Q22Mobile Computing
Question
Write detailed notes on Mobile IP. Explain agent discovery, registration, and tunneling in detail.
Answer
Mobile IP enables mobility across networks. It involves Agent Discovery (finding FA/HA), Registration (updating location), and Tunneling (forwarding packets).
<h3>Overview of Mobile IP</h3><p>Mobile IP is designed to provide seamless internet connectivity for mobile nodes moving between different subnets. It ensures that the mobile node's IP address remains constant, allowing active TCP connections to survive physical movement.</p>
<h3>Agent Discovery</h3><p>Agent Discovery allows a Mobile Node (MN) to determine its current location (whether it is on its home network or a foreign network) and obtain a Care-of Address (COA).</p><ul><li><strong>Agent Advertisements:</strong> Home Agents (HA) and Foreign Agents (FA) periodically broadcast Agent Advertisement messages (extensions of ICMP Router Discovery) on their local subnets.</li><li><strong>Agent Solicitations:</strong> If an MN does not hear advertisements, it can actively broadcast an Agent Solicitation message to prompt agents to respond.</li><li><strong>Process:</strong> By analyzing the advertisements, the MN determines if it has moved. If it is on a foreign network, it acquires a COA from the FA's advertisement (FA-COA) or via DHCP (Co-located COA).</li></ul>
<h3>Registration</h3><p>Once the MN gets a COA, it must register it with its Home Agent.</p><ul><li>The MN sends a Registration Request message to the FA, which forwards it to the HA.</li><li>The HA verifies the MN's credentials, updates its binding cache (associating the MN's home address with the new COA), and sends a Registration Reply back to the FA.</li><li>The FA updates its visitor list and forwards the reply to the MN.</li></ul>
<h3>Tunneling and Encapsulation</h3><p>When a Correspondent Node (CN) sends packets to the MN's home address, the HA intercepts them using proxy ARP.</p><ul><li><strong>Encapsulation:</strong> The HA wraps the original IP packet inside a new IP packet. The new header has the HA as the source and the COA as the destination. This is called IP-in-IP encapsulation.</li><li><strong>Tunneling:</strong> The packet travels through the internet 'tunnel' to the FA.</li><li><strong>Decapsulation:</strong> The FA receives the encapsulated packet, strips off the outer IP header, and delivers the original IP packet to the MN over the local wireless link.</li></ul>
