Mobile IP

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Mobile IP (or MobileIP) is an Internet Engineering Task Force (IETF) standard communications protocol that is designed to allow mobile device users to move from one network to another while maintaining a permanent IP address. Mobile IPv4 is described in IETF RFC 3344 (Obsoleting both RFC 3220 and RFC 2002), and updates are added in IETF RFC 4721. Mobile IPv6 is described in IETF RFC 3775.

Contents 1 Introduction 1.1 Applications 2 How Mobile IP works 2.1 Future 3 See also 4 External links

[edit] Introduction

The Mobile IP protocol allows transparent routing of IP datagrams on the Internet. Each mobile node is identified by its home address disregarding its current location in the Internet. While away from home, a mobile node is associated with a care-of address which gives information about its current location. Mobile IP specifies how a mobile node registers with its home agent and how the home agent routes datagrams to the mobile node through a tunnel. Mobile IP provides an efficient, scalable mechanism for roaming within the Internet. Using Mobile IP, nodes may change their point-of-attachment to the Internet without changing their IP address. This allows them to maintain transport and higher-layer connections while moving. Node mobility is realized without the need to propagate host-specific routes throughout the Internet routing fabric.

[edit] Applications

Mobile IP is most often found in wired and wireless environments where users need to carry their mobile devices across multiple LAN subnets with different IP addresses. It may for example be used in roaming between overlapping wireless systems, for example IP over DVB, WLAN, WiMAX and BWA. Currently, Mobile IP is not required within cellular systems such as 3G, to provide transparency when internet users migrate between cellular towers, since these systems provide their own data link layer handover and roaming mechanisms. However, it is often used in 3G systems to allow seamless IP mobility between different Packet Data Serving Node (PDSN) domains. For Release 8, MIP and different variations like PMIP will be supported by the EPS (Evolved Packet System), at least for non-3GPP accesses.

In many applications (VPN and VoIP, to name a few), sudden changes in network and IP-address can cause problems.

[edit] How Mobile IP works

In brief, Mobile IP works as follows. A mobile node can have two addresses - a permanent home address and a care of address, which is associated with the network the mobile node is visiting. There are two kinds of entities in Mobile IP:

• A home agent stores information about mobile nodes whose permanent address is in the home agent's network.
• A foreign agent stores information about mobile nodes visiting its network. Foreign agents also advertise care-of addresses, which are used by Mobile IP.

A node wanting to communicate with the mobile node uses the home address of the mobile node to send packets. These packets are intercepted by the home agent, which uses a table and tunnels the packets to the mobile node's care-of address with a new IP header, preserving the original IP header. The packets are decapsulated at the end of the tunnel to remove the added IP header and delivered to the mobile node.

When acting as sender, mobile node simply sends packets directly to the other communicating node through the foreign agent. This is known as triangular routing. If needed, the foreign agent could employ reverse tunneling by tunneling mobile node's packets to the home agent, which in turn forwards them to the communicating node. This will be needed in networks whose gateway routers have ingress filtering enabled and hence the source IP of the mobile host would need to belong to the subnet of the foreign network else the packets will be discarded by the router.

The Mobile IP protocol defines the following:

• an authenticated registration procedure by which a mobile node informs its home agent(s) of its care-of-address"(es);

• an extension to ICMP Router Discovery, which allows mobile nodes to discover prospective home agents and foreign agents; and

• the rules for routing packets to and from mobile nodes, including the specification of one mandatory tunneling mechanism and several optional tunneling mechanisms.

[edit] Future

Enhancements to the Mobile IP technique, such as Mobile IPv6 and Hierarchical Mobile IPv6 (HMIPv6), are being developed to improve mobile communications in certain circumstances by making the processes more secure and more efficient.

Researchers are also working to create support for mobile networking without requiring any pre-deployed infrastructure as required by MIP. One such example is Interactive Protocol for Mobile Networking (IPMN) which promises supporting mobility on a regular IP network just from the network edges by intelligent signaling between IP at end-points and application layer module with improved quality of service.

[edit] See also

• Handoff
• Roaming
• Mobility management
• Mobile IPv6
• Vertical handoff

[edit] External links

• Inside Mobile IP[1]
• Protocols for Adaptive Mobile and Wireless Networking [2]
• RFC 3344 - IP Mobility Support for IPv4
• RFC 4721 - Mobile IPv4 Challenge/Response Extensions
• Mobile IP (a nice tutorial by Debalina Ghosh) [3]
• Mobile IP explained (another tutorial) [4]
• Mobile IPv6 - A short Introduction [5] (PDF)
• RFC 3024 - Reverse Tunneling for Mobile IP
• Introduction to Mobile IP[6]