TCP/IPv6 Configuration and Management Manual (G06.29+, H06.03+, J06.03+)

IPv6 Fundamentals
HP NonStop TCP/IPv6 Configuration and Management Manual—524523-012
A-15
Neighbor Discovery Protocol
advertisements contain prefixes that are used for on-link determination and/or
address configuration, a suggested hop limit value, and so on.

Neighbor solicitation
Sent by a node to determine the link-layer address of a neighbor, or to verify that a
neighbor is still reachable through a cached link-layer address. Neighbor
solicitations are also used for duplicate address detection.

Neighbor advertisement
A response to a neighbor solicitation message. A node can also send unsolicited
neighbor advertisements to announce a link-layer address change.

Redirect
Used by routers to inform hosts of a better first hop for a destination.
On multicast-capable links, each router periodically multicasts a router advertisement
packet announcing that router’s availability. A host receives router advertisements from
all routers, building a list of default routers. Routers generate router advertisements
frequently enough that hosts learn of their presence within a few minutes, but not
frequently enough to rely on an absence of advertisements to detect router failure; a
separate neighbor-unreachability detection algorithm provides failure detection.
Router advertisements contain a list of prefixes used for on-link determination and
autonomous address configuration; flags associated with the prefixes specify the
intended uses of a particular prefix. Hosts use the advertised on-link prefixes to build
and maintain a list that is used in deciding when a packet's destination is on-link or
beyond a router. Note that a destination can be on-link although it is not covered by
any advertised on-link prefix. In such cases, a router can send a redirect informing the
sender that the destination is a neighbor.
Router advertisements (and per-prefix flags) allow routers to inform hosts how to
perform address autoconfiguration. For example, routers can specify whether hosts
should use stateful (DHCPv6) (not supported by NonStop TCP/IPv6) or autonomous
(stateless) address configuration.
Router advertisement messages also contain Internet parameters such as the hop limit
that hosts should use in outgoing packets and, optionally, link parameters such as the
link MTU. These parameters facilitate centralized administration of critical parameters
that can be set on routers and automatically propagated to all attached hosts.
Nodes accomplish address resolution by multicasting a neighbor solicitation that asks
the target node to return its link-layer address. Neighbor solicitation messages are
multicast to the solicited-node multicast address of the target address. The target
returns its link-layer address in a unicast neighbor advertisement message. A single
request-response pair of packets is sufficient for both the initiator and the target to
resolve each other's link-layer addresses; the initiator includes its link-layer address in
the neighbor solicitation.