Mobility And IP Addressing

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:

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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.

ICMP router discovery message - Extension format

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.

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

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

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

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

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.

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

Datagram Transmission, Reception, And Tunneling

The Two-Crossing Problem mobile IP handles spatial locality poorly

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.