Abstract:
A tunnel setup protocol enables tunnel clients to set up IPv6-in-IPv4 networks to permit IPv6 nodes to communicate across the IPv4 network using IPv6 native packets. The tunnel setup protocol uses a control channel to negotiate tunnel configuration parameters and exchange tunnel configuration data between a tunnel client and a tunnel broker server. The tunnel setup is automatic, and migration to IPv6 is ameliorated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This is the first application filed for the present invention.  
         MICROFICHE APPENDIX  
         [0002]    Not Applicable.  
         TECHNICAL FIELD  
         [0003]    The invention relates in general to the transition of Internet Protocol (IP) networks from IP version 4 (IPv4) to IP version 6 (IPv6) and, in particular, to a method and apparatus for connecting IPv6 devices through an IPv4 network using a tunnel setup protocol.  
         BACKGROUND OF THE INVENTION  
         [0004]    Internet Protocol (IP) was created in the 1960&#39;s by the United States Advanced Research Projects Agency (ARPA). The Agency&#39;s mission was to create instruments useful for military purposes, in particular communications and decentralized computer networks. The original idea was to create connections between military bases using a decentralized communications network with a mesh structure that would permit network function despite significant damage to the country&#39;s infrastructure sustained in a military attack. In the early years of its development, the Internet was used for data transfers, principally as file transfer protocol (FTP) sessions.  
           [0005]    Use of the Internet spread from the military to the scientific and educational communities in the  1970 &#39;s and 80&#39;s. Propagation of the Internet was, however, slow until the Worldwide Web (WWW) was created. The Worldwide Web was first intended to provide a convenient channel for the transfer of scientific information. However, it caught the attention of the commercial world and in the 1990&#39;s an explosive growth of the expansion of the Internet ensued. That explosive growth continues today. The current Internet uses an Internet Protocol referred to as IP version 4 (IPv4). IPv4 uses address fields that are 32 bits long. Although the potential number of IP addresses is 2 32 , over 70% of those addresses have already been assigned and, if as expected the explosive growth of the Internet continues at its current pace, total exhaustion of IPv4 addresses will occur by 2006. Consequently, the Internet Engineering Task Force (IETF) has developed a new Internet standard referred to as IPv6 which uses 128-bit addressing. The address space in IPv6 is intended to accommodate connection of substantially any intelligent electronic device to the IP network. This includes mobile devices.  
           [0006]    It is well known that IPv4 and IPv6 are not compatible because of the differences in address space. Consequently, IPv4 and IPv6 networks can only be interconnected by gateway nodes provisioned with both IPv4 and IPv6 network stacks. However, because of the current lack of available IPv4 address space, IPv6 networks are being deployed and connected to the IPv4 network. A need has therefore arisen for equipment and methods to permit IPv6 devices to communicate across the IPv4 network in order to enhance IPv6 device interconnectivity. It is also well known that a data encapsulation technique known as tunneling can be used for transferring IPv6 packets across the IPv4 network. When an IPv6-in-IPv4 tunnel is created, IPv6 packets are encapsulated with IPv4 headers that are used to transfer the packets through the IPv4 network to a predetermined IPv4-IPv6 host or gateway. The establishment of IPv6-in-IPv4 tunnels is a complex process. Traditionally, the tunnels have been constructed using a manual process for setting up tunnel endpoints at edges of the IPv4 network. This is a time-consuming task that requires a considerable level of expertise and experience. Consequently, manual establishment of tunnels is unworkable with mobile devices and beyond the expertise of a majority of users.  
           [0007]    Many known IPv6 transition techniques use tunneling to overlay an IPv6 network over an IPv4 network. Some of these techniques are manual, some are automated. RFC1933 entitled “Transition Mechanisms for IPv6 Hosts and Routers” (April 1996), describes how to encapsulate IPv6 packets in IPv4 packets. It also describes how to manually configure an IPv6-in-IPv4 tunnel. However, this is a completely manual process and is therefore not scalable.  
