Abstract:
Methods and apparatus for enhancing Mobile IP signaling and to support use of disparate addressing plans and dynamic Home Agent allocation in Mobile IP Regional Tunneling are described. The enhanced methods of signaling use an intermediate node, e.g., a Gateway Foreign Agent, straddling different addressing domains, when the signaling controls a process between the intermediate node and an upstream node. The specific intermediate node, its interfaces and upstream addresses can be dynamically selected. The Enhanced MIP signaling includes dynamic allocation of: a regional node at a Foreign Agent, the upstream address of a regional node by the regional node, a Home Agent for a regional node prior to dynamic allocation of the regional node. A method is supported to indicate to a Mobile Node that a dynamically allocated regional node has become invalid triggering enhanced MIP signaling dynamically allocating a new regional node and upstream interface address.

Description:
RELATED APPLICATIONS 
     The present application is a continuation of pending U.S. patent application Ser. No. 12/099,026, now U.S. Pat. No. 8,559,411, filed on Apr. 7, 2008, titled SUPPORT OF DISPARATE ADDRESSING PLANS AND DYNAMIC HA ADDRESS ALLOCATION IN MOBILE IP, and which claims the benefit of the filing date of U.S. patent application Ser. No. 10/408,726, now U.S. Pat. No. 7,356,020, filed on Apr. 7, 2003, titled SUPPORT OF DISPARATE ADDRESSING PLANS AND DYNAMIC HA ADDRESS ALLOCATION IN MOBILE IP, and which claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/370,836 filed Apr. 8, 2002, titled “METHODS AND APPARATUS FOR THE SUPPORT OF DISPARATE ADDRESSING PLANS AND DYNAMIC HA ADDRESS ALLOCATION IN MOBILE IP REGIONAL TUNNELING.” Each of the preceding identified US patent applications are hereby expressly incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     For the purpose of understanding the invention it is useful to have a basic understanding of Mobile IP. Mobile IP (v4/v6), also indicated as MIPv4 [MIPv4] and MIPv6 [MIPv6], enables a mobile node (MN) to register its temporary location indicated by a care-of-address (CoA) to its Home Agent (HA). The HA then keeps a mapping (also called a binding) between the MN&#39;s permanent address, otherwise called Home Address (HoA), and the registered CoA so that packets for that MN can be redirected to its current location using IP encapsulation techniques (tunneling). 
     The CoA used by a MN can be an address that belongs to a Foreign Agent (FA) when MIPv4 is used or, in MIPv4 and MIPv6, it can be a temporarily allocated address to the MN itself in which case is called a collocated care-of-address (CCoA). 
     The concepts and solutions described here are applicable to both MIPv4 and MIP unless otherwise mentioned. 
     Regional tunneling (REGTUN) is one technique sometimes used in conjunction with Mobile IP. This approach uses a Gateway Foreign Agent (GFA) between the FA and the HA to improve MIP signaling. Specifically, the MN can register the local GFA CoA into the HA using an MIP registration with the HA that is routed via the GFA. Then each binding update under the same GFA goes just to the GFA instead of the HA, and changes the FA CoA for the GFA. The GFA switches the GFA CoA traffic for the specific HoA into the FA CoA matching that HoA and GFA CoA. The GFA update is a regional registration and it avoids having to refresh the HA on each hand-off which is a bandwidth and latency gain because the HA could be a very distant node from the FA/GFA. 
     The problem with this draft (http://www.ietf.org/proceedings/01dec/I-D/draft-ietf-mobileip-reg-tunnel-05.txt) is that the signaling scheme assumes that the two addressing schemes are the same either side of the GFA, and no support is enabled for dynamic HA allocation, both of which are common requirements in MIP. Therefore, a need exists for apparatus and methods that will support disparate addressing plans and dynamic HA address allocation in MIP signaling. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to methods and apparatus establishing communications sessions and, more particularly, to enhanced methods of performing signaling through an intermediate node that straddles different addressing domains, when that signaling is trying to control a process undertaken between the intermediate node and an upstream node. Various methods for enhancing Mobile IP discovery of the IP addresses of Mobile IP nodes, and the subsequent configuration of Mobile IP forwarding tunnels is then described. 
