What is Mobile IPv6 ?
Mobile IPv6 is an IETF standard that has added the roaming capabilities of mobile nodes in IPv6 network. RFC 3775 has described this standard in detail. The major benefit of this standard is that the mobile nodes (as IPv6 nodes) change their point-of-attachment to the IPv6 Internet without changing their IP address.
This allows mobile devices to move from one network to another and still maintain existing connections. Although Mobile IPv6 is mainly targeted for mobile devices, it is equally applicable for wired environments. .
The need for Mobile IPv6 is necessary because the mobile nodes in fixed IPv6 network cant maintain the previously connected link (using the address assigned from the previously connected link) when changing location.
To accomplish the need for mobility, connections to mobile IPv6 nodes are made (without user interaction) with a specific address that is always assigned to the mobile node, and through which the mobile node is always reachable. Mobile IPv6 is expected to be used in IP over WLAN, WiMAX or BWA.
Definitions and IPv6 features that are needed by Mobile IPv6
Several terms and information are necessary to understand Mobile IPv6: A foreign link defines a link that is not the mobile nodes home link. A Care-of address denotes an address that is used by the mobile node while it is attached to a foreign link. Whenever a mobile node moves from the home link to a foreign link, it is always (still) reachable by its home address, regardless of its location in IPv6 network.
Home address signifies that the mobile node is logically connected to the home link. Also, the association of a home address with a care-of address for a mobile node is known as a binding. Home agent is a router (on the home link) that maintains registrations of mobile nodes that are away from home and their current addresses. A Correspondent node is an IPv6 (not necessarily Mobile IPv6 capable) node that communicates with a mobile node.
Mobile IPv6 uses the IPv6 features such as address auto-configuration, Neighbor discovery and extension header for its operation.
It uses both types of auto-configuration such as stateless (Network prefix + interface ID) and stateful auto-configuration (DHCPv6). The neighbor discovery feature allows performing the following:
- How each others presence is discovered and how to find routers
- How each others link layer addresses are determined
- How to maintain reachability information
Extension headers provide routing headers for route optimization and destinations option header for mobile node originated diagrams. In addition, Mobile IPv6 also requires mobile nodes to carry out IPv6 decapsulation.
Mobile IPv6 Operation
When a mobile node is away from home, it sends information about its current location to the home agent. A node that wants to communicate with a mobile node uses the home address of the mobile node to send packets. The home agent intercepts these packets, and using a table, tunnels the packets to the mobile node’s care-of address.
Mobile IPv6 uses care-of address as source address in foreign links. Also, to support natural route optimization, the Correspondent node uses IPv6 routing header than the IP encapsulation. The following discussion makes Mobile IPv6s understanding more clear by highlighting the benefit of Mobile IPv6 over mobile IPv4.
- Route Optimization is a built-in feature for Mobile IPv6. In mobile IPv4, this feature was available via an optional set of extensions that was not supported by all nodes.
- There is no requirement of foreign Agents in Mobile IPv6. As mentioned previously, Neighbour Discovery and Address Auto-configuration features enable mobile nodes to function in any location without the services of any special router in that location.
- There is no ingress filtering problem in Mobile IPv6 (In Mobile IPv4 this happens because the correspondent node puts its home address as the source address of the packet). In Mobile IPv6, the correspondent node puts the care-of address as the source address and having a Home Address Destination option, allow the use of the care-of address to be transparent over the IP layer.
Always On” Connectivity for Future Mobile Devices
Whereas IPv6 allows the deployment of millions of always-on, IP enabled devices, each with its own unique IP address, Mobile IPv6 enables mobile terminals to maintain their IP connectivity as they move across several networks. The goal for Mobile IPv6 is to provide provides seamless mobility for next generation mobile services and applications and across several access technologies such as WCDMA, WLAN etc. Additionally, Mobile IPv6 provides route optimization techniques to reduce handoff latencies.
Mobile IPv6 is a powerful enabler for the next generation of services such as peer-to-peer services, push services and Voice over IP (VoIP) which demand always-on global reachability and seamless mobility. Mobile IPv6, along with fast-handoffs and context transfer mechanisms will be essential for the large scale deployment of real-time services such as VoIP and broadcast services.