Technical Outlook: analysis of key routing technologies for Mobile IPv6

With the rapid development of Internet technology, to meet the increasing user needs, TCP/IP is gradually evolving from IPv4 to the next generation of Internet protocol IPv6, the Mobile IP Address used as the network layer protocol will provide more comprehensive mobility support for network nodes in IPv6.

Currently, the IETF (InternetEngineeringTaskForce) mobile working group will develop mobile IPv6 standards as the main research topic of the Mobile IP Working Group agenda, and has made a series of progress.

1. Basic Working Mechanism of Mobile IPv6

Based on the advantages of mobile IPv4, mobile IPv6 is designed with many new features in the IPv6 protocol family. The Mobile Ipv6 routing mechanism follows many basic concepts of mobile IIPv4, such as continuing to adopt mobile hosts, home agents, home address, transfer address, home link and foreign link, however, the concept of foreign proxy is no longer used. The routing technology of mobile IPv6 is similar to that of mobile IPV4 in terms of its high-level functions. It has many main functions such as proxy discovery, registration, tunneling, and packet routing. The basic workflow of Mobile IPv6 is as follows:

(1) When the mobile host is re-elected as the home link, the usual IP addressing mechanism is used to select the data packets sent to the mobile host or the data packets sent from the mobile host.

(2) The mobile host uses the router discovery (RouterDiscovery) mechanism of the IPv6 version to determine whether the current location of the mobile host and the link switching between the mobile host.

(3) When a mobile host is moved to a field link, the forwarding address of the field link is obtained through the automatic configuration method defined by mobile IPv6.

(4) The mobile host notifies the home proxy and related communication nodes of the latest forwarding address.

(5) The communication node that knows the forwarding address directly sends data packets to the mobile host, but does not know that the forwarding address sends data packets in the same mechanism as the mobile IPV4 routing mechanism, this means that data packets are first forwarded to the home site proxy and then forwarded to the mobile host through a tunnel.

(6) When a mobile host on a remote link sends a data packet, the mobile host obtains a default router through the ICMPv6 Router Discovery Mechanism and forwards the data packet to the target host through the router.

2 key routing technologies of Mobile IPv6

1. Mobile IPv6 proxy discovery

Mobile IPv6 uses the ICMPv6 Router Discovery Mechanism in the IPv6 neighbor node search function to complete the following functions:

* Determine the current location of the mobile host, whether it is located on the home link or a remote link;

* Determine whether there is link switching for a mobile host;

* The transfer address is obtained when the mobile host moves to a foreign network.

The router discovery mechanism defines two packets: router request and router broadcast. In the router broadcast message, there are three parts: IPv6 Header, ICMPv6 Router broadcast (fixed part), and prefix information, you can determine the current location of the mobile host and perform mobile detection from the optional network prefix domain. The mobile host checks the network prefix in the received broadcast message. If it is the same as the home address prefix of the mobile host, the mobile host is connected to the home network. At this time, the home agent should be notified to have returned to the home link; if no network prefix is the same as that of the home network of the mobile host, the mobile host must be connected to a remote link, in this case, the mobile host determines whether the location of the mobile host is moved by comparing the network prefix in the recently received broadcast message with the previous one.

2. Get the forwarding address

Because Mobile IPv6 does not have the concept of a foreign proxy, mobile hosts can only use the configured forwarding address. A mobile host can obtain the forwarding address in two ways: automatic passive Address Configuration and automatic active address configuration. The Mbit value defined in the broadcast packet of the ICMPv6 Router is used to select the method:

* When M is set to 0, a passive address is automatically configured. The server provides the forwarding address to the mobile host through the IPv6 Configuration protocols DHCPv6 and PPP;

* When M is set to 1, an active IP address is automatically configured to obtain the network prefix of a remote link from the ICMPv6 Router broadcast message, in addition, the mobile host is connected to the interface mark (48-bit physical address or MAC address) of the remote link to form its own forwarding address.

A mobile host can have one or more forwarding addresses at the same time, but only one forwarding address is registered as the "primary forwarding address ".

3. Bind Management

The association between the home address and the transfer address of the mobile host is called a Binding of the mobile host ). Three types of messages are defined in the mobile IPv6 binding Management Mechanism: "Binding Update", "binding approval", and "Binding Request", all of which are placed in the destination optional Header (an extended header of IPv6). These three types of messages are used for communication between the mobile host and the home proxy or communication node, and can also enable the communication node to timely understand and bind the cache to the mobile host's forwarding address.

