Mobile IP

Outline What is the problem at the routing layer when Internet hosts move?! Can the problem be solved? What is the standard solution? – mobile IP What are the problems with the solution? Other approaches?

Internet hosts & Mobility Wireless networking – allows Internet users to become mobile As users move, they have to be handed over from one coverage area to another (since the coverage areas of access points are finite) … Ongoing connections need to be maintained as the user moves …

Problems? What are the problems? The IP address associated with a mobile host is network dependent! When user connects to another network, IP address needs to change Packets belonging to ongoing connections somehow need to be delivered to the mobile host

Problems (Contd.)? What are the options? Make IP address host specific instead of network specific – obvious pitfalls? Change IP address of host and start using the new IP address in the subsequent packets belonging to the connections

Intuitive Solution Take up the analogy of you moving from one apartment to another What do you do? Leave a forwarding address with your old post-office! The old post-office forwards mails to your new post-office, which then forwards them to you

Mobile IP Basics Same as the post-office analogy Two other entities – home agent (old post-office), foreign agent (new post-office) Mobile host registers with home agent the new location Home agent captures packets meant for mobile host, and forwards it to the foreign agent, which then delivers it to the mobile host

Reverse path? Same as in the post-office analogy Packets originating from the mobile host go directly to the static corresponding host … Hence the name triangular routing MH HA SH FA MH

Mobile IP Entities Mobile host Corresponding host Home address Care-of address Home agent Foreign agent

Mobile IP in detail … Combination of 3 separable mechanisms: Discovering the care-of address Registering the care-of address Tunneling to the care-of address

Discovering the care-of address Discovery process built on top of an existing standard protocol: router advertisement (RFC 1256) Router advertisements extended to carry available care-of addresses called: agent advertisements Foreign agents (and home agents) send agent advertisements periodically A mobile host can choose not to wait for an advertisement, and issue a solicitation message

Agent advertisements Foreign agents send advertisements to advertise available care-of addresses Home agents send advertisements to make themselves known Mobile hosts can issue agent solicitations to actively seek information If mobile host has not heard from a foreign agent its current care-of address belongs to, it seeks for another care-of address

Registering the Care-of Address Once mobile host receives care-of address, it registers it with the home agent A registration request is first sent to the home agent (through the foreign agent) Home agent then approves the request and sends a registration reply back to the mobile host Security?

Registration Authentication Mobile IP requires the home agent and mobile host to share a security association MD5 with 128-bit keys to create digital signatures for registration requests to be used (registration message & header used for creating signature) Any problems? – replay attacks Solved by using an unique message identifier (timestamp or pseudorandom number)

Illustration

Foreign Agent Security? No foreign agent authentication required Foreign agent can potentially discard data once registration happens However, the problem is same as in unauthenticated route advertisements (RFC 1256) in the wireline context

Home agent discovery If the mobile host is unable to communicate with the home agent, a home agent discovery message is used The message is sent as a broadcast to the home agents in the home network

Tunneling to the Care-of address When home agent receives packets addressed to mobile host, it forwards packets to the care-of address How does it forward it? - encapsulation The default encapsulation mechanism that must be supported by all mobility agents using mobile IP is IP-within-IP (RFC 2003) Using IP-within-IP, home agent inserts a new IP header in front of the IP header of any datagram

Tunneling (contd.) Destination address set to the care-of address Source address set to the home agent’s address Tunnel header uses 4 for higher protocol id – this ensures that IP after stripping out the first header, processes the packet again Tunnel header of 55 used if IP minimal encapsulation used (RFC 2004)

Illustration

Recap Host mobility and Internet addresses Post-office analogy Home agent, foreign agent, care-of address, home address Registration and Tunneling IPv6 and Mobility support …

Recap Host mobility and Internet addresses Post-office analogy Home agent, foreign agent, care-of address, home address Registration and Tunneling IPv6 and Mobility support …

Mobile IP Basic Operation Entities Mobile host, home agent, foreign agent, corresponding host Discovering Care-of Addresses Agent advertisements Registering Care-of Address Security Tunneling to Care-of Address IP-within-IP encapsulation

Mobile IP Problems? Triangular routing overhead What is the worst case scenario? Registration latency and associated problems Ingress filtering and consequences Infrastructure required for mobile IP support? Firewalls

Mobile IP Optimizations Route optimization Smooth hand-offs

Route Optimizations Enable direct notification of the corresponding host Direct tunneling from the corresponding host to the mobile host Binding cache maintained at corresponding host Management of cache not stipulated (e.g. least used entry replacement)

Route optimizations (contd.) 4 types of messages Binding update Binding request Binding warning Binding acknowledge

Binding Update When a home agent receives a packet to be tunneled to a mobile host, it sends a binding update message to the corresponding host When a home agent receives a binding request message, it replies with a binding update message Also used in the the smooth-handoffs optimization

Binding Update (Contd.) Corresponding host caches binding and uses it for tunneling subsequent packets Lifetime of binding? Corresponding host that perceives a near-expiry can choose to ask for a binding confirmation using the binding request message Home agent can choose to ask for an acknowledgement to which a corresponding host has to reply with a binding ack message

Binding update (problem?) What happens when a mobile host moves?

Binding warning When a foreign agent receives a tunneled message, but sees no visitor entry for the mobile host, it generates a binding warning message to the appropriate home agent When a home agent receives a warning, it issues an update message to the corresponding host What if the foreign agent does not have the home agent address (why?) ?

Illustration Home Agent BU BW BR BA Foreign Agent Corresponding Host Mobile Host

Smooth Hand-offs When a mobile host moves from one foreign agent to another … Packets in flight to the old FA are lost and are expected to be recovered through higher layer protocols (e.g. TCP) How can these packets be saved?

Smooth Hand-offs Make previous FA forward packets to the new FA Send binding updates to the old FA through the new FA Such forwarding will be done for a pre-specified amount of time (registration lifetime) Update can also help old FA free any reserved resources immediately Why better?

Mobile IP in IPv6 Route optimization and smooth hand-offs used in IPv6 mobility Binding updates easier since IPv6 supports destination caches at sources IPv6 security inherently stronger than in IPv4. Hence, no explicit security mechanisms needed for mobile IP Source routing to be used instead of encapsulation (why?)

Recap Mobile IP problems Mobile IP Optimizations Mobility support in IPv6

Puzzle Power drill Power drill that drills square holes?! What would the cross-section of the power drill look like?