Mobile IP: enable
mobility for IP-based networks
CS457 presentation
Xiangchuan Chen
Nov 6, 2001
Main contents
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Mobility vs Portability
The challenges
The basic Mobile IP protocol
Mobility support in IPv6
Mobility vs Portability
Support
Web
browsing
Yes
Long
lasting
telnet
Yes
Persistent
host
identity
Yes
Mobility
Portability
Yes
No
No
The current goal
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Let laptops operate TCP/IP as easily as
a desktop computer because they are
as capable as desktops.
Or, The datagrams to mobile hosts are
forwarded correctly.
Where is the problem ?
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Each router forwards each datagram by
matching the destination IP address of
it with the entries of subnet prefix.
From the view point of routing, mobile
hosts move from one IP subnet to
another, but have the WRONG subnet
prefix for the destination subnet.
Will a changeable address do ?
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NO!!
A connection is identified by two
communication endpoints, each being
identified by a <IP, port> pair.
From the view point of transport layer,
changeable addresses alone cause
connection loss during the change of
attachment points.
Mobile IP introduces
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Home address: on home network
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Care-of address: on foreign network
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unchanged, usually its IP address
for endpoint identification.
Identify current location
a globally routable address
assigned by the current foreign network
Home agent and Foreign agent
The abstract model
The protocol outline (I)
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Agents advertise their presence via
agent advertisement messages. Mobile
hosts may solicit.
Upon receiving an advertisement, a
mobile host determines whether it is on
its home network or a foreign network.
The protocol outline (II)
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Accordingly, different actions are taken:
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The home network  operate without
mobility services
Just moved into a foreign network 
obtain a care-of address
just returned to the home network 
deregister with its home agent
The protocol outline (III)
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After getting a new care-of address, a
mobile host registers it with its home
agent by using registration
request/reply messages.
Then the home agent intercepts all
datagrams sent to the mobile host’s
home address, and tunnels them to the
care-of address.
The protocol outline (IV)
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The foreign agent decapsulates all
datagrams, and delivers them to the
corresponding mobile nodes.
Datagrams from the mobile node can
be delivered to their destination w/ or
w/o passing through the home agent.
Triangle routing
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Increased impact of
possible network
partitions
Increased load of
the network
Increased delay in
delivering packets
Mobility support in IPv6 (I)
New features in IPv6 Effects
Larger address space, Access points instead of
foreign agents
Automatic address
configuration
Programmable
The new care-of address
routers
is sent to the home agent,
the router in previous
network, and the
correspondent nodes
Mobility support in IPv6 (II)
New features in IPv6
Effects
Redefined source
routing process
Avoiding IP spoofing
Improved security
Avoiding malicious
remote redirection
IPv6 header
IP6-in-IP6
encapsulation
Avoid triangle routing (I)
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Every host caches the care-of addresses
of one or more mobile hosts
When sending an IP datagram to a
mobile host:
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If a cache entry is available for the host 
tunnel the datagram directly to the care-of
address
Otherwise, process it normally
Avoid triangle routing (II)
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When the home agent intercepts a
datagram for a mobile host, it should
send a binding update message to the
original source
If receive a binding message, the host
updates its binding cache after
authenticating with the home agent
By Mobile IP,
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Mobility is enabled, even across
heterogeneous media
A mobile host is able to communicate
with other hosts that do not implement
Mobile IP
There is no additional constraints on the
assignment of IP addresses
No requirement is placed on the layer-2