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 FAs advertisement expires, even though it hears this new
FA advertisement.

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