           [0008]    An automated technique referred to as “6to4”, is described in RFC3056 entitled “Connection of IPv6 Domains via IPv4 Clouds” (February 2001), which specifies an optional interim mechanism for IPv6 sites to communicate with each other over the IPv4 network without explicit tunnel setup, and for them to communicate with native IPv6 domains via relay routers. Effectively it treats the wide area IPv4 network as a unicast point-to-point link layer. The mechanism is intended as a start-up transition tool used during the period of co-existence of IPv4 and IPv6. It is not intended as a permanent solution. The document defines a method for assigning an interim unique IPv6 address prefix to any site that currently has at least one globally unique IPv4 address, and specifies an encapsulation mechanism for transmitting IPv6 packets using such a prefix over the global IPv4 network. The motivation for this method is to allow isolated IPv6 domains or hosts, attached to an IPv4 network which has no native IPv6 support, to communicate with other such IPv6 domains or hosts with minimal manual configuration, before they can obtain native IPv6 connectivity. It incidentally provides an interim globally unique IPv6 address prefix to any site with at least one globally unique IPv4 address, even if combined with an IPv4 Network Address Translator (NAT).  
           [0009]    Another automated technique referred to as “6over4” is described in RFC2529, which is entitled “Transmission of IPv6 over IPv4 Domains without Explicit Tunnels” (March 1999). In accordance with this technique, the IPv4 address of the destination endpoint is embedded in the prefix part of the IPv6 destination address. This allows isolated IPv6 hosts, located on a physical link which has no directly connected IPv6 router, to become fully functional IPv6 hosts by using an IPv4 multicast domain as their virtual local link. Thus, at least one IPv6 router using the same method must be connected to the same IPv4 domain if IPv6 routing to other links is required. This is therefore a host-to-network or a network-to-network mechanism.  
           [0010]    Internet draft IETF-ngtrans-isatap dated Apr. 18, 2002 and entitled “Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)” specifies a protocol that connects IPv6 hosts and routers (nodes) within IPv4 sites. ISATAP is a transition mechanism that enables incremental deployment of IPv6 by treating the site&#39;s IPv4 infrastructure as a Non-Broadcast Multiple Access (NBMA) link layer for IPv6. ISATAP mechanisms use an IPv6 interface identifier format that embeds an IPv4 address—this enables automatic IPv6-in-IPv4 tunneling within a site, whether the site uses globally assigned or private IPv4 addresses. The interface identifier format can be used with both local and global unicast IPv6 prefixes—this enables IPv6 routing both locally and globally. ISATAP mechanisms introduce no impact on routing table size and require no special IPv4 services (e.g., IPv4 multicast).  
           [0011]    A semi-automatic establishment of IPv6-in-IPv4 tunnels is described in RFC3053 entitled “IPv6 Tunnel Broker” (January 2001). The tunnel broker described in this document is a worldwide web implementation that permits end-users to select a pre-configured IPV6-in-IPv4 tunnel. However, the system does not support any real negotiation between the end-user and the tunnel broker. If end-users use dynamic IPv4 addresses, a manual operation must be done to update the tunnel broker. This limits the scalability of deploying IPv6 networks, and introduces a considerable onus on inexperienced users.  
           [0012]    Consequently, there exists a need for a method and apparatus for automating and simplifying the establishment of IPv6-in-IPv4 tunnels to facilitate adoption and use of IPv6, as well as to ameliorate the transition from IPv4 to IPv6.  
         SUMMARY OF THE INVENTION  
         [0013]    It is therefore an object of the invention to provide a tunnel setup protocol for automating the establishment of IPv6-in-IPv4 tunnels through the IPv4 network.  
           [0014]    It is a further object of the invention to provide a tunnel setup protocol that is suitable for use with mobile devices, to facilitate a transition from IPv4 to IPv6.  
           [0015]    The invention provides a tunnel setup protocol that facilitates a transition from IPv4 to IPv6 by permitting IPv6 devices to communicate across the IPv4 network. In accordance with the invention, a control channel is established between a tunnel client and a tunnel broker server. The control channel established between the tunnel client and the tunnel broker server is used to exchange tunnel configuration information and, optionally, to negotiate configuration parameters for the IPv6-in-IPv4 tunnel. After the tunnel configuration parameters have been established, the tunnel broker server configures a tunnel broker server endpoint. The tunnel broker server endpoint may be supported by the tunnel broker server, or by another gateway node, such as an IPv4/IPv6 router connected to both the IPv4 and the IPv6 networks.  
