Mobile IP
Overview:
Standard
IP
Evolution of Mobile IP
How it works
Problems Assoc. with it
What is an IP?
A computer’s return address.
 Each computer on the network has a unique
set of numbers (0-255) in the form of
XXX.XXX.XXX.XXX
 Can be static or dynamic.
 IP addresses enable IP routing algorithms to
get packets to the correct network

Evolution of Mobile IP
In standard IP, end hosts are in fixed
physical locations. So, if a host moves to
another physical location, it has to change
its IP address
Mobile IP allows hosts to stay connected to
the internet regardless of their location.
Mobile IP

Mobile IP was created to allow users to
KEEP THE SAME IP ADDRESS while
‘traveling’ to a different network (which
may even be on a different wireless
operator),
This means that roaming individuals can
continue communication without breaking
their connection.
What makes it possible?
The three components of Mobile IP:
*Mobile Node (MN)
*Home Agent (HA)
*Foreign Agent (FA)
Home & Foreign Agents are also known as Mobile Agents
Mobile IP
Components & Relationship

How does it work? (1/3)
Each mobile node has two IP addresses:
•
•
A permanent home address that is assigned to the home network
and;
A temporary care-of address representing the current location of
the host.
Mobility is supported by transparently binding the
home address of the mobile node with its care-of
address.
How does it work (2/3)
Mobility binding is
maintained by
specialized routers
known as mobility
agents.
Mobility Binding Table
Table mapping a mobile node's home
address with its care-of address.
How does it work? (3/3)
Foreign Agents are
specialized routers on the
foreign network where the
mobile node is currently
visiting.
The FA maintains a visitor
list which contains
information about the
mobile nodes currently
visiting that network.
Visitor List
Mobile IP Protocol (1/5)
STAGE 1: Agent Discovery
Mobility agents periodically broadcasts Agent
Advertisement messages.
With this AA, a mobile node determines if it is on
the home or foreign network.
If a mobile node discovers that it is on the home
network operate without mobility services.
If it discovers it’s on a new network…….
Mobile IP Protocol (2/5)
STAGE 2: Registration
Mobile node registers with the foreign agent by sending a
Registration Request message.
Foreign agent registers on behalf of the mobile host by
sending a RR to the home agent.
Home agent receiving RR updates MBT.
Acknowledgement sent to Foreign Agent, which updates
its visitor list and relays reply to Mobile Node.
Mobile IP Protocol (3/5)
Mobile IP Protocol (4/5)
STAGE 3: In-Service
When a correspondent node communicates with the mobile
node, it sends an IP packet addressed to the permanent IP
address of the mobile node.
The home agent intercepts this packet and consults the MBT to
verify that the mobile node is currently visiting another
network.
HA obtains the MN care-of address and constructs a new IP
header containing MN’s care-of address as the destination IP
address.
The original IP packet is put into the payload of this IP packet
and is sent. Encapsulating an IP packet into the payload of
another is known tunneling.
Mobile IP Protocol (5/5)
When encapsulated packet reaches the mobile node's current
network, the FA decapsulates the packet and finds mobile
node's home address.
It then consults the visitor list to see if it has an entry for that
mobile node.
If an entry exists, the foreign agent retrieves the corresponding
media address and relays it to the mobile node.
When a mobile node wants to send a message to a
correspondent node, it forwards the packet to the FA, which in
turn relays the packet to the correspondent node using normal
IP routing.
Shortcomings of Mobile IP

Triangle Routing - when
the correspondent host and
the mobile host are in the
same network, the
messages will experience
unnecessary delay since
they have to be first routed
to the home agent that
resides in the home
network
Other Problems
Security – Firewalls often makes it hard for
Mobile IP because they block all classes of
incoming packets that do not meet specified
criteria.
 Competition from other protocols - other
alternative protocols also offer portability to
mobile computers. (E.g PPTP, L2TP)
 Slow Growth in wireless LAN?

Sources
Cisco Mobile IP solutions
http://www.cisco.com/
Association for Computing Machinery
http://www.acm.org
Mobile Networking Through Mobile IP
Charles E Perkins, Sun Microsystems