     In accordance with one feature of the present invention, rather than allow a downstream node to use the address of the downstream interface on an intermediate node, that is in the same addressing domain as the downstream node, for undertaking a process with the upstream node, in accordance with the present invention, the address of the upstream interface of the intermediate node, that is in the same addressing domain as the upstream node, is instead selected to be the address on the intermediate node for the communications process with the upstream node. This ensures that the upstream node can communicate with the intermediate node for the identified process, even when the two addressing domains are different and the downstream interface of the intermediate node is not reachable from the upstream node. In the case of Mobile IP, the communications process is the MIP tunneling between, for example, an upstream Home Agent and an intermediate regional node such as a Gateway Foreign Agent, which is configured using a MIP Registration Request message from the downstream foreign agent. This then ensures that the tunnel be correctly set-up even when private addresses are used between the foreign agent and the regional node whilst public addresses are used between the regional node and the home agent. Existing Mobile IP signaling instead uses a single piece of information to identify the address of the regional node and the process address for the upstream node with the regional node, which fails in the case of distinct addressing domains on either side of the regional node. 
     Further, in accordance with this invention, the specific intermediate node, as well as the upstream interface and therefore the upstream address at that intermediate node, can all be dynamically selected during the signaling phase, based on information about the type of communications process being set-up, the entity and its location that is requesting that it be set-up, and the type and location of the upstream node. This novel feature of the invention is particularly useful for supporting multiple intermediate nodes in a domain, each of which serves a subset of all the downstream nodes in a domain, and for ensuring that the selected upstream interface of the selected intermediate node is in the same addressing domain as the upstream node. In the specific case of Mobile IP, the present invention enables the regional node to be dynamically allocated at the foreign agent, optionally with the assistance of the Authentication, Authorization and Accounting (AAA) system, and the upstream address of the regional node to be dynamically allocated by the regional node itself, optionally again with assistance from the AAA system. This then avoids all Mobile Nodes having to be configured with, or discover, a table that lists all possible HAs and the associated regional node and upstream interface at that regional node that matches that particular Home Agent. Existing MIP signaling relies on the address of the regional node being known at the foreign agent, and optionally communicated to the Mobile Node in advance of the Registration signal being sent from the Mobile Node, that will traverse the regional node towards the Home Agent. This clearly does not facilitate dynamic allocation of the regional node, nor the dynamic allocation of the associated upstream interface address. 
     Inventive methods, in accordance with the present invention, are also described for dynamically allocating the Home Agent in advance of dynamically allocating the associated regional node, and for communicating the addresses of these dynamically allocated nodes to the other Mobile IP nodes that need that address information for subsequent Mobile IP signaling. The address of the HA should be communicated to the regional node so that the regional node can forward the Registration message to that HA and invoke the tunnel building process between the HA and the regional node. Existing MIP signaling for the regional node does not support dynamic allocation of a HA. 
     Another novel method, in accordance with the present invention, is described for indicating to a Mobile Node when the allocated regional node, that was dynamically allocated to the Mobile Node, becomes invalid, triggering another MIP signaling phase from the Mobile Node to dynamically allocate a new regional node and associated upstream interface address. This method is in contrast to existing MIP signaling which cannot accommodate a dynamically allocated regional node. 
     Numerous additional features and benefits of the present invention will be apparent in view of the Figures and detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates two addressing domains; the generic downstream, intermediate and upstream nodes; and the signals employed to invoke the process between the upstream node and the upstream interface of the (intermediate) node. 
         FIG. 2  illustrates a diagram of an exemplary network supporting a Mobile IP Regional node and the Mobile IP signals used to invoke and manage the tunnel between the Home Agent and the regional node, as well as the tunnel between the regional node and the foreign agent. 
         FIG. 3  illustrates the MIP signaling flow for the dynamic allocation of the regional node, and the interface on that regional node, in the case of a Gateway Foreign Agent, as well as the discovery of a change of regional node. 
         FIG. 4  illustrates the MIP extensions used to carry the dynamically allocated GFA and GFA CoA to the necessary MIP nodes. 
         FIG. 5  illustrates the dynamic allocation of a Home Agent in the presence of a regional node, as well as the MIP signaling changes when the generic intermediate node is additionally a foreign agent that straddles two addressing domains. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The methods and apparatus of the present invention are directed to a number of procedures to enable the IP signaling layer (MIP or similar mechanisms) to better support the existence of a regional node. 