           [0016]    The tunnel client also configures a tunnel endpoint, referred to as the tunnel client endpoint for the IPv6-in-IPv4 tunnel. The tunnel client endpoint may likewise be configured on the tunnel client, or another IPv4/IPv6 node, such as a gateway router. In order to improve capacity, either the tunnel client or the tunnel broker server may have a list of nodes that support tunnel endpoints so that traffic loads can be distributed to improve throughput. The invention therefore permits the automated establishment of IPv6-in-IPv4 tunnels using a control channel. The use of the control channel enables the automated negotiation of specific configuration details, such as IPv6 prefix length, DNS delegation and router peering protocol. This facilitates the deployment of IPv6 networks and ameliorates the transition from IPv4 to IPv6. The invention is particularly useful in mobile devices since new IPv6-in-IPv4 tunnels can be rapidly and automatically configured to permit true, unencumbered mobility of those devices, thus enhancing the attraction of deploying IPv6. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:  
         [0018]    [0018]FIG. 1 is a schematic diagram of a point-to-point (PPP) data connection over a dial-up link between a computer and a network access server;  
         [0019]    [0019]FIG. 2 is a schematic diagram of a connection between an IPv4/IPv6 node and an IPv6 network implemented in accordance with the invention;  
         [0020]    [0020]FIGS. 3 a - 3   d  are a flow chart of a method for connecting IPv6 devices through an IPv4 network using a tunnel setup protocol;  
         [0021]    [0021]FIG. 4 is a connection progress diagram of the establishment of an IPv6-in-IPv4 tunnel between a tunnel client and a tunnel broker server, and subsequent use of the tunnel by IPv6 nodes connected to respective IPv6 networks;  
         [0022]    [0022]FIG. 5 is a connection progress diagram of another implementation of the invention in which a tunnel client connects to a tunnel broker server and establishes an IPv6-in-IPv4 tunnel for the purposes of communicating with an IPv6 node in an IPv6 network;  
         [0023]    [0023]FIG. 6 is a connection progress diagram illustrating the establishment of an IPv6-in-IPv4 network in which the tunnel broker server configures a remote router as the tunnel endpoint for the IPv6-in-IPv4 tunnel;  
         [0024]    [0024]FIG. 7 is a connection progress diagram illustrating a method in accordance with the invention in which a tunnel client configures a remote router as the tunnel endpoint for an IPv6-in-IPv4 tunnel used to permit communication between IPv6 nodes in respective IPv6 networks;  
         [0025]    [0025]FIG. 8 is a connection progress diagram showing an implementation of the invention in which both the tunnel client and the tunnel broker server configure remote routers to serve as tunnel endpoints for an IPv6-in-IPv4 tunnel; and  
         [0026]    [0026]FIG. 9 is a connection progress diagram illustrating the establishment of IPv6-in-IPv4 tunnels by a mobile tunnel client. 
     
    
       [0027]    It will be noted that throughout the appended drawings, like features are identified by like reference numerals.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    The invention provides a method and apparatus for connecting IPv6 devices through an IPv4 network using a tunnel setup protocol (TSP), as described in Applicant&#39;s Internet-Drafts, a first of which bears a date of June 2001 and was published on Jul. 18, 2001 and is entitled “Tunnel Setup Protocol (TSP) draft-vg-ngtrans-tsp-00”, and the second of which bears a date of Jul. 13, 2001 and was published on Jul. 18, 2001, entitled “IPv6 over IPv4 profile for Tunnel Setup Protocol (TSP) draft-vg-ngtrans-tsp-v6v4profile-00”, each of which is respectively incorporated herein by reference.  
