Agents Access Large Networks
By setting up a reverse tunnel from the cellular node’s care-of tackle to the house agent, you ensure a topologically right source address for the IP knowledge packet. A cellular node can request a reverse tunnel between its foreign agent and its house agent when the cell node registers. A reverse tunnel is a tunnel that starts at the cellular node’s care-of tackle and terminates at the home agent. The following illustration shows the Mobile IP topology that uses a reverse tunnel. When appearing as transmitter, a cell node sends packets directly to the opposite communicating node, with out sending the packets through the home agent, utilizing its permanent home address as the source tackle for the IP packets.
A mobile node registers with its residence agent utilizing a registration request message in order that its residence agentcan create or modify a mobility binding for that cell node (for example, with a brand new lifetime). The international agent can relay the registration request to the home agent. However, if the cellular node is registering a co-positioned care-of address, then the cellular node can ship the registration request directly to the home agent.
If the registration reply is legitimate, the Foreign Agent provides the Mobile Node to its visitor list, establishes a tunnel to the Home Agent, and creates a routing entry for forwarding packets to the home tackle. During the agent discovery phase, the Home Agent and Foreign Agent advertise their providers on the community by utilizing the ICMP Router Discovery Protocol (IRDP). The Mobile Node listens to these commercials to find out if it is connected to its home community or international network. A reciprocal tunnel is about up by the Home Agent to the care-of tackle (present location of the Mobile Node on the overseas network) to route packets to the Mobile Node as it roams. Home agents and international brokers support tunneling datagrams using one of many available encapsulation methods (IP in IP Encapsulation, Minimal Encapsulation, or Generic Routing Encapsulation).
Each cellular node, international agent, and residential agent helps a mobility safety affiliation between the assorted Mobile IP components, indexed by their security parameter index (SPI) and IP handle. In the case of the mobile node, this address is its home tackle. Registration messages between a cellular node and its home agent are authenticated with the Mobile-house authentication extension. In addition to Mobile-house authentication, which is necessary, you can use the optional Mobile-overseas agent and Home-overseas agent authentications. Registration messages trade data between a mobile node, a foreign agent, and the house agent.
This is known as triangular routing or “route optimization” (RO) mode. If wanted, the overseas agent might employ reverse tunneling by tunneling the cellular node’s packets to the house agent, which in flip forwards them to the communicating node. This is required in networks whose gateway routers examine that the supply IP tackle of the cellular host belongs to their subnet or discard the packet otherwise. In Mobile IPv6 (MIPv6), “reverse tunneling” is the default behaviour, with RO being an optionally available behaviour. The route optimization provides a conceptual information construction, the binding cache, to the correspondent node.
Now, a tunnel will be established between the home agent and the overseas agent by the process of tunneling. However, this information path is topologically incorrect as a result of it does not reflect the true IP network source for the info…”somewhat, it displays the house network of the Mobile Node. Because the packets show the home community as their source inside a foreign network, an entry control listing on routers in the community referred to as ingress filtering drops the packets instead of forwarding them. A feature called reverse tunneling solves this downside by having the Foreign Agent tunnel packets back to the Home Agent when it receives them from the Mobile Node. The Foreign Agent checks the validity of the registration reply, together with ensuring that an related registration request exists in its pending record.
The following illustration exhibits a community topology with two privately addressed mobile nodes that use the same care-of address when registered to the identical overseas agent. The previous description of Mobile IP assumes that the routing inside the Internet is independent of the data packet’s supply handle. However, intermediate routers may verify for a topologically right source address. If an intermediate router does check, you must set up a reverse tunnel.
The binding cache incorporates bindings for cell node…™s residence address and its present care-of-handle. After this the correspondent node can directly tunnel packets to the cell node. Data packets contains correspondent node…™s address (Source) and home address (Destination). But now cellular node just isn’t within the home community, it has moved into the foreign network. Foreign agent sends the care-of-address to the house agent to which all of the packets should be sent.
When a mobile node has a personal tackle, the mobile node can only communicate with a correspondent node through a reverse tunnel. The privately addressed correspondent node should belong to the same residence agent’s administrative area.
Mobile nodes that use a co-located care-of addresscan obtain tunneled datagrams using any encapsulation type. The residence agent also forwards packets to the mobile node when the cell node is away from its home network.