       FIG. 1  shows an overall communication domain  100  including an exemplary addressing domain 1  101  and an exemplary addressing domain 2  103 . Addressing domain 1  101  includes a downstream node  102 ; addressing domain 2  103  includes an upstream node  106 . An intermediate node  104  is located on a boundary  105  separating addressing domain 1  101  from addressing domain 2  103 . Intermediate node  104  includes two addressing interfaces: addressing domain 1 interface  104   a  and addressing domain 2 interface  104   b . Intermediate node  104  also includes address information  104   a ′ associated with interface  104   a  and address information b  104   b ′ associated with interface  104   b . Downstream node  102  may be, for example, a visited access node; intermediate node  104  may be, for example, a MIP Gateway Foreign Node; upstream node  106  may be, for example, a Mobile IP Home Agent. 
     The downstream node  102  and the intermediate node  104  have interfaces with addresses,  102 ′ and  104   a ′, respectively, from the addressing domain 1  101 , such that messages can flow from the downstream node  102  to the downstream interface of the upstream node  104   a . The upstream node  106  and the intermediate node  104  have interfaces with addresses,  106 ′ and  104   b ′, respectively, from the addressing domain 2  103 , such that messages can flow from the upstream interface of the intermediate node  104   b  to the upstream node  106 . 
       FIG. 1  further shows instructed processes  130 , as illustrated by the dashed bi-directional arrows between the upstream node  106  and the intermediate node  104 . The process  130  may be, for example, the invocation and management of a tunnel. 
     When the addressing domain 1  101  and addressing domain 2  103  are independent addressing domains, such that reachability is not supported between those addressing domains, then messages are not generally able to flow between the upstream node  106  and the downstream interface of the intermediate node  104   a , such that any process  130  undertaken between the upstream node  106  and the intermediate node  104 , needs to be undertaken using the interface address  104   b′.    
     To invoke such a process  130  from the downstream node  102 , or any node further downstream of the downstream node  102 , a message 1,  110 , is first sent from the downstream node  102  to the intermediate node  104  using interface  104   a , possibly as a result of an incoming message from a node further downstream of the downstream node  102 . Message 1,  110 , includes a message header  112  which includes source and destination addresses,  111 ,  113 , respectively, equal to the addresses of the downstream node  102 ′ and the downstream interface of the intermediate node  104   a ′, respectively. Message 1,  110 , also includes a message body  114  that includes an instruction  115  to invoke the process  130  between the upstream node  106  and the intermediate node  104 . The Message body 1,  114 , also includes an information element indicating the intermediate node downstream address  104   a ′ that has been dynamically allocated at the downstream node  102 . The message body 1  114  may additionally contain the intermediate node upstream address  104   b ′, which without loss of generality may be empty. The information in the message body 1  114  is typically signed by the downstream node  102  as represented by security information  116  to prevent its contents being manipulated by an attacker situated between the downstream node  102  and the intermediate node  104 . 
     To further invoke such a process  130  from the intermediate node  104 , a message 2,  120 , is first sent from the upstream interface of the intermediate node  104   b  to the upstream node  106 . Message 2,  120 , includes a message 2 header  122  which includes source and destination addresses,  121 ,  123 , respectively, equal to the addresses of the intermediate node upstream interface  104   b ′ and the upstream node  106 ′, respectively. Message 2,  120 , also includes a message 2 body  124  that includes an instruction  125  to invoke the process  130  between the upstream node  106  and the intermediate node  104  that was obtained from message 1,  110 . The Message body  2 ,  124 , also includes an information element indicating the intermediate node downstream address  104   a ′ that has been dynamically allocated at the downstream node  102 . The message body 2  124  also includes the intermediate node upstream address  104   b ′, which was generated at the intermediate node  104 . The information in the message body 2  124  is typically signed, as indicated by security information  126 , by the intermediate node  104  to prevent its contents being manipulated by an attacker situated between the intermediate node  104  and the upstream node  106 . Without loss of generality, the generation of the upstream address  104   b ′ at the intermediate node  104  can be undertaken in a number of ways. Firstly, it can be obtained from message body 1,  114 , if the intermediate node upstream address  104   b ′ was dynamically allocated at the downstream node  102  along with the downstream address  104   a ′. Secondly, the intermediate node upstream address  104   b ′can be dynamically allocated at the intermediate node  104  itself and inserted into message body 2  124  instead of any empty or default value passed in message body 1,  114 . Thirdly, the upstream address on the intermediate node  104   b ′ can be requested and obtained by either the downstream and/or intermediate nodes  102 , 104  from an external policy server such as an Authentication, Authorization and Accounting Server. 
