Neighbor Discovery Protocol

NDP helps IPv6 devices find nearby routers and neighbours

Neighbour Discovery Protocol (NDP)

NDP is a protocol that helps with IPv6. It is a collection of tools that are critical to IPv6 operating correctly.

NDP has several jobs. One is is to resolve IP addresses to MAC addresses. In IPv4, this was done by ARP, The Address Resolution Protocol. In IPv6, ARP had to be replaced, as it relies on broadcasts. IPv6 does not support broadcasts.

It also discovers IPv6 routers and other devices in the local network. This is useful if a client is trying to find a default gateway. This also applies to the discovery of network prefixes. This is clearly useful for assigning IP addresses to clients.

And it includes a tool called Duplicate Address Detection. This checks if there are any IP conflicts when assigning a new IP address.

At the core of NDP is ICMP version 6. ICMP is the protocol that sends messages between devices. This includes ping, and sometimes traceroute.

The four primary messages used by NDP and ICMPv6 are:

  • Router Solicitation
  • Router Advertisement
  • Neighbour Solicitation
  • Neighbour Advertisement