1. Mobility And IP Addressing

2. Mobility And IP Addressing
Network Prefix?
Consequence: when host moving to a new network
Host must change its IP address
Datagram forwarding must change
In the broadest sense, the term mobile computing refers to a system that allows computers to move from one location to another. Although wireless technologies allow rapid and easy mobility, wireless access is not required — a traveler might carry a lap top computer and connect to a remote wired network (e.g., in a hotel). The IP addressing scheme, which was designed and optimized for stationary hosts, makes mobility difficult. A prefix of each host address identifies the network to which the host attaches, and routers use the prefix to forward datagrams to the correct network for final delivery. As a result, moving a host to a new network requires one of two pos sible changes:

3. Mobility And IP Addressing
Mobility Via Host Address Change
dynamic address assignment
Mobility Via Changes In Datagram Forwarding
All routers install host-specific routes

4. The Mobile IP Technology
Officially named IP mobility support and popularly called mobile IP
Technology to support mobility

5. Mobile IP Pros Cons Allows host to retain original IP address
Does not require routers to install host-specific routes
Cons
datagram forwarding can be inefficient

6. Characteristics Of Mobile IP
Transparency
Transparent to applications and transport and routers
Backward Compatibility
Interoperates with standard IPv4 and IPv6 respectively
Scalability
solution permits mobility across the global Internet

7. Characteristics Of Mobile IP
Security
Mobile IP can ensure that all messages are authenticated
Macro Mobility
Intended for working away from home rather than moving at high speed

8. General Approach – Mobile IP Working
Host visiting a foreign network obtains second IP address that is local to the site
Host informs router on home network

9. General Approach – Mobile IP Working
Router at home uses second address to forward datagrams for the host to the foreign network
Datagrams sent in a tunnel
Uses IP-in-IP encapsulation

10. Mobile IP Working
To support mobility, a host’s home network must include a special network system - home agent
mobile host registers a secondary address with its home agent

11. Mobile IP Working
Home agent intercept each datagram that arrives for the host’s permanent address and forward the datagram to the host’s current location.
When a mobile host returns home, it must contact the home agent to deregister

12. Mobile IPv4 Addressing
a mobile host’s primary or home address is a conventional IPv4 address
Applications on a mobile host always use the primary address; they remain unaware of any other address

13. Mobile IPv4 Addressing
The host’s secondary address (care-of address), is a temporary address that is used only by the mobile IP software on the host.
A care-of address is only valid for a given foreign network.

14. Mobile IPv4
supports two types of care- of addresses that differ in the method by which the address is obtained and in the way datagram forwarding occurs
Co-located
Foreign Agent

15. Co-located
Foreign network does not run a foreign agent
Host uses DHCP to obtain temporary address
Host registers directly with home agent

16. Foreign Agent Foreign network runs system known as foreign agent
Visiting host registers with foreign agent
Foreign agent assigns host a temporary address
Foreign agent registers host with home agent

17. IPv4 Foreign Agent Discovery
IPv4 foreign agent discovery uses the ICMP router discovery mechanism
router sends an ICMP router advertisement message
host to send an ICMP router solicitation

18. A router that acts as a foreign agent appends a mobility agent extension to each message
the extension specifies the network prefix, which a mobile host uses to determine that it has moved to a new network.

19. ICMP router discovery message - Extension format

20. ICMP router discovery message - Extension format
LENGTH - Size of the extension message in octets, excluding the TYPE and LENGTH.
LIFETIME - Maximum amount of time in seconds that the agent is willing to accept registration requests, with all 1s indicating infinity.

21. ICMP router discovery message - Extension format
SEQUENCE NUM - Sequence number for the message to allow a recipient to determine when a message is lost
CARE OF ADDRESS - address of at least one foreign agent.
CODE - Each bit defines a specific feature of the agent as listed

22. CODE field
Bits of the CODE field of an IPv4 mobility agent advertisement

23. IPv4 Registration
The registration protocol allows a host to
Register with an agent on the foreign network, if needed
Register with its home agent to request forwarding
Renew a registration that is due to expire
Deregister after returning home

24. IPv4 Registration mobile host performs registration directly
co-located care-of address
mobile host performs registration directly
foreign agent care-of address
mobile host allows the foreign agent to register with the home agent on the host’s behalf

25. IPv4 Registration Message Format
All registration messages are sent via UDP; agents use port 434.
A registration message begins with a set of fixed-size fields followed by variable-length extensions.
Each request is required to contain a mobile-home authentication extension that allows the home agent to verify the mobile’s identity.

26. LIFETIME - specifies the number of seconds the registration is valid.
Format of an IPv4 mobile IP registration request or mobile IP reply message
IDENTIFICATION - Contains a 64-bit number generated by the mobile that is used to match requests with incoming replies and to prevent the mobile from accepting old messages.
TYPE - specifies whether the message is a request (1) or a reply (3)
LIFETIME - specifies the number of seconds the registration is valid.
a zero requests immediate deregistration, and all 1s specifies an infinite lifetime.
FLAGS/CODE field are used as a result code in a registration reply message

27. Datagram Transmission, Reception, And Tunneling

28. The Two-Crossing Problem
mobile IP handles spatial locality poorly

29. Communication With An IPv4 Foreign Agent
If a mobile does not have a unique foreign address, a foreign agent must use the mobile’s home address for communication.
Instead of relying on ARP for address binding, the agent records the mobile’s hardware address when a request arrives and uses the recorded information to supply the necessary binding.