         [0029]    In accordance with the invention, a control channel is established between a tunnel client and a tunnel broker server. Both the tunnel client and the tunnel broker server must be connected to the IPv4 network. The control channel established between the tunnel client and the tunnel broker server is used to negotiate configuration parameters for an IPv6-in-IPv4 tunnel. After the configuration parameters are established, the tunnel broker server configures a tunnel broker server endpoint and the tunnel client configures a tunnel client endpoint for the IPv6-in-IPv4 tunnel. The respective tunnel endpoints may be configured on the respective tunnel client and tunnel broker server. Alternatively, either of the tunnel client and the tunnel broker server may configure remote tunnel endpoints. In order to improve capacity, either the tunnel client or the tunnel broker server may have a list of nodes that support tunnel endpoints so that traffic loads can be distributed to improve throughput. The invention therefore permits the automated establishment of IPv6-in-IPv4 tunnels, which facilitates the deployment of IPv6 networks and ameliorates the transition from IPv4 to IPv6.  
         [0030]    [0030]FIG. 1 is a schematic diagram of a point-to-point (PPP) dial-up connection between a client computer  20  and a network access server  22  to provide access to an IPv4 network  24  in a manner well known in the art. As is well understood, a PPP-control channel  26  is established over the dial-up connection between the client computer  20  and the network access server  22 . The dial-up connection passes through a modem  30 , a switched telephone network  32  and a modem bank  34  in a manner well known in the art. The PPP control channel  26  shares the dial-up connection with a PPP data channel  28 , which is used to send IPv4 data packets from the client computer  20  to one or more selected hosts in the IPv4 network  24 .  
         [0031]    [0031]FIG. 2 is a schematic diagram illustrating one implementation of a system provisioned with a tunnel setup protocol in accordance with the invention. In accordance with the invention, a control channel  40  is established through the IPv4 network  24  between a tunnel client  50  and a tunnel broker server  60  using a transfer control protocol (TCP) messaging. The control channel  40  is used to negotiate parameters for establishing an IPv6-in-IPv4 tunnel through the IPv4 network  24 . The tunnel is used to establish a data channel  42  which extends between first and second tunnel endpoints. In this example, the tunnel endpoints are the tunnel client  50  and the tunnel broker server  60 . The data channel is used to transfer IPv6 data packets through the IPv4 network. The IPv6 data packets are encapsulated at the opposite endpoints of the IPv6-in-IPv4 tunnel, as will be explained below in more detail.  
         [0032]    [0032]FIGS. 3 a - 3   d  are a flow diagram illustrating the tunnel setup protocol in accordance with the invention. The process begins in step  100  when a tunnel setup protocol (TP) client, hereinafter referred to as a tunnel client  50  (FIG. 2) connects to a tunnel broker server (TB)  60  using TCP, as explained above. Alternatively, the tunnel client  50  may use User Datagram Protocol (UDP) messaging to establish the control channel  40 . After the control channel  40  is established, the tunnel client sends the version of the TSP that it supports using the control channel  40  to the tunnel broker server  60  (step  102 ). On receipt of the TPS protocol version, the tunnel broker server  60  determines whether it supports the same version of the tunnel setup protocol (step  104 ). If it is not provisioned to support the tunnel client&#39;s version of the tunnel setup protocol, the tunnel broker server  60  returns an error message via the control channel  40  (step  106 ) and branches to connector C (see FIG. 3 d ) where the tunnel broker server  60  determines whether it has an alternate list of tunnel broker servers that it can provide to the tunnel client (as will be explained below in more detail). If the tunnel broker server  60  does support the tunnel client&#39;s version of the tunnel setup protocol, the tunnel broker server  60  returns a list of its capabilities (step  108 ) to the tunnel client  50  over the control channel  40 . The capabilities of the tunnel broker server  60  include, for example, authentication mechanisms, types of tunnel supported, lengths of IPv6 prefixes that can be assigned, as well as Domain Name Service (DNS) delegation supported, and router peering protocols supported, etc.  
         [0033]    In step  110 , the tunnel client  50  determines whether the capabilities of the tunnel broker server  60  are satisfactory for the purposes it requires. If not, the tunnel client  50  closes the tunnel setup protocol session (step  112 ) and the process ends. Otherwise, the tunnel client  50  selects an authentication mechanism from the list supported by the tunnel broker server  60  and specifies the authentication mechanism in an authentication message sent via the control channel  40  to the tunnel broker server  60  (step  114 ). Subsequently, the tunnel broker server  60  and the tunnel client  50  exchange authentication data (step  116 ) via the control channel  40 . In step  118 , the tunnel broker server  60  verifies the tunnel client authentication data.  
