The IPv6 neighbor discovery process uses ICMP messages and solicited-node multicast addresses to determine the link-layer address of a neighbor on the same network (local link), verify the reachability of a neighbor, and track neighboring devices.
The IPv6 static cache entry for neighbor discovery feature allows static entries to be made in the IPv6 neighbor cache. Static routing requires an administrator to manually enter IPv6 addresses, subnet masks, gateways, and corresponding Media Access Control (MAC) addresses for each interface of each device into a table. Static routing enables more control but requires more work to maintain the table. The table must be updated each time routes are added or changed
Neighbor discovery uses ICMPv6 messages, originated from node on link local with hop limit of 255,Consists of IPv6 header, ICMPv6 header, neighbor discovery header, and neighbor discovery options Five neighbor discovery messages
- Router solicitation (ICMPv6 type 133)
- Router advertisement (ICMPv6 type 134)
- Neighbor solicitation (ICMPv6 type 135)
- Neighbor advertisement (ICMPv6 type 136)
- Redirect (ICMPV6 type 137)
Router Solicitation and Advertisement
Router solicitations (RS) are sent by booting nodes to request RAs for configuring the interfaces. Routers send periodic Router Advertisements (RA) to the all-nodes multicast address.
Neighbor Solicitation and Advertisement
After receiving the neighbor solicitation message, the destination node replies by sending a neighbor advertisement message, which has a value of 136 in the Type field of the ICMP packet header, on the local link. The source address in the neighbor advertisement message is the IPv6 address of the node (more specifically, the IPv6 address of the node interface) sending the neighbor advertisement message. The destination address in the neighbor advertisement message is the IPv6 address of the node that sent the neighbor solicitation message. The data portion of the neighbor advertisement message includes the link-layer address of the node sending the neighbor advertisement message.