is requested, the MN (or FA in the case of
registration via FA) sends the Registration Request to 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 example methods by which the MN or the FA may select the
Requested HA are briefly described below:
DHCP:
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 17]
Internet Draft Dynamic HA Assignment 12 December 2005
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 a 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 the hostname of the HA is configured on the 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 a resource record with information to
identify the optimal HA to the MN. The MN sends a Registration
Request directly to the HA and receives the Assigned HA to be used
for remainder of the Mobile IP session.
Static configuration:
The HA address is statically configured on the MN. The MN sends the
Registration Request to the configured address. The Requested HA may
then redirect the MN to a Redirected HA.
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 Reregister with redirected HA.
8. IANA Considerations
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 18]
Internet Draft Dynamic HA Assignment 12 December 2005
The code value NONZERO-HA-REQD is a Mobile IP response code [1] taken
from the range of values associated with rejection by the foreign
agent (i.e. value in the range 64-127).
The code value REDIRECT-HA-REQ is a Mobile IP response code [1] taken
from the range of values associated with rejection by the home agent
(i.e. value in the range 128-192).
The Dynamic HA Extension is assigned from the range of values
associated with skippable extensions at the home agent (i.e. value in
the range 128-255).
IANA should record the values as defined in Section 7 and 3.4.
9. Security Considerations
This specification assumes that a security configuration has been
preconfigured between the MN and the HA or is configured along with
the initial Registration Request/Registration Reply as per [7].
There is a possibility of more than one HA create a mobility binding
entry for a given MN, if a man in the middle captures the
Registration Request with HA field set to ALL-ZERO-ONE-ADDR and
forwards it to other HAs. This scenario assumes that the rogue node
can find out the addresses of the HAs which are able to authenticate
the Registration Request. It also assumes that the rogue node has
the capability to store, duplicate, and send packets to the other HAs
within the limited time of the replay window. Otherwise these HAs
will reject the Registration Requests anyway. In addition, this type
of attack is only possible when the Requested HA Extension is not
included in the registration message. The Mobile Node can minimize
the duration of this condition by using a short lifetime (e.g. 5
seconds) in the Registration Request.
This specification does not change the security model established in
Mobile IPv4 [1]. Mobile Nodes are often connected to the network via
wireless links, which may be more prone to passive eavesdropping or
replay attacks. Such an attack might lead to bogus registrations or
redirection of traffic or denial of service.
As per the messaging in this draft, the Assigned Home Agent will
process the incoming Registration Request as per Mobile IPv4 [1].
Hence the Assigned Home Agent will have same security concerns as
that of the Home Agent in Mobile IPv4 [1]. They are addressed in
Section 5 "Security Considerations" of Mobile IPv4 [1].
The Registration Request and Registration Reply messages are
protected by a valid authenticator as specified in Mobile IPv4 [1].
Configuring security associations is a deployment specific issue and
is covered by other Mobile IP specifications. There can be many ways
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 19]
Internet Draft Dynamic HA Assignment 12 December 2005
of configuring security associations, but this specification does not
require any specific way.
An example is where the security association between an MN and an
individual HA (Requested or Assigned) is dynamically derived during
the registration process 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 MN-HA Authentication Extension. Because 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 each Registration Request from
the mobile node as specified in Mobile IPv4 [1] and/or RFC-3012. The
MN also authenticates the Registration Reply from the Assigned HA,
thus the existing trust model in Mobile IPv4 [1] is maintained.
10. Backward Compatibility Considerations
In this section, we examine concerns that may arise when using this
specification in a mixed environment where some nodes implement the
specification and others do not. In each of the examples below, we
consider the case where one node is a "Legacy" node which does not
implement the specification in the context of other nodes which do.
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 Registration Request is set to ALL-ZERO-ONE-ADDR.
Legacy Foreign Agent:
Legacy foreign agents may forward a 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. The MN
may not be aware of the dropped Registration Request and may probably
retry registration, thereby increasing the delay in registration.
To reduce the delay in registration, the MN should take following
steps:
1. The MN should send the Registration Request as specified in this
specification. In other words, the MN should set the home agent
field in the Registration Request to ALL-ZERO-ONE-ADDR and also add
the Requested HA Extension.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 20]
Internet Draft Dynamic HA Assignment 12 December 2005
2. If the MN does not receive a Registration Reply within some time
and/or after sending a few Registration Requests, it can assume
that the Registration Request(s) has been dropped, either by a
legacy FA or an incorrect HA. In addition, if the registration is
denied with error code 70 (poorly formed Request), the MN can
assume that the legacy FA cannot process this message. In either
case, the MN should fall back to a recovery mechanism. The MN
should quickly send a new Registration Request as mentioned in
section 4.1 step 2. This step will ensure that a legacy FA will
forward the Registration Request to the Home Agent thereby making
dynamic HA assignment possible.
Legacy Mobile Node:
A MN that sends a registration request to an FA which can do dynamic
HA assignment, but does not set the HA field to ALL-ZERO-ONE-ADDR
will continue to be registered with its statically configured HA,
exactly according to RFC 3344.
11. Change Log from previous versions
Note: This section should be removed before publication.
Changes from revision 6 to 7:
1. Updated section 4.2 bullet 5.
Changes from revision 5 to 6:
2. Updated section 4.2.1 bullet 5.
3. Fixed nits found by idnit tool.
4. Added text in section 5.1 outlining how to avoid the
possibility of multiple bindings on HAs by requiring short
lifetime for first registration request.
5. Added text in section 9 outlining possibility of multiple
bindings on HAs.
6. Added text in section 12 Acknowledgements.
Changes from revision 4 to 5:
1. Legacy FA Considerations text was updated based on the WG
discussions which addressed IESG review feedback.
Changes from revision 3 to 4:
1. Text added to clarify the cases when MN is configured with HA
address and not configured with HA address and requests
dynamic HA assignment.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 21]
Internet Draft Dynamic HA Assignment 12 December 2005
2. Clarification on legacy FA section as suggested by Thomas
Narten.
3. More editorial changes suggested by the chairs.
Changes from revision 2 to 3:
1. More editorial changes suggested by the chairs.
Changes from revision 1 to 2:
1. Editorial changes suggested by the WG, the chair's reviews and
idnits.
Changes from revision 0 to 1:
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. Acknowledgements
The authors would like to thank Pete McCann for thorough review,
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. Thomas Narten highlighted issues for legacy
FA considerations. Thanks to Ahmad Muhanna for pointing out scenario
of multiple bindings on HAs, documented in the Security
Considerations section.
The authors would like to thank Mike Andrews, Madhavi Chandra and
Yoshi Tsuda for their review and suggestions.
13. Normative 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] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 22]
Internet Draft Dynamic HA Assignment 12 December 2005
[7] C. Perkins and P. Calhoun, "AAA Registration Keys for Mobile
IP", draft-ietf-mip4-aaa-key-06.txt, June 2004.
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
Intellectual Property Statement
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 users of this
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 23]
Internet Draft Dynamic HA Assignment 12 December 2005
specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr.
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.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Kulkarni, Patel, Leung Expires June 12, 2006 [Page 24]
