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

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Chapter 1

After the Home Agent authenticates the Registration Request, it sends a Registration

Reply message to the Mobile Node. The Registration Reply also includes a lifetime for

the registration, which can be fixed or infinite.

Proxy ARP

After a Mobile Node registers a care-of address with its Home Agent, the Home Agent

sends a proxy ARP message to bind its link-level address to the Mobile Node’s home

address. The Home Agent will then capture packets addressed to the Mobile Node’s

home IP address. The Home Agent will also send proxy ARP replies (with its link-level

address) to any future ARP requests for the Mobile Node’s home address.

De-Registration

When a Mobile Node moves back to its home network it will determine that it is attached

to its home network based on the Agent Advertisements sent by its Home Agent. The

Mobile Node will de-register itself by sending a special Registration Request to its Home

Agent. The Home Agent will send a gratuitous ARP on behalf of the Mobile Node to link

the Mobile Node’s home address with the Mobile Node’s link-level address. The Mobile

Node will then operate without any Mobile IPv4 functionality.

Reverse Tunneling

Normally, the Mobile Node sends packets directly back to the Correspondent Node, as

shown in Figure 1-3. With reverse tunneling, the Mobile Node sends packets back to the

Correspondent Node through a tunnel between its Care-of Address and the Home Agent.

The Home Agent then forwards the packet to the Correspondent Node. Figure 1-4 and

Figure 1-5 show the return data path from the Mobile Node to the Correspondent Node

with reverse tunneling.

Figure 1-3 Return Data Path without Reverse Tunneling

Reverse tunneling is useful for installations with ingress filtering (filters that check

inbound packets for topologically correct source addresses). With reverse tunneling, the

packet leaving the foreign network will have a topologically correct source address,

because the source address in the outermost IP header will be an address from the

foreign network (the Care-of Address) instead of the Mobile Node’s home address. The

HP-UX Foreign Agent supports packets sent from the Mobile Node using the Direct

Delivery Style and the Encapsulating Delivery Style.