     The upstream node  106  can then invoke the process  130  with the upstream address  104   b ′ of the intermediate node  104 . In addition, messages  140  and  150  are then used to carry the dynamically allocated addresses  104   a ′ and  104   b ′ back to the downstream node  102  and to any nodes further downstream from the downstream node  102  that needs those addresses  104   a ′,  104   b ′ to repeatedly invoke the process  130  via that intermediate node  104 . 
     This sequence ensures that the process  130  from the upstream node  106  does not use the downstream address  104   a ′ of the intermediate node  104  which in the case of separate addressing domains may not be reachable. 
     The application of the above sequence will now be explained, without loss of generality, for the specific case of the downstream node  102  being a MIP foreign agent, the upstream node  106  being a MIP home agent, the intermediate node  104  being a MIP regional node such as Gateway Foreign Agent, and the process  130  being the construction of a MIP tunnel between the MIP Home Agent and the Gateway Foreign Agent on request from a Mobile Node. 
       FIG. 2  shows an exemplary communications network  200  including 3 addressing domains: addressing domain 1  201 , addressing domain 2  203 , and addressing domain 3  207 . Boundary line  205  separates addressing domain 1  201  from addressing domains  203  and  207 . Boundary line  209  separates addressing domain 2  203  from addressing domain 3  207 . 
     The exemplary communications network  200  comprises a visited access node  214 , e.g. a visited access router, including a Mobile IP foreign agent (FA)  216 , a Mobile IP Gateway foreign agent (GFA)  230 , and a Mobile IP Home agent (HA)  240 . The GFA  230  is located on the boundary  205  between addressing domain 1  201  and addressing domain 2  203 . Within addressing domain 1  201 , the GFA  230  is connected to the FA  216  via a node  208  and links  204  and  202 . Within addressing domain 2  203 , the GFA  230  is connected to the HA  240  through nodes  238  and  248  via links  234 ,  206  and  244 . Link  234  couples GFA  230  to node  238 ; link  206  couples node  238  to node  248 ; link  244  couples node  244  to HA  240 . The GFA  230  therefore has two different interfaces, such that a GFA interface  230   a  on link  204  has an address from the same addressing domain 1  201  as that of the FA  216  interface connected to link  202 . In contrast, a GFA  230  interface  230   b  attached to link  234  has an address allocated from the same addressing domain 2  203  as the address allocated to the interface on the HA  240  connected to link  244 . In the communications network  200  it can be seen that no path exists between the HA  240  and the FA  216  that does not traverse the GFA  230 . In addition, the addresses from the addressing domain 1  201  shared by the FA  216  and the GFA  230  are not routable from the addresses from the addressing domain 2  203  shared by the HA  240  and the GFA  230 . 
     Exemplary end node 1  260  and exemplary end node N (X)  262  are coupled to the communications network  200  through the visited access node  214 . Specifically, links  218 ,  220  couple end nodes  260 ,  262 , respectively, to visited access node  214  with its FA  216 . The end nodes  260 ,  262  may be, for example, mobile nodes or mobile terminals. Many such end nodes  260 ,  262  and visited access nodes  214  will typically exist in communications network  200 , along with a smaller number of GFAs  230 . Each such GFA  230  will be assigned to a subset of the visited access nodes  214 , and advertised to the end nodes  260 ,  262  which contain MIP Mobile Node software. The movement of the end nodes  260 ,  262  between visited access nodes  214  can eventually result in the end node receiving a newly advertised GFA  230  address, this address being that of the interface  230   a  connected to link  204  which can be known to the FA  216 . Whilst the exemplary Mobile Node (MN) N (X)  262  receives the same GFA  230  address from any FA  216 , the MN  262  can issue MIP Regional Registration messages  272  towards the GFA  230 , potentially via the FA  214 . This message  272  updates the Care of Address in the GFA  230  for the home address of the MN  262 , this care of address being either the FA  216  address or the address of the MN  262 , such that a tunnel can be constructed between the GFA  230  and the Care of address. The Registration Reply message  273  is then returned to the MN  262  visiting the same MIP nodes as that visited by the Registration message. 
