Explanation/Reference:
Explanation:
The Neighbor Discovery Protocol (NDP, ND)[1] is a protocol in the Internet protocol suite used with Internet Protocol Version 6 (IPv6). It operates at the Network Layer of the Internet model (RFC 1122), and is responsible for gathering various information required for internet communication, including the configuration of local connections and the domain name servers and gateways used to communicate with more distant systems.
The Inverse Neighbor Discovery (IND) protocol extension (RFC 3122) allows nodes to determine and advertise an IPv6 address corresponding to a given link-layer address, similar to Reverse ARP for IPv4.
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NDP defines five ICMPv6 packet types for the purpose of router solicitation, router advertisement, neighbor solicitation, neighbor advertisement, and network redirects.[2]
Router Solicitation (Type 133)
Hosts inquire with Router Solicitation messages to locate routers on an attached link.[3] Routers which forward packets not addressed to them generate Router Advertisements immediately upon receipt of this message rather than at their next scheduled time.
Router Advertisement (Type 134)
Routers advertise their presence together with various link and Internet parameters either periodically, or in response to a Router Solicitation message.
Neighbor Solicitation (Type 135)
Neighbor solicitations are used by nodes to determine the link layer address of a neighbor, or to verify that a neighbor is still reachable via a cached link layer address.
Neighbor Advertisement (Type 136)
Neighbor advertisements are used by nodes to respond to a Neighbor Solicitation message.
Redirect (Type 137)
Routers may inform hosts of a better first hop router for a destination.