Cisco ASA Series Cli Configuration Manual page 730

Information About IPv6 Neighbor Discovery
Neighbor Solicitation Messages
Neighbor solicitation messages (ICMPv6 Type 135) are sent on the local link by nodes attempting to
discover the link-layer addresses of other nodes on the local link. The neighbor solicitation message is
sent to the solicited-node multicast address. The source address in the neighbor solicitation message is
the IPv6 address of the node sending the neighbor solicitation message. The neighbor solicitation
message also includes the link-layer address of the source node.
After receiving a neighbor solicitation message, the destination node replies by sending a neighbor
advertisement message (ICPMv6 Type 136) on the local link. The source address in the neighbor
advertisement message is the IPv6 address of the node sending the neighbor advertisement message; the
destination address 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.
After the source node receives the neighbor advertisement, the source node and destination node can
communicate.
Neighbor solicitation messages are also used to verify the reachability of a neighbor after the link-layer
address of a neighbor is identified. When a node wants to verifying the reachability of a neighbor, the
destination address in a neighbor solicitation message is the unicast address of the neighbor.
Neighbor advertisement messages are also sent when there is a change in the link-layer address of a node
on a local link. When there is such a change, the destination address for the neighbor advertisement is
the all-nodes multicast address.
Neighbor Reachable Time
The neighbor reachable time enables detecting unavailable neighbors. Shorter configured times enable
detecting unavailable neighbors more quickly, however, shorter times consume more IPv6 network
bandwidth and processing resources in all IPv6 network devices. Very short configured times are not
recommended in normal IPv6 operation.
Duplicate Address Detection
During the stateless autoconfiguration process, Duplicate Address Detection verifies the uniqueness of
new unicast IPv6 addresses before the addresses are assigned to interfaces (the new addresses remain in
a tentative state while Duplicate Address Detection is performed). Duplicate Address Detection is
performed first on the new link-local address. When the link-local address is verified as unique, then
Duplicate Address Detection is performed all the other IPv6 unicast addresses on the interface.
Duplicate Address Detection is suspended on interfaces that are administratively down. While an
interface is administratively down, the unicast IPv6 addresses assigned to the interface are set to a
pending state. An interface returning to an administratively up state restarts Duplicate Address Detection
for all of the unicast IPv6 addresses on the interface.
When a duplicate address is identified, the state of the address is set to DUPLICATE, the address is not
used, and the following error message is generated:
%ASA-4-325002: Duplicate address ipv6_address/MAC_address on interface
Cisco ASA Series CLI Configuration Guide
1-2
Chapter 1 Configuring IPv6 Neighbor Discovery