     In order to further explain variations of the present invention, the connectivity between addressing domain 3  207  and addressing domain 2  203  is described below. Dotted arrow line  290  represents the transition of exemplary end node N (X)  262  from addressing domain 1  201  to addressing domain 3  207 . Addressing domain 3  207  includes a visited access node  214 ′, with a mobile IP Foreign agent module  216 ′, and node  208 ′. Link  202 ′ couples FA  216 ′ to node  208 ′. Node  208 ′ is coupled to a MIP Gateway Foreign Agent Node  230 ′ via link  204 ′. Addressing domain 2  203  further comprises node  238 ′ which is coupled to node  248  via link  206 ′. Node  238 ′ is also coupled to GFA  230 ′ via link  234 ′. 
     MIP Gateway Foreign Agent Node  230 ′ is located on the boundary, indicated by dashed line  209 , between addressing domain 2  203  and addressing domain 3  207 . GFA  230 ′ includes interfaces  230 ′ a  and  230 ′ b . The GFA  230 ′ therefore has two different interfaces, such that the GFA interface  230 ′ a  on link  204 ′ has an address from the same addressing domain 3  207  as that of the FA  216 ′ interface connected to link  202 ′. In contrast, the GFA  230 ′ interface  230 ′ b  attached to link  234 ′ has an address allocated from the same addressing domain 2  203  as the address allocated to the interface on the HA  240  connected to link  244 . 
     When however, the MN  262  receives a new GFA  230 ′ address from the FA  216 ′, then the MN  262  knows that no MIP tunnel exists between the Home Agent  240  of the MN  262  and the GFA  230 ′ and, in accordance with the invention, therefore issues a MIP Registration message  270  towards the HA  240 , that is forwarded via the FA  216 ′ and the GFA  230 ′. This message is followed by a Registration Reply message  271  back to the MN  262  via the same set of MIP nodes. The message  270  includes a Care of address field, which is typically populated by the MN  262 , using the GFA  230 ′ address advertised by the FA  216 ′, this typically being the address of interface  230   a ′ at the GFA  230 ′. The message  270  installs the Care of address of the GFA  230 ′ into the HA  240  so that a MIP tunnel can be built for the MN  262  home address between the HA  240  and the GFA  230 ′. Packets will then be delivered to the new GFA  230 ′ and messages  272  and  273  can then update the GFA  230 ′ with each new MN CoA as the MN changes FA  216 ′ under the same GFA  230 ′. This procedure however fails if the address of the GFA  230 ′ on link  204 ′ is not reachable from the HA  240 . Alternative signaling as shown in  FIGS. 3 to 5  and described next may instead be used, in accordance with the present invention. 
       FIG. 3  shows the dynamic allocation of the GFA  230  at the FA  216 , and the dynamic allocation of the GFA CoA at the GFA  230 . The FA  216  of  FIG. 3  equates to the downstream node  102  of  FIG. 1 , the GFA  230  of  FIG. 3  equates to the intermediate node  104  of  FIG. 1  and the HA  240  equates to the upstream node  106  of  FIG. 1 .  FIG. 3  is separated into an addressing domain 1  201  including MN  262  and FA  216  and an addressing domain 2  203  including HA  240 . GFA  230  is situated on a boundary  205  separating domains  201  and  203 . The process  130  of  FIG. 1  equates to the MIP tunnel management between the HA  240  and the GFA  230  of  FIG. 2 . Message  270  of  FIG. 2  is broken up into hop by hop messages  270   a ,  270   b  and  270   c . Message  110  of  FIG. 1  equates to message  270   b  of  FIG. 3  and message  120  of  FIG. 1  equates to message  270   c  in  FIG. 3 . The downstream interface address  104   a ′ on the intermediate node equates to the GFA address in  FIG. 3  whilst the upstream interface address  104   b ′ of the intermediate node equates to the GFA CoA in  FIG. 3 . 
