Permanent address and care-of address
Outline
Mobile network is simply no need to maintain throughout the access point has been connected, so the purpose is to use the mobile network to another can be maintained after the Internet can understand the terminal, continue to work, thus changing our traditional way of working, but there are some new problems arise, arise after you have solved.
problem
1. Different mobility needs
2. Network layer addresses the importance of maintaining unchanged
3. Support wired infrastructure
Therefore, to solve these problems have to do some work.
Addressing
Permanent address and care-of address
I believe that each of us have used the network, we went to him somewhere, where the network will give us assign a Ip address, the address is a permanent address, if communications were to end and the mobile communication, then, is established and the permanent address communication, but this node possible moves, then into another network, go to another site, will reassign an address, use the Ip address of the new allocation of communication, this network is called visited network, access this address, we called care-of address. 
Why care-of address?
Because after the correspondent has always been and permanent address for communication, and the mobile node is changed, the communication does not know, correspondent will still send data to the home network, the router in the routing table entry is the home network, so the home network, you need a home agent forwards the data to the delivery of new routers in the network, this router is called a foreign agent, to the mobile node according to the new address, when you want it sent directly to the correspondent.
Second, the routing of the mobile node
1. Simple routing
foreign agent by the home agent forwards the data to
the home agent: send to the foreign agent technology is tunneling through the
selection 2. Direct route
transmitted by the communication agency to obtain the address by the home agent, sent directly to the foreign agent, which is directly communications were sent to the new address.
