• References
– Mobile Computing by T. Imielinski and H. F. Korth, Kluwer, 1996.
– Andrew T. Campbell, Javier Gomez, and et al., Design, Implementation,
and Evaluation of Cellular IP, IEEE Personal Comm., pp. 42 - 49, Aug.
2000.
– Henning Schulzrinne and Jonathan Rosenberg, The Session Initiation
Protocols, IEEE Comm., pp. 134-141, Oct. 2000.
– Hong Liu and Petros Mouchtaris, Voice over IP Signaling, pp. 142-148,
Oct. 2000.
– IPng and the TCP/IP Protocols by Stephen A. Thomas, Wiley, 1996.
– Yoram Bernet, The Complementary Roles of RSVP and Differentiated
Services in the Full-Service QoS Network, IEEE Comm., pp. 154 - 162,
Feb., 2000.
1
Mobile IP
Myungchul Kim
mckim@icu.ac.kr
2
– Ch. 1 and 2 of Mobile IP Design Principles and Practices by
Charles E. Perkins, Addison-Wesley, 1998.
– communicating via laptop should be as natural as using
a telephone -> seamless roaming
– IP address (physical location)
• routing prefix (often determined by the netmask)
• host number
– two conflicting requirements for
• a changeable network address (for routability) and
• a stable network address (for identification purposes for
transport protocols, notably TCP)
• associations between the two network addresses involved ->
nomadic (or mobile) computing
3
– the problem with mobility: mobile computers move
from one IP subnet to another, but have the wrong
subnet prefix for the destination subnet.
– Mobile IP: one IP address is available for locating the
mobile computer and another is available for identifying
a communication endpoint on the mobile computer.
4
– care-of address, home network, home address,
readdressing (home address -> care-of address),
inverse readdressing
– the abstract functions to support mobility
• readdressing at the home network
• associating the home address and the care-of address of the
mobile node
• delivering the datagram to the care-of address
• inverting the readdressing operation once the datagram arrives
at the care-of address
5
– IETF Mobile IP
– where mobile networking fits? The mobility problem
can be transformed into a routing problem (of network
layer) in a natural way.
6
– Mobile IP
• a modification to IP that allows nodes to continue to
receive datagrams no matter where they happen to
be attached to the Internet.
• Scalability
– Functions of Mobile IP
• agent discovery (solicitation by mobile node)
• registration (directly with its home agent or through
a foreign agent)
• tunneling
– protocol tunneling to hide a mobile node’s home
address from intervening routers between its home
network and its current location
7
– two ways to acquire a care-of address
• the care-of address is an IP address of the foreign agent: it
allows many mobile nodes to share the same care-of address.
• A colocated care-of address is a care-of address acquired by
the mobile node as a local IP address (through DHCP)
– rough outline of the operation of the Mobile IP protocol
1. Mobility agents advertise their presence via agent
advertisement messages. A mobility node may optionally
solicit an agent advertisement message by using an agent
solicitation message.
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2. A mobile node receives an agent advertisement and determines
whether it is on its home network or a foreign network.
3. When the mobile node detects that it is located on its home
network, it operates without mobility services. If returning to
its home network from being registered elsewhere, the mobile
node deregisters with its home agent through a variation of the
normal registration process.
4. When a mobile node detects that it has moved to a foreign
network, it obtains a care-of address on the foreign network.
5. The mobile node, operating away from home, then registers its
new care-of address with its home agent through the exchange
of a registration request and registration reply message.
6. Datagrams sent to the mobile node’s home address are
intercepted by its home agent to the mobile node’s care-of
address, received at the tunnel endpoint and finally delivered to
the mobile node.
7. In the reverse direction, datagrams sent by the mobile node
may be delivered to their destination using standard IP routing
mechanisms, without necessarily passing through the home
agent.
9
– Charles E. Perkins, Mobile Networking through Mobile IP, IEEE Internet
Computing, pp. 58 - 69, Jan. and Feb. 1998.
• Mobile IP
– Discovering the care-of address
– Registering the care-of address
– Tunneling to the care-of address
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• Discovering the Care-of Address
– Router advertisement (RFC 1256) -> agent
advertisement
• Allows for the detection of mobility agents
• Lists one or more available care-of addresses
• Informs the mobile nodes about special features
provided by foreign agents, e.g., alternative
encapsulation techniques
• Lets mobile nodes determine the network number
and status of their links to the Internet, and
• Lets the mobile nodes know whether the agent is a
home agent, a foreign agent, or both
– Router solicitations (RFC 1256) -> agent solicitation
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• Registering the Care-of address
– When a home agent accepts the registrations request, it begins
to associate the home address of the mobile node with the careof address(next slide)
– Registration lifetime
– Binding: home address, care-of address, and registration
lifetime
– Each mobile node and home agent must share a security
association and be able to use Message Digest 5 (RFC 1321)
with 128-bit keys to create unforgeable digital signatures for
registration requests.
– Replay attack
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13
– Two may ways to make the identification field unique
• Timestamp
• Pseudorandom number
– The identification field for pending registration request
– Automatic home agent discovery: broadcast IP address
-> rejection to the mobile node (HA IP address)
• Tunneling to the Care-of Address
– 4: IP-within-IP
– 55: minimal encapsulation
– next slide
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15
• Changes with IP version 6
– Mobility support in IPv6
• A mobile node can configure its a care-if address by using
Stateless Address Autoconfiguration and Neighbor Discovery
in IPv6.
• Foreign agents are not required.
• IPv6-within-IPv6 tunneling is also specified.
– Route optimization
• Packets delivery without assistance from the home agent
– Security
• Strong authentication and encryption feature
– Cost of performance
– Internet-wide key management
– Source routing
• Security
• Performance
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– In IPv6, key management between the mobile node and
correspondent nodes is more likely to be available
– Other features supported by IPv6 mobility
• Coexistence with Internet ingress filtering: many border
routers discard packets coming from within the enterprise if
the packets do not contain a source IP address configured for
one of the enterprise’s internal networks.
• Smooth handoff
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• Ongoing work and open questions
– Routing inefficiencies
• Triangle routing
• Route optimization
– Security issues
• Firewalls
• Such communications, originating from the mobile node, carry
the mobile node’s home address, and would thus be blocked by
the firewall.
– Ingress filtering
– User perceptions of reliability
– Slow growth in the wireless LAN market
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– Competition from other protocols
• PPTP and L2TP based on PPP
– Current development efforts
• Vertical handoffs between dissimilar media
• Ad-hoc networking
19