         [0034]    As shown in FIG. 3 b,  after verifying the tunnel client authentication data, the tunnel broker server  60  determines whether the tunnel client  50  is authorized to establish the tunnel (step  120 ). If the tunnel client  50  is not authorized to establish the tunnel, the tunnel broker server  60  returns an error message via the control channel  40  and closes the session (step  122 ). If the tunnel client  50  is authorized to establish the tunnel, the tunnel broker server  60  returns an authentication successful message (step  124 ) to the tunnel client  50 . The tunnel client  50  then sends a tunnel request message via the control channel  40  (step  126 ) to the tunnel broker server  60 . The tunnel request message may include requests for an IPv6 prefix, a DNS delegation, router peering, etc., as will be explained below in more detail. On receipt of the tunnel request message, the tunnel broker server  60  determines whether it is provisioned to offer the service as requested (step  128 ). If not, the tunnel broker server  60  determines (step  130 ) whether it is provisioned to offer a similar service. If not, the tunnel broker server  60  returns an error message via the control channel  40  and branches to step C, where it determines in step  178  (see FIG. 3 d ) if it is provisioned with a list of alternate tunnel broker servers. If not, it closes the session (step  180 ). If so, it returns the list via the control channel  40  to the tunnel client  50  to permit the tunnel client  50  to attempt the establishment of an IPv6-in-IPv4 tunnel using another tunnel broker.  
         [0035]    If the tunnel broker is provisioned to provide the requested service or a similar service as determined in steps  128 ,  130 , the tunnel broker server  60  assigns an IPv4-in-IPv6 tunnel to the tunnel client. The tunnel broker may also assign an IPv6 prefix in a manner well known in the art, provide domain name service (DNS) delegation, as will be explained below in more detail, and router peering to the tunnel client  50 , as appropriate (step  134 ).  
         [0036]    In step  136 , the tunnel broker server  60  determines whether DNS delegation has been requested. If so, the tunnel broker server  60  configures its DNS servers for the DNS delegation by writing the tunnel client&#39;s DNS server addresses to DNS servers associated with the tunnel broker server  60 , to point to the tunnel client&#39;s DNS servers for name space associated with the assigned IPv6 prefix (step  138 ). If DNS delegation is not requested, the tunnel broker server  60  configures its DNS servers with an “A record” (step  140 ) for the client tunnel endpoint address, in a manner known in the art. In step  142  (FIG. 3 c ), the tunnel broker server  60  selects and configures a tunnel endpoint for the tunnel it assigned in step  134 . The configuration of the tunnel endpoint includes configuring router peering. The tunnel broker then awaits confirmation that the tunnel endpoint configuration was successful (step  144 ). If the configuration was not successful, the tunnel broker server  60  determines in step  146  whether another tunnel endpoint is available by, for example, consulting a table of tunnel endpoints stored in the tunnel broker server memory (step  146 ). If another tunnel endpoint is not available, or all tunnel endpoints are at capacity, the tunnel broker server  60  sends an error message over the control channel (step  148 ) to the tunnel client  50  and branches to steps  178 - 180 , as explained above.  
         [0037]    If the tunnel endpoint configuration is determined to be successful in step  144 , the tunnel broker server  60  sends the tunnel configuration parameters along with any required IPv6 prefix, DNS information, router peering information, etc. to the tunnel client  50  using the control channel  40 , along with a success code (step  150 ). On receipt of this information, the tunnel client determines whether it will accept the tunnel configuration (step  152 ). If it does not find the tunnel configuration acceptable, the tunnel client determines (step  154 ) whether it will negotiate a different configuration. It should be noted that the tunnel client may be implemented with or without the capacity for parameter negotiation. If it is not equipped for negotiation or decides to terminate negotiation, the process moves to step  156 , in which the client refuses the tunnel configuration and advises the tunnel broker  60  by sending a refusal message over the control channel  40  (step  156 ). On receipt of the refusal message, the tunnel broker server  60  rolls back the configuration of the tunnel endpoint, the DNS configurations, etc. (step  158 ) and branches to steps  178 - 180 , as explained above.  
