IPv6 Neighbor Discovery

It is a protocol which replaces IPv4 Address Resolution Protocol (ARP) that locates the hardware address for a host. IPv6 also adds new networking features to an infrastructure. Making it capable of recognizing a new standard of IPv6 addresses and technologies.

IPv6 Neighbor Discovery uses Internet Control Message Protocol or ICMPv6.  It is a new version of the ICM protocol that is integrated with IPv6 architecture.  ICMPv6 offers a framework for integrating future changes in addition to performing the standard functions of ICMP. This for diagnostics and error reporting.

IPv6 Neighbor Discovery is also used to find the link/layer address of a neighbor host. It also, locate neighboring routers, track neighbor reachability, send network data from routers to hosts, and map IP addresses. This to Mac addresses, to name a few purposes.

How it Works

IPv6 Neighbor Discovery works through the use of two technologies that are commonly known as Neighbor Solicitation and Neighbor Advertisement.  These technologies are used in a series of steps. Which are deployed in order for a host to discover a neighbor.

The first step for Neighbor Discovery is to determine whether or not you have an authentic unique address.   Host 1 sends out a Neighbor Solicitation using an IP address which Host 1 wants to use as a destination.  This process is known as a tentative address.  Before the address is sent out the source address of Host 1 is set to a null field known as an unspecified address. If the address is strictly unique there will be no response to Host 1.

Host 2

If Host 2 is already using the address that Host 1 would like to use. Host 2 will respond with what is known as a Neighbor Advertisement in the form of a multicast which is a method of forwarding IP data to multiple recipients.  Due to the fact that Host 1 used an unspecified address or null address as its source, Host 2 cannot respond directly to Host 1 which is the reason for the multicast.  This is an indication that the particular address is already in use which requires Host 1 to modify the source address.

Assuming there is now a unique address, the Neighbor Discovery process can begin. As an example of initiating the Neighbor Discovery process, Host 1 sends out the multicast Neighbor Solicitation message to all hosts with an ICMP value of 125 (as an example). Host 2 then responds to the link local address of Host 1 with a Neighbor Advertisement message having an ICMP value of 126.

Then sends out a Neighbor Solicitation message to all hosts with an ICMP value of 125.  Host 1 then responds to the link local address of Host B with a Neighbor Advertisement having an ICP value of 126. Host 1 and Host 2 can now exchange packets on this link and are in a reachable state.

Why the Protocol is Important

The new IPv6 protocol marks the beginning of a new generation of the Internet. The IP addresses distributed under the old IPv4 standard are close to being depleted.  Unique IP addresses are necessary for two machines connected to the Internet to communicate with one another.

IPv6 not only increases the number of available IP addresses, the protocol also provides for the improved use of modern technologies and hardware, increased efficiency when it comes to routing, and better support for mobile device usage.  IPv6 also offers improved security features not present with the IPv4 standard such as IPsec, end-to-end connectivity with increased reliance on Network Address Translation for easier configuration of encrypted networks, and a much larger number of IP addresses which allows for better address assignment, to name a few enhancements.

ARP

When compared to ARP and IPv4 related protocols, IPv4 typically does not have a specified protocol for detecting neighbor unreachability. It also enables its routers to advertise a Maximum Transmission Unit (MTU) to enable hosts to use the link where IPv4 hosts that use the same network may have varying MTUs.

Other benefits of IPv6 Neighbor Discover are the capability to identify half-link failures through the use of neighbor unreachability detection. Which avoids the transmission of traffic to neighbors when two-way connectivity is non-existent. Additionally, the unreachability detection enhances packet delivery in the case of failing routers or partially failing and partitioned links.  ARP and IPv4 have no capability for neighbor unreachability.  Plus, the probability is higher of mobile nodes losing connectivity when moving off a local network due to older ARP caches.

For the above reasons, more companies are seeking to make their services available on IPv6 configurations. Because it means users will not have to be concerned about complicated setup or configurations. Instead, they can simply connect their network devices, and access the Internet. Without worrying about compatibility or the type of networking technology their device uses.

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