     In step  301 , the FA  216  constructs a message  310  with the FA CoA address from domain 1  201  and GFA address from domain 1  201  advertised to MN  262  for movement detection purposes, and sends the message  310  to the MN  262 . The subsequent messaging of  FIG. 3  is triggered when the MN  262  receives message  310  from FA  216 , which includes a new default GFA address, and which acts as a common identifier for any dynamically allocated GFA at that FA  216 . This means that if the MN  262  sees a new default GFA address then it must also acquire a new dynamically allocated GFA. Message  310  also includes the FA CoA of the FA  216  as is usual in MIP signaling. 
     Next, in step  303 , the MN  262  then sends Registration message  270   a  to the FA  216  including the Home address and HA  240  address of the MN  262 , with the intention of updating the GFA CoA for that home address at the HA  240 . The Registration message  270   a  includes a CoA field that can either be left blank by the MN  262  or can contain the default GFA address. In step  305 , FA  216  then dynamically allocates a GFA to the MN  262 , potentially with help from a policy server, e.g. a AAA server, that has an upstream interface that is reachable from the HA  240  included in the message  270   a . Note that the HA is globally unique through the combination of the HA address and the realm part of the Network Address Identifier of the MN  262  that are included in message  270   a . The GFA address and the FA CoA are then securely passed to the assigned GFA in message  270   b . The FA CoA enables the GFA to build a tunnel to the present FA  216  of the MN  262  whilst the GFA address is included so it can be passed to the HA  240 . In step  307 , the GFA  230  then dynamically assigns a GFA CoA from an interface that is reachable from the HA  240  and then securely passes this address, along with the GFA address to the HA in message  270   c . It does this by adding an extension to the MIP Registration message containing the GFA CoA, that is used instead of the CoA field which is either blank or includes the default GFA address, for construction of the MIP tunnel. The HA  240  can then build that tunnel towards the GFA CoA rather than towards the GFA address, because the GFA address is not itself reachable from the HA  240 . Next, in step  309 , the HA  240  includes the GFA and GFA CoA into the MIP Registration Reply message  271   a , signs this message with the secret it shares with the MN  262 , and sends message  271   a  to the GFA  230 . In step  311 , the GFA  230  forwards the GFA and GFA CoA to the FA  216  in MIP Registration Reply Message  271   b . Subsequently, in step  313 , FA  216  forwards the GFA and GFA CoA to MN  262  in MIP Registration Reply Message  271   c . Finally, in step  315 , MN  262  can then securely receive the GFA and GFA CoA which it can then include in subsequent MIP Registration messages  270  and  272  to refresh the installed MIP bindings in the HA and the GFA. 
     Note that, in other variations of the present invention, the GFA and GFA CoA can be passed back to the MN  262  in many other ways than via the HA, that make use of a different set of MIP security associations to sign the extension carrying those addresses. Note also that in another variation of the present invention, the GFA CoA can instead be dynamically assigned at the same time as the GFA is assigned at the FA, and the GFA CoA then passed in message  270   b  to the allocated GFA. 
       FIG. 4  repeats the elements ( 262 ,  216 ,  230 ,  240 ), domains ( 201 ,  203 ) and boundary  205  of  FIG. 3 . Steps ( 301 ′,  303 ′,  305 ′,  307 ′,  309 ′,  311 ′,  313 ′,  315 ′) of  FIG. 4  equate to the steps ( 301 ,  303 ,  305 ,  307 ,  309 ,  311 ,  313 ,  315 ) of  FIG. 3 , respectively. Similarly, messages ( 310 ′,  270   a ′,  270   b ′,  270   c ′,  271   a ′,  271   b ′,  271   c ′) of  FIG. 4  equate to messages ( 310 ,  270   a ,  270   b ,  270   c ,  271   a ,  271   b ,  271   c ) of  FIG. 3 , respectively. 
     In addition,  FIG. 4  shows the extensions used to carry the FA CoA, GFA CoA and the GFA address in messages  270 ′ and  271 ′. The Hierarchical Foreign Agent Extension (HFAext) carries the FA CoA in message  270   b ′ and carries the GFA CoA in message  270   c ′ and messages  271 ′. Note that if the GFA CoA is also assigned at the FA  216  then two HFAext are included in message  270   b ′, which means that either a flag bit is required in the HFAext to distinguish between the two addresses, or the FA CoA is signed with the secret shared between the FA  216  and the GFA  230  whilst the GFA CoA is signed with the secret shared between the FA  216  and the HA  240 , the type of signature therefore uniquely identifying the contents of each HFAext. The GFA address is carried in the Hierarchical Foreign Agent IP address extension (HFAIPext) in messages  270   b ′,  270   c ′ to the HA  240 , and messages  271 ′ back to the MN  262 . 