         [0038]    If the client determines in step  154  that it will negotiate the tunnel configuration, it may, for example, assess whether negotiation should proceed by comparing a negotiation count with a predetermined threshold (step  160 ). If the negotiation count is greater than the threshold, the process branches to steps  156 ,  158  and  178 - 180 , as explained above. Otherwise, the negotiation counter is incremented (step  162 ) and the tunnel client  50  returns via the control channel  40  a revised parameter list to the tunnel broker server  60  and the process branches back to step  128 .  
         [0039]    If the tunnel client accepts the tunnel configuration in step  152 , the tunnel client  50  configures its tunnel endpoint and, if required, configures its DNS server(s) as explained above, and router peering in its tunnel endpoint, if required (step  166 ). The tunnel is thus established and IPv6 traffic can be sent over the established tunnel (step  168 ). The tunnel client  50  then determines whether it wants to keep the tunnel setup protocol session alive (step  170 ). If so, the tunnel client  50  sends a keep-alive message to the tunnel broker server  60  via the control channel  40  (step  172 ) and after a predetermined time delay (step  174 ) repeats steps  170 ,  172 . If the tunnel client  50  does not wish to keep the tunnel setup protocol session alive, the tunnel client  50  closes the tunnel setup protocol session by dropping the control channel  40  (step  176 ). The tunnel established between the tunnel endpoints continues, however, for a period determined by the tunnel broker server  60 , or through negotiation with the tunnel client  50 , for a predetermined period of time, as will be explained below with reference to FIGS. 4 and 5.  
         [0040]    [0040]FIG. 4 is a connection progression diagram illustrating an exemplary implementation of the, tunnel setup protocol in accordance with the invention. In this example, an IPv6-in-IPv4 tunnel is established between a tunnel client  50  and a tunnel broker server  60 , which respectively serve as endpoints for the tunnel. The tunnel client  50  is a router that is connected to an IPv6 network  70   a  and the IPv4 network  24 . Consequently, the tunnel client  50  is provisioned with an IPv4 stack as well as an IPv6 stack and is further provisioned to encapsulate IPv6 packets in IPv4 packets, as well as to decapsulate IPv6 packets encapsulated in IPv4 packets, to permit IPv6 traffic to pass through the tunnel. The tunnel broker server  60  is likewise connected to both the IPv4 network  24  and the IPv6 network  70  and provisioned with the same stacks and data encapsulation/decapsulation capability.  
         [0041]    As shown in the diagram, in step  200 , the router is configured as a tunnel client  50 . Once configured as a tunnel client  50  so that it knows how to contact the tunnel broker server  60 , the router is provisioned to establish a control channel  40  to the tunnel broker server  60 , as explained above. Subsequently, in step  202 , the tunnel client  50  sends a connect message to the tunnel broker server  60  to establish the control channel  40 . The tunnel client  50  may be prompted to establish the control channel for any number of reasons. For example, the tunnel client  50  is prompted to establish the control channel when the IPv6 node  72  generates IPv6 traffic addressed to an IPv6 node in a different IPv6 network, on reboot, on re-establishing IPv4 re-connectivity, etc. On receipt of the connect message, the tunnel broker server  60  returns an acknowledgement message (step  204 ) and the control channel  40  is established. The tunnel client  50  then sends the version of the tunnel setup protocol it supports to the tunnel broker server  60  (step  206 ) via the control channel  40 . The tunnel broker server  60  returns, via the control channel  40 , a list of the tunnel setup functions it supports (step  208 ). The tunnel client  50  selects an authentication mechanism and authentication information is exchanged (step  210 ). In step  212 , the tunnel broker server  60  determines that the tunnel client  50  is authorized for the service and returns an authorization successful message (step  214 ). On receipt of the message, the tunnel client  50  formulates a tunnel request message which it sends to the tunnel broker server  60  in step  216 . The request, as explained above, optionally includes a request for an IPv6 prefix, DNS delegation, and a router peering. On receipt of the request, the tunnel broker  60 , in this example, is provisioned to satisfy the request and configures a tunnel endpoint (step  218 ) to serve the request.  
