A second Mobile IPv6 node type is the home agent , which acts as a support node on the home network for Mobile IPv6 mobile nodes. A home agent is a router which has a proxy function for mobile nodes while they are away from home. The destination addresses of packets sent to mobile nodes are set to the home addresses of the mobile nodes. A home agent intercepts all packets which are addressed to the mobile node’s home address, and thus delivered to the home network on behalf of the mobile nodes.
This forwarding mechanism is the core feature provided by the Mobile IPv6 protocol. All IPv6 nodes which want to communicate with a mobile node can use the home address of the mobile node as a destination address, regardless of the current location of the mobile node. Those packets sent from an IPv6 node to the home address of a mobile node are delivered to the home network by the Internet routing mechanism where the home agent of the mobile node receives the packets and forwards the packets appropriately. For the reverse direction, a mobile node uses its home address as a source address when sending packets. However, a mobile cannot directly send packet nodes whose source address is a home address from its current location if it is away from home, since source addresses are not topologically correct. Sending a packet whose source address is out of the range of the network address of the sender node is a common technique when an attacker tries to hide its location when he is attacking a specific node. Such a packet may be considered as an attack. Because of this reason, the first hop router may drop such topologically incorrect packets to avoid the risk of the source spoofing attack. To solve this problem, a mobile node uses the IPv6 in IPv6 encapsulation technology. All packets sent from a mobile node while away from home are
sent to its home agent using the encapsulation mechanism. The home agent decapsulates the packets and forwards them as if the packets were sent from the home network.
A third type of Mobile IPv6 node is called the correspondent node . A correspondent node is an IPv6 node that communicates with a mobile node. A correspondent node does not have to be Mobile IPv6-capable, other than supporting the IPv6 protocol; any IPv6 node can be a correspondent node. Since the Mobile IPv6 specifi cation provides a backward compatibility to all IPv6 nodes which do not support Mobile IPv6, all IPv6 nodes can communicate with mobile nodes without any modification. However, as we have described in the previous paragraph, all packets between a mobile node and a correspondent node must be forwarded basically by the home agent of the mobile node. This process is sometimes redundant, especially when a correspondent node and a mobile node are located on topologically near networks. To solve this redundancy, Mobile IPv6 provides an optimization mechanism called the route optimization mechanism which a correspondent node may support. A mobile node can send packets directly to a correspondent node using the care-of address of the mobile node as a source address. The information of the home address of a mobile node is carried by the newly defined option for the Destination Options Header. Also, a correspondent node can send packets directly to the care-of address of a mobile node. In this case, the information of the home address is carried by the Routing Header.
A correspondent node may itself be a mobile node. In this case, two moving nodes can communicate with each other without terminating their sessions regardless of their points of attachment to the Internet.
Source of Information : Elsevier Wireless Networking Complete 2010