     The steps and signaling of  FIG. 4  are described below. In step  301 ′, FA  216  adds the GFA address into the HFAIP extension, constructs message  310 ′ which includes FA CoA+HFAIPext, and sends message  310 ′ to MN  262 . This triggers the subsequent signaling described in  FIG. 4 . Next, in step  303 ′, MN  262  issues RREQ message  270   a ′ to FA  216  with a blank CoA as the GFA CoA is not yet assigned. Then, in step  305 ′, FA  216  includes FA CoA in the HFA extension, includes the dynamically assigned GFA in the HFAIP extension, signs both by the FA-GFA shared secret, and sends RREQ message  270   b ′ including HFAIPext+HFAext to GFA  230 . Next, in step  307 ′, GFA  230  replaces FA CoA in HFAext with a dynamically assigned GFA CoA, signs HFAIPext and HFAext with GFA-HA shared secret, and sends RREQ message  270   c ′ including HFAIPext+HFAext to HA  240 . Upon reception of message  270   c ′, the process  130  is triggered at the HA  240  towards the GFA  230 . Additionally, the HA  240  extracts GFA and GFA CoA from message  270   c ′, signs them with the HA-MN shared secret, and sends them toward the MN  262  in the RREP message  271   a ′ including HFAIPext+HFAext to GFA  230 . GFA  230 , in step  311 ′ forwards GFA and GFA CoA towards MN  262  via RREP message  271   b ′ including HFAIPext+HFAext to FA  216 . Next, FA  216 , in step  313 ′, forwards the GFA and GFA CoA to MN  262  via Message  271   c ′ including HFAIPext+HFAext. Finally, in step  315 ′, MN  262  retrieves GFA address for use in the HA field of the Regional Registration, and the GFA CoA for use as the CoA in Registration Requests to the HA. 
       FIG. 5  illustrates the additional processing associated with a dynamically assigned FA CoA and a dynamically assigned HA. 
       FIG. 5  repeats the elements ( 262 ,  216 ,  230 ,  240 ) of  FIG. 3 .  FIG. 5  includes 3 addressing domains: an addressing domain 1  5201 , an addressing domain 2  5203 , and an addressing domain 3  5207 . A boundary line  5205  separates domain 1  5201  from domain 2  5203 . A boundary line  5206  separates domain 1  5201  from domain 3  5207 . MN  262  is in addressing domain 3  5207 . FA  216  is located on the boundary  5206  between addressing domain 3  5207  and addressing domain 1  5201 . GFA  230  is located on the other boundary  5205  separating addressing domain 1  5201  from addressing domain 2  5203 . HA  240  is located in addressing domain 2  5203 . Steps ( 501 ,  503 ,  505 ,  507 ,  509 ,  511 ,  513 ,  515 ) of  FIG. 5  are similar to the steps ( 301 ,  303 ,  305 ,  307 ,  309 ,  311 ,  313 ,  315 ) of  FIG. 3 , respectively. Messages ( 310 ″,  270   a ″,  270   b ″,  270   c ″,  271   a ″,  271   b ″,  271   c ″) of  FIG. 5  are similar to messages ( 310 ,  270   a ,  270   b ,  270   c ,  271   a ,  271   b ,  271   c ) of  FIG. 3 , respectively. 
       FIG. 5  shows two additional novel aspects of the invention: the dynamic allocation of a HA  240  and the case of the FA  216  straddling two addressing domains. Dynamic HA allocation is, without loss of generality, undertaken at the FA  216  potentially in conjunction with a policy server. The allocated HA address is then able to be used in selecting the GFA  230  address and the GFA CoA  104   b  as part of the same allocation procedure. If however the HA allocation is undertaken at the GFA  230  then only the GFA CoA  104   b  can be dynamically allocated based on the HA address  240  because of the GFA  230  will have be allocated at the FA  216  without knowledge of the yet to be assigned HA  240 . Assuming the HA address is allocated at the FA  216 , and having established the GFA  230 , then the FA  216  needs to pass to the GFA  230  in message  270   b ″ the HA address in the Home Agent IP Address extension (HAIPext), or in a HFAIPext which includes flags or other indicators to differentiate between different types of addresses. The GFA  230  on receiving this HA address is then able to direct message  270   c ″ to that identified HA address. The HA address is already returned to the MN  262  in the standard MIP RREP so the HAIPext is not needed to be included in messages  271 ″. 