         [0042]    The tunnel broker server  60  then returns a tunnel answer message (step  220 ) which includes tunnel configuration parameters, including IPv4 and IPv6 addresses for both the tunnel broker server and the tunnel client endpoints as well as any other information requested by the tunnel client  50  in step  216 . On receipt of the tunnel answer message, the tunnel client configures its tunnel endpoint (step  222 ). Thereafter, the tunnel client  50  may optionally send keep-alive messages (step  224 ), as explained above, to keep control channel  40  open. The tunnel client may also optionally terminate the tunnel protocol session (step  226 ) at any time. After step  220  is complete, the tunnel is established and data packets can flow between the IPv6 node  72  and the IPv6 node  74 , as shown in steps  228 - 240 .  
         [0043]    Included in the information sent by the tunnel broker server  60  in the tunnel answer (step  220 ), was a tunnel lifetime parameter, which specifies a duration of the IPv6-in-IPv4 tunnel. When the tunnel lifetime expires (step  242 ), the tunnel broker server  60  deconstructs the tunnel endpoint, DNS delegation and router peering so that traffic can no longer pass through the tunnel, as explained below with reference to FIG. 5.  
         [0044]    [0044]FIG. 5 is a connection progression diagram that further explains the process in accordance with the invention. In this example, the tunnel setup protocol client  50  is an IPv4/6 node that serves as a tunnel endpoint. In step  250 , the tunnel protocol session parts I and II are performed as described above with reference to FIG. 4. In step  252 , the tunnel client  50  starts an IP session by constructing an IPv6 packet and encapsulating the IPv6 packet in an IPv4 packet in a manner known in the art. The IPv6 packet is sent in step  254  through the tunnel to the tunnel broker server  60 . The tunnel broker server  60  decapsulates the IPv6 packet (step  256 ) and forwards it in IPv6 native format to the IPv6 node  74  (step  258 ). The IPv6 node  74  returns an IPv6 packet in IPv6 native format (step  260 ). The packet is encapsulated in an IPv4 packet by the tunnel broker server  60  (step  262 ) and forwarded through the tunnel in step  264 . In step  268 , the tunnel lifetime expires and the tunnel endpoint is deconstructed, as explained above. Thereafter, when the IPv6 node  74  sends an IPv6 packet in native format (step  270 ), the tunnel broker returns a destination unreachable packet (step  272 ) in a manner known in the art.  
         [0045]    [0045]FIG. 6 is a connection progression diagram that illustrates the re-establishment of a tunnel using a tunnel setup protocol session prior to the expiry of a tunnel being used by the tunnel client. In this example, the tunnel broker server  60  configures a remote tunnel endpoint which is a router  76  connected between the IPv4 network  24  and the IPv6 network  70 b. In step  280 , the tunnel setup protocol session (part I) is conducted between the tunnel client  50  and the tunnel broker server  60 , as explained above with reference to FIG. 4. After the tunnel broker server  60  receives the tunnel request message from the tunnel client  50 , the tunnel broker server  60  configures a remote router  76  as the tunnel endpoint (step  282 ) and, the tunnel session concludes with the part II procedures described above (step  284 ). Thereafter, IPv6 node  72  connected to IPv6 network  70   a  sends IPv6 packets through the tunnel (steps  286 - 290 ) to IPv6 node  74 . Meanwhile, the tunnel client  50  monitors the lifetime of the tunnel established with the tunnel broker server  60  and, when the IPv6-in-IPv4 tunnel is about to expire, as shown at step  292 , the tunnel client  50  re-initiates tunnel setup protocol sessions parts I and II to re-establish the tunnel through the IPv4 network (step  294 ). It should be noted that the tunnel broker server  60  may route to a different tunnel endpoint to preserve service balancing. A tunnel broker server  60  configured as a host can serve multiple tunnel endpoints to enable and facilitate service balancing, etc. In that case, the tunnel endpoints are normally configured as routers  76  connected to both the IPv4 network  24  and the IPv6 network  70 . As also explained above, such routers are provisioned with both IPv4 and IPv6 stacks as well as encapsulation/decapsulation capability.  