When a mobile host is configured with a new forwarding address and decides to use this address as its primary forwarding address, the mobile host registers the new binding by sending a "bind update" message to the home agent. The mobile host resends the "bind update" message periodically until the home proxy sends back the Response Message.

The communication node can send a "Binding Request" message to the mobile host. The mobile host is required to send a "Binding Update" message to the mobile host to obtain the current forwarding address of the mobile host and the latest binding of the cache. In the future, the communication node can use the master forwarding address of the mobile host to directly send data packets to the mobile host, instead of being forwarded by the home proxy.

4. Dynamic hometown proxy address discovery

When a mobile host registers a "master forwarding address" with the home agent, it may not know the address of the router that can have the home agent function on the home link. Or, when the mobile host leaves the home link, the original home proxy fails or the router is reconfigured. To this end, the mobile host sends the "ICMP hometown proxy address discovery request" message to the home network. The source address field of the IP Address Header of this packet uses the transfer address of the mobile host. The home agent that receives the request message on the home link will return the "hometown proxy address discovery response" message, and provide its own IP address in the message, in addition, the list of proxy IP addresses of other hometown sites on the home link is also provided.

After receiving the "ICMP hometown proxy address discovery response" message, the mobile host sends the "Binding Update" message to the origin address of the home proxy sending the message for registration. In addition, because the mobile host can obtain the address of another home agent on the home link from the response message, the mobile host will send the "Binding Update" message in the order of the home agent list.

If a home agent on the home link has a valid registration, the mobile host must first register and update the home link agent when registering a new agent. If the registration process fails or is rejected, the mobile host must register with another home agent on the home link. If the mobile host does not know the address of another home agent on the home link, it will implement the "dynamic home proxy address discovery" mechanism.

5. data packet routing

(1) The communication node sends data packets to the mobile host. When the mobile host forwarding address is cached in the communication node, you can use the option in the IPv6 Routing header to directly send data packets to the mobile host. In this case, an optimized path from the source node to the mobile host is used.

When the communication node does not know the forwarding address of the mobile host, the routing data packet method is the same as that of the mobile IPv4, that is, the home proxy intercepts the data packet and sends it to the mobile host through tunneling technology.

(2) The mobile host sends data packets to the communication node. All IPv6 routers have the ICMPv6 Router Discovery Function. When a mobile host is located on a foreign link, you can select one of the router broadcast messages as the default router, configure the corresponding route table, and route the sent packets through the router.

Many vrouters in the network have restrictions on entry filtering rules: packets with incorrect source addresses cannot pass through. When a mobile host sends data packets outside of China, it usually uses the current forwarding address as the source address in the packet header. According to the traditional rules, these data packets will be discarded. Mobile IPv6 defines an additional IPv6 destination option, that is, the "hometown address" option, so that data packets using the forwarding address as the source address of the IPv6 Header will pass normally.

3. Requirements of Mobile IPv6 for IPv6 communication nodes and Routers

As part of the IPv6 protocol stack, the implementation of Mobile IPv6 routing technology puts forward some special requirements for IPv6 communication nodes and Routers:

1. Requirements for IPv6 communication nodes

Each IPv6 node may be a communication node of a mobile host at any time. Each IPv6 node must be able to process the destination option included in the IPv6 packet, that is, the "hometown address" option; each IPv6 node should be able to handle the received "Binding Update" option and return the "binding response" option. Each IPv6 node should be able to bind and manage.

2. Requirements for IPv6 routers

Each IPv6 router supports neighbor node search and ICMPv6 Router Discovery. Each IPv6 router should be able to send "router broadcast messages" at a faster rate "; there should be at least one vro on the home link of the mobile host as its home proxy.

4 Conclusion

This article discusses in depth the basic working mechanism and key routing technology of mobile IPv6. It can be seen that, based on the design experience and many advantages of mobile IPv4, the implementation of Mobile IPv6 utilizes many new ideas and features in the IPv6 protocol family, it has become an integral part of IPv6, providing more comprehensive mobility support for the Internet. The proposal of Mobile IPv6 routing technology also provides new ideas and approaches for the construction of the whole IP network. It has been clearly stipulated in the IMT-2000 standard that the third generation mobile communication system must support mobile IPv6 grouping service. This will promote the deep integration of IP technology and wireless communication technology, that is, the transmission of voice, data, video, images, messages, and other integrated services on the Unified IP communication network platform, truly realizing the integration of voice and data in business, creating incalculable industrial opportunities and business prospects.

Related Articles]

• Prospect Analysis of Mobile IPv6 and operators' Response Strategies
  

• Key Technologies of Mobile IPv6
  

• Improved mobile IPv6 protocol analysis