     The second aspect of  FIG. 5  is the addition of addressing domain 3  5207  between the MN  262  and the FA  216 , such that the address included in message  310 ″ is now the FA address from domain 3  5207 , and the FA  216  must then dynamically allocate a FA CoA from domain 1  5201  for inclusion in message  270   b ″ to facilitate the building of a MIP tunnel between the GFA  230  and the FA CoA at FA  216 . This is a second example of the applicability of  FIG. 1 , where the MN  262  is the downstream node  102 , the GFA  230  is the upstream node  106 , and the FA  216  is the intermediate node  104  with FA address  104   a ′ from domain 3 and FA CoA  104   b ′ from domain 1  5201 . Process  130  is then the tunnel construction between the GFA  230  and the FA  216 . 
     The steps and signaling of  FIG. 5  are described below. In step  501 , for movement detection purposes, FA  216  advertises to MN  262  the FA address from domain 3  5207  and the GFA address from domain 1  5201  via FAA message  310 ″ including FA+GFA address. The subsequent messaging of  FIG. 5  is triggered when the MN  262  receives message  310 ″ from FA  216 . In step  503 , MN  262  issues RREQ message  270   a ″ to FA  216  with a blank CoA field because the GFA CoA is not yet known. Next, in step  505 , FA  216  dynamically assigns from domain 1  5201 , potentially with AAA support, a FA CoA to the MN  262 , and dynamically assigns from domain 2  5203 , potentially with AAA support, a HA  240  to the MN  262 . Then, FA  216  sends RREQ message  270   b ″ including HA address in HAIPext to GFA  230 . Upon reception of message  230 , in step  507 , GFA  230  forwards the RREQ to HA  240  in RREQ message  270   c ″. In step  509 , HA  240  sends RREP message  271   a ″ to GFA  230  so that the MN  262  can ultimately learn the HA address from the RREP. Proceeding to step  511 , GFA  230  forwards RREP via message  271   b ″ to FA  216 . Then, in step  513 , FA  216  signs with an MN-FA shared secret, and then returns the dynamically assigned FA CoA to the MN  262  via RREP message  271   c ″ including FA CoA in HFAext. Finally, in step  515 , MN  262  retrieves from RREP message  271   c ″ the FA CoA for use in the CoA field of Regional Registration and the HA address for use in subsequent RREQ messages to the HA  240 . 
     In various embodiments nodes described herein are implemented using one or more modules to perform the steps corresponding to one or more methods of the present invention, for example, signal processing, message generation and/or transmission steps. Thus, in some embodiments various features of the present invention are implemented using modules. Such modules may be implemented using software, hardware or a combination of software and hardware. Many of the above described methods or method steps can be implemented using machine executable instructions, such as software, included in a machine readable medium such as a memory device, e.g., RAM, floppy disk, etc. to control a machine, e.g., general purpose computer with or without additional hardware, to implement all or portions of the above described methods, e.g., in one or more nodes. Accordingly, among other things, the present invention is directed to machine-readable medium including machine executable instructions for causing a machine, e.g., processor and associated hardware, to perform one or more of the steps of the above-described method(s). 
     Numerous additional variations on the methods and apparatus of the present invention described above will be apparent to those skilled in the art in view of the above description of the invention. Such variations are to be considered within the scope of the invention. The methods and apparatus of the present invention may be, and in various embodiments are, used with CDMA, orthogonal frequency division multiplexing (OFDM), and/or various other types of communications techniques which may be used to provide wireless communications links between access nodes and mobile nodes. In some embodiments the access nodes are implemented as base stations which establish communications links with mobile nodes using OFDM and/or CDMA. In various embodiments the mobile nodes are implemented as notebook computers, personal data assistants (PDAs), or other portable devices including receiver/transmitter circuits and logic and/or routines, for implementing the methods of the present invention. 
     The above described methods and apparatus are exemplary. Numerous variations are possible while keeping within the scope of the invention.