Mobile IP Technology and Applications

Mobile IP Registration 49

Mobile IP Example

We now look at a Mobile IP example to get a good feel for the protocol. Consider a Mobile

Node with a single interface whose Home Address is 192.168.10.30 and Home Agent is

192.168.10.1. In this example, the Mobile Node roams away from home to FA 192.168.100.6,

and then to another FA, 192.168.200.6. It then finds itself still roaming, but not within the

domain of a FA. At this point, it obtains a Colocated CoA and continues to roam. After some

time, it returns home. The example is as follows:

1 The Mobile Node powers on and hears a Mobility Agent advertisement with the H bit set

and router address as 192.168.10.1. Using this information and other relevant information

from the advertisement, the Mobile Node recognizes that it is at home and does nothing.

2 At some later time, the Mobile Node hears another Mobility Agent advertisement with the

F bit set, router address as 192.168.100.6 with a prefix length extension of /24, and CoA

as 192.168.100.6. The Mobile Node detects that it has moved into a foreign domain and

can request services by this FA. Using the new network algorithm, the Mobile Node

determines that it needs to initiate a Mobile IP handover.

3 The Mobile Node sends a RRQ to its Home Agent through the FA. It conveys its new CoA

(192.168.100.6) and its Home Address (192.168.10.30). As required, the Mobile Node

appends an MHAE with the correct security credentials. The IP source of the RRQ is the

Mobile Node’s Home Address (192.168.10.30), and the IP destination is the FA

(192.168.100.6).

4 The FA receives the RRQ, validates the requested services, creates an entry in its pending

registration table, and forwards it on to the Home Agent. The IP source of the RRQ is now

the FA 192.168.100.6, and the IP destination is the Home Agent 192.168.10.1.

5 The Home Agent authenticates and then validates the RRQ. The Home Agent establishes

the mobility binding and Mobile IP tunnel to the CoA, sends a gratuitous ARP on the

Home Network, and sends a positive RRP to the Mobile Node through the FA (the IP

source is the Home Agent 192.168.10.1, and the IP destination is the FA 192.168.100.6).

As required, the Home Agent appends an MHAE with the correct security credentials.

6 The FA receives the RRP, verifies that it is a successful reply, and changes the pending

registration entry into a visitor entry for the Mobile Node. The FA then forwards the RRP

to the Mobile Node using link-layer addressing.

7 The Mobile Node receives the RRP and enjoys the established Mobile IP services for the

lifetime granted, or until it moves again and must reregister.

8 At some time later, the Mobile Node hears a Mobility Agent advertisement with the F bit

set, router address 192.168.200.6 with a prefix length extension of /24, and CoA of

192.168.200.6. This time, the Mobile Node uses the steady-state algorithm and, thus, does

not do anything until its current FA’s advertisement expires, even though it hears this new

FA advertisement.