IPv6
IPv6
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Stateless Auto Configuration
by Kaushik Das

Introduction


Stateless Auto Configuration is an important feature offered by the IPv6 protocol. It allows the various devices attached to an IPv6 network to connect to the Internet using the Stateless Auto Configuration without requiring any intermediate IP support in the form of a Dynamic Host Configuration Protocol (DHCP) server. A DHCP server holds a pool of IP addresses that are dynamically assigned for a specified amount of time to the requesting node in a Local Area Network (LAN).
  IPv6

Stateless Auto Configuration is a boon for the Network Administrators since it has automated the IP address configuration of individual network devices. Earlier, configuration of the IP addresses was a manual process requiring support of a DHCP server. However, IPv6 allows the network devices to automatically acquire IP addresses and also has provision for renumbering/reallocation of the IP addresses en masse. With a rapid increase in the number of network devices connected to the Internet, this feature was long overdue. It simplifies the process of IP address allocation by doing away with the need of DHCP servers and also allows a more streamlined assignment of network addresses thereby facilitating unique identification of network devices over the Internet.

The auto configuration and renumbering features of Internet Protocol version 6 are defined in RFC 2462. The word "stateless" is derived from the fact that this method doesn't require the host to be aware of its present state so as to be assigned an IP address by the DHCP server. The stateless auto configuration process comprises of the following steps undertaken by a network device:

  Link-Local Address Generation - The device is assigned a link-local address. It comprises of '1111111010' as the first ten bits followed by 54 zeroes and a 64 bit interface identifier.

  Link-Local Address Uniqueness Test - In this step, the networked device ensures that the link-local address generated by it is not already used by any other device i.e. the address is tested for its uniqueness.

  Link-Local Address Assignment - Once the uniqueness test is cleared, the IP interface is assigned the link local address. The address becomes usable on the local network but not over the Internet.

  Router Contact - The networked device makes contact with a local router to determine its next course of action in the auto configuration process.

  Router Direction - The node receives specific directions from the router on its next course of action in the auto configuration process.

  Global Address Configuration - The host configures itself with its globally unique Internet address. The address comprises of a network prefix provided by the router together with the device identifier.


Neighbor Discovery

The Neighbor Discovery Protocol or NDP in the IPv6 is an improvement over the Internet Control Message Protocol (ICMP). It is essentially a messaging protocol that facilitates the discovery of neighboring devices over a network. The NDP uses two kinds of addresses: unicast addresses and multicast addresses. The Neighbor Discovery protocol performs nine specific tasks that are divided into three functional groups:

IPv6

Advantages of Stateless Auto Configuration

1.Doesn't require support of a DHCP server - Stateless Auto Configuration does away with the need of a DHCP server to allocate IP addresses to the individual nodes connected to the Local Area Network (LAN).

2. Allows hot plugging of network devices - The network devices can be 'hot-plugged' to the Internet. Since the devices can configure their own IP addresses, there is no need for manual configuration of the network devices. The devices can be simply connected to the network and they automatically configure themselves to be used over an IPv6 network.

3.Suitable for applications requiring secure connection without additional intermediaries in the form of a proxy or a DHCP server - Some of the modern day applications such as teleconferencing require a fast and secure connection sans any intermediary nodes that tend to slow down the communication process. Stateless Auto Configuration helps meet such requirements by removing the intermediary proxy or DHCP servers and thereby facilitating the communication process for such applications requiring high-speed data transfers.

4.Cost effective - By facilitating the networking potential of individual nodes and doing away with the requirement of proxy or DHCP servers, Stateless Auto Configuration offers cost effective means to connect the various network devices to the Internet.

5.Suitable for wireless networks - Stateless auto configuration is most suited to the wireless environment where the physical network resources are spatially scattered within a geographical area. By allowing direct hot plugging to the network, it reduces an additional link in the wireless network.

Applications of Stateless Auto Configuration

The Stateless Auto Configuration feature was long awaited to facilitate effortless networking of various devices to the Internet. The feature assumes even greater significance for use over the wireless networks. It allows the various devices to access the network from anywhere within a 'hotspot'. Stateless Auto Configuration finds diverse applications in networking electronic devices such as televisions, washing machines, refrigerators, microwaves etc. to the Internet. The ease of network connectivity through 'hot plugging' of such devices will usher in a new era of convergence where majority of the electronic devices will be connected to the Internet.