Mobile IP: enable mobility for IP-based networks CS457 presentation Xiangchuan Chen Nov 6, 2001

Main contents Mobility vs Portability The challenges The basic Mobile IP protocol Mobility support in IPv6

Mobility vs Portability SupportWeb browsing Long lasting telnet Persistent host identity MobilityYes PortabilityYesNo

The current goal 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 ? 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 ? NO!! A connection is identified by two communication endpoints, each being identified by a pair. From the view point of transport layer, changeable addresses alone cause connection loss during the change of attachment points.

Mobile IP introduces Home address: on home network  unchanged, usually its IP address  for endpoint identification. Care-of address: on foreign network  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) 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) Accordingly, different actions are taken:  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) 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) 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 Increased impact of possible network partitions Increased load of the network Increased delay in delivering packets

Mobility support in IPv6 (I) New features in IPv6Effects Larger address space, Automatic address configuration Access points instead of foreign agents Programmable routers The new care-of address is sent to the home agent, the router in previous network, and the correspondent nodes

Mobility support in IPv6 (II) New features in IPv6Effects Redefined source routing process Avoiding IP spoofing Improved securityAvoiding malicious remote redirection IPv6 headerIP6-in-IP6 encapsulation

Avoid triangle routing (I) Every host caches the care-of addresses of one or more mobile hosts When sending an IP datagram to a mobile host:  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) 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, 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