HP-UX Mobile IPv4 A.03.01 Administrator's Guide

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Chapter 1
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Co-located Care-of Address as the destination (b). The Mobile Node receives the packet
and removes the outer header to process the original header with the Correspondent
Node’s source address.
Figure 1-2 Data Path for Co-located Care-of Address
Agent Advertisements
Home Agents and Foreign Agents advertise their availability and Mobile IPv4 operating
parameters by periodically transmitting Agent Advertisement messages, usually using
the IP broadcast address (255.255.255.255). A Mobile Node discovers the Foreign Agent
Care-of Addresses available on a foreign network from Agent Advertisements sent by
Foreign Agents. Mobile Nodes also use Agent Advertisements to determine when they
have attached to a new foreign network, or have returned to their home network.
Agent Solicitation
When a Mobile Node attaches to a new network, it may send an Agent Solicitation
request to determine if there are mobility agents (Home Agents or Foreign Agents)
present. HP-UX Home Agents and Foreign Agents respond to Agent Solicitation requests
with Agent Advertisement messages.
Registration Requests and Static Key Authentication
When a Mobile Node attaches to a new foreign network, it sends a Registration Request
to its Home Agent to register its Care-of Address. If the Mobile Node is using a Foreign
Agent Care-of Address, the Registration Request is sent via the Foreign Agent. The
Registration Request includes an extension with a cryptographic authentication value
(HMAC-MD5 or keyed MD5). The Mobile Node calculates the authentication value based
on fields in the Registration Request and a static key (shared secret key) that is specified
on both the Home Agent and the Mobile Node.
The Home Agent authenticates the Mobile Node’s Registration Request by calculating
its own authentication value and comparing it with the authentication value from the
Mobile Node.