The problem with supporting mobile devices on the Internet is that the Internet is designed to

route packets hierarchically. The Mobile IPv$4$ protocol was created to address this challenge.

The most widely accepted standard for Mobile IPv$4,$ permits a mobile device to communicate

via the Internet in a relatively transparent manner. For example, a laptop computer from

UWA that uses IP address $130\mathrm{.}95\mathrm{.}1\mathrm{.}100$ when physically located at UWA, may still be

contacted, while it is in Sydney, with the IP address $130\mathrm{.}95\mathrm{.}1\mathrm{.}100.$

A mobile device$$s IP address must change as it moves from network to network. At the same

time, applications require a constant IP address. The apparent conflict is resolved by

maintaining two separate addresses for each device.

The first is the home address. This is the natural address for the device, the one that resides in

the address space of the home network. The home address is assigned by the home network

itself and stays with the device long$-$term. With regard to applications, this is always the IP

address of the device.

The second address is referred to as the care$-$of address. This address can potentially change

from minute to minute as a device travels through several foreign networks. To the routing

protocols of the Internet, this is the destination address of the device.

Any packets that are destined for the mobile device will be first routed to the home network,

since that is the network defined in the home address of the device.

Additional software, termed the home agent, will be present in a mobile IP$-$enabled network.

The home agent is responsible for intercepting any packets addressed to mobile devices that

are not currently $$at home,$$ and then forwarding those packets to the current care$-$of address

for the device. It does this by encapsulating the packet inside another packet destined for the

care$-$of address. This packet is then sent via the Internet, where standard routing protocols

ensure that it arrives at the foreign network temporarily hosting the device.

A foreign agent unwraps the packet and sends it to the mobile device via its home address,

which it has associated with a hardware destination address for the device. When the packet

arrives at the device, it is accepted as being appropriately addressed; it then travels up the

TCP$/$IP stack to the relevant application software.

i$)$ Draw one or more diagrams showing how a computer, that is neither in the home network nor

in the foreign network, can communicate with web server software running on the mobile

laptop.

On your diagram$($s$)$ draw a number of relevant IP packets, and clearly show all IP addresses

$($included any addresses in encapsulated packets$).$

ii$)$ With reference to your diagram$($s$),$ outline the potential security challenges associated with

Mobile IPv$4.$

iii$)$ Propose and discuss a mechanism to address these potential security challenges.