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31-2
Cisco ASA 5500 Series Configuration Guide using ASDM
Chapter 31 Configuring IPv6 Neighbor Discovery
Information About IPv6 Neighbor Discovery
nodes use the protocol to actively keep track of which neighbors are reachable and which are not, and to
detect changed link-layer addresses. When a router or the path to a router fails, a host actively searches
for functioning alternates.
This section includes the following topics:
• Neighbor Solicitation Messages, page 31-2
• Neighbor Reachable Time, page 31-3
• Router Advertisement Messages, page 31-3
• Static IPv6 Neighbors, page 31-4
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. Figure 31-1 shows the neighbor solicitation and response process.
Figure 31-1 IPv6 Neighbor Discovery—Neighbor Solicitation Message
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.
132958
A and B can now exchange
packets on this link
ICMPv6 Type = 135
Src = A
Dst = solicited-node multicast of B
Data = link-layer address of A
Query = what is your link address?
ICMPv6 Type = 136
Src = B
Dst = A
Data = link-layer address of B