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Mobile IP

Myungchul Kim

mckim@icu.ac.kr

Tel: 042-866-6127

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– Mobile IP by Charles Perkins, Addison-Wesley, 1998.– communicating via laptop should be as natural as using a

telephone -> seamless roaming– 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– IP address (physical location)

• routing prefix (often determined by the netmask)• host number

– from the point of view of routing, the problem with mobility is that 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.

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– 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

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– IETF Mobile IP

– The mobility problem can be transformed into a routing problem (of network layer) in a natural way.

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– 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

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– 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 protocol1. 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.

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• IEEE Internet Computing, 58 – 69, Jan and Feb, 1998

• From dependence on fixed points of attachment to the flexibility afforded by mobility

• Mobile computing and networking

• The evolution of mobile networking will differ from that of telephony– Human vs computer applications

– Rate of adoption

– IP address: associated with a fixed network location

• Mobile IP (RFC 2002)– Use two IP addresses: a fixed home address and a care-of-address

that changes at each new point of attachment

– Make mobility transparent to applications and higher level protocols such as TCP (rather than IPv6)

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• TCP: the IP addresses and port numbers of both connection end-points

• To change the routing requires a new IP address associated with the new point of attachment -> Mobile IP– Home address: identify TCP connections

– Care-of-address

– Home network

– Home agent

– Foreign network

– Foreign agent

– Registration

– Redirection

– Reverse transformation

– Encapsulation

– Tunneling

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• 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 care-of address

– Registration lifetime

– Binding: home address, care-of address, and registration lifetime

– Binding update: remote redirect

– 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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– 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– Figure 2

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• 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.

• 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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• Renumbering of home network

• Automatic home agent discovery

• 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