         [0046]    [0046]FIG. 7 illustrates yet another potential configuration of a system in accordance with the invention in which the tunnel client  50  is configured as a host adapted to configure one or more remote tunnel endpoints in the same way that the tunnel broker server  60  configures remote tunnel endpoints as explained above. In step  300 , the tunnel setup protocol sessions parts I and II are performed to the point that the tunnel client configures the tunnel endpoint (step  300 ). In step  302 , the tunnel client  50  configures the remote tunnel endpoint at a router  78  selected, for example, from a table of available tunnel endpoint routers that serve as gateways to the IPv6 network  70   a.  In order to configure the tunnel endpoint, the tunnel client  50  sends the IPv4 and IPv6 addresses of the tunnel endpoint  78  and the tunnel endpoint configured at the tunnel broker server  60 . Thereafter, the IPv6 node  72  is enabled to communicate with IPv6 node  74  using IPv6 native packets which are encapsulated, as explained above, and moved through the IPv4 network  24  (steps  304 - 308 ) using the tunnel established in steps  300 ,  302 .  
         [0047]    [0047]FIG. 8 is a connection progression diagram illustrating yet another implementation of the system in accordance with the invention in which both the tunnel client  50  and the tunnel broker server  60  configure remote tunnel endpoints. In this embodiment, the tunnel client  50  initiates and conducts a tunnel setup protocol session (step  310 ). As part of the tunnel setup protocol session, a tunnel broker server  60  configures a remote gateway router  80  to serve as a tunnel endpoint (step  312 ), as described above. The tunnel client  50  likewise configures a remote gateway router  78  to serve as a tunnel endpoint (step  314 ). Thereafter, the IPv6 node  72  is enabled to send IPv6 packets in native format to the IPv6 node  74  (steps  316 - 320 ), and vice versa.  
         [0048]    [0048]FIG. 9 is a connection progression diagram that illustrates yet another implementation of the system in accordance with the invention. In this example, the tunnel client  50  is a mobile device, such as a cellular telephone, a personal data assistant (PDA) or a laptop computer, which serves as a router in an IPv6 subnetwork. As illustrated, the mobile device in a first location functions as a tunnel client  50   a  having an IPv4 address  1 . In the first location, the mobile tunnel client  50   a  commences and performs a tunnel setup protocol session with the tunnel broker (step  330 ) and in the course of the tunnel setup protocol session receives an IPv6 prefix from the tunnel broker server  60 . In this example, the prefix received is “3ffe:1:1::/48. As is well known in the art, this prefix is known as a “/48” prefix which permits the tunnel client router to assign session addresses to IPv6 devices in the domain it controls, in a manner well known in the art. After the tunnel is established in step  330 , the IPv6 node  72  is enabled to communicate with the IPv6 node  74  (steps  332 - 336 ) by sending and receiving IPv6 packets in native format. Subsequently, the mobile tunnel client  50  moves to location  50   b  and its service provider in the IPv4 network assigns a new IPv4 address (ADDR 2). Consequently, a new tunnel must be established. The tunnel client  50   b  therefore initiates and performs the tunnel setup protocol session (step  338 ) with the tunnel broker server  60  and receives the same IPv6 prefix “3ffe:1:1::/48”. Consequently, a new tunnel is established between the mobile tunnel client  50   b  and the tunnel broker server  60  that permits the IPv6 node  72  to again send IPv6 packets in native format to the IPv6 node  74  (steps  340 - 344 ). By receiving the same IPv6 prefix, the IPv6 node keeps its same IPv6 address. Consequently, in the IPv6 realm the mobility of the IPv6 tunnel end point is not perceived.  
         [0049]    The methods and apparatus in accordance with the invention therefore permit mobile devices to automatically establish IPv6-in-IPv4 tunnels through the IPv4 network to permit IPv6 nodes to communicate with other IPv6 nodes in other IPv6 subnetworks. This is of critical importance to the exponentially expanding use of wireless devices and mobile devices in general, and permits seamless networking of such devices.  
         [0050]    The embodiment(s) of the invention described above is(are) intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.