Neighbor Discovery Protocol

Neighbor Discovery Protocol (NDP) is a protocol used with IPv6.

It has various functions, and one of those functions is to replace ARP, which is no longer used in IPv6.

The ARP-like function of NDP uses ICMPv6 and solicited-node multicast addresses to learn the MAC address of other hosts.

Two messages types are used:

1. Neighbor Solicitation (NS) = ICMPv6 Type 135

2. Neighbor Advertisement (NA) = ICMPv6 Type 136

Neighbor Solicitation (NS)

• Source IP: R1 G0/0 IP

• Destination IP: R2 solicited-node multicast address

• Source MAC: R1 G0/0 MAC

• Destination MAC: Multicast MAC based on R2's solicited-node address

Neighbor Advertisement (NA)

• Source IP: R2 G0/0 IP

• Destination IP: R1 G0/0 IP

• Source MAC: R2 G0/0 MAC

• Destination MAC: R1 G0/0 MAC

IPv6 Neighbor Table

Router Solicitation / Advertisement

Another function of NDP allows hosts to automatically discover routers on the local network.

Two messages are used for this process:

1. Router Solicitation (RS) = ICMPv6 Type 133

   1. Sent to multicast address FF02::2 (all routers).

   2. Asks all routers on the local link to identify themselves.

   3. Sent when an interface is enabled/host is connected to the network.

2. Router Advertisement (RA) = ICMPv6 Type 134

   1. Sent to multicast address FF02::1 (all nodes).

   2. The router announces its presence, as well as other information about the link.

   3. These messages are sent in response to RS messages.

   4. They are also sent periodically, even if the router hasn't received an RS.