Administrator Guide

Neighbor Discovery Protocol (NDP)
The neighbor discovery protocol for IPv6 is defined in RFC 2461 as part of the Stateless Address Autoconfiguration protocol. It
replaces the Address Resolution Protocol used with IPv4. NDP defines mechanisms for solving the following problems:
● Router discovery — hosts can locate routers residing on a link
● Prefix discovery — hosts can discover address prefixes for the link
● Parameter discovery
● Address autoconfiguration — configuration of addresses for an interface
● Address resolution — mapping from IP address to link-layer address
● Next-hop determination
● Neighbor unreachability detection (NUD) — determine that a neighbor is no longer reachable on the link.
● Duplicate address detection (DAD) — allow a node to check whether a proposed address is already in use.
● Redirect — the router can inform a node about a better first-hop.
NDP uses the following five ICMPv6 packet types in its implementation:
● Router Solicitation
● Router Advertisement
● Neighbor Solicitation
● Neighbor Advertisement
● Redirect
Topics:
• clear ipv6 neighbors
• ipv6 neighbor
• show ipv6 neighbors
• IPv6 Router Advertisement (RA) Guard
clear ipv6 neighbors
Delete all entries in the IPv6 neighbor discovery cache or neighbors of a specific interface. Static entries are not removed using
this command.
Syntax
clear ipv6 neighbors [vrf vrf-name] [ipv6-address | interface]
Parameters
vrf vrf-name (OPTIONAL) Enter the keyword vrf followed by the name of the VRF to clear the
neighbor corresponding to that VRF.
NOTE: If you do not specify this option, the neighbors in the default VRF are
cleared.
ipv6-address Enter the IPv6 address of the neighbor in the x:x:x:x::x format to remove a specific
IPv6 neighbor.
NOTE: The :: notation specifies successive hexadecimal fields of zero.
interface
interface
To remove all neighbor entries learned on a specific interface, enter the keyword
interface then the interface type and slot/port or number information of the
interface:
● For a 1-GigabitEthernet interface, enter the keyword GigabitEthernet then
the slot/port information.
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992 Neighbor Discovery Protocol (NDP)