User Manual
UMN:CLI
V8102
279
8.2
IPv6 Neighbor Discovery
Neighbor discovery (ND) is specified in RFC 2464. ND combines Address Resolution Pro-
tocol (ARP) and ICMP router discovery and Redirect. With IPv4, we have no means to
detect whether or not a neighbor is reachable. With ND protocol, a neighbor unreachabil-
ity detection mechanism has been defined.
IPv6 nodes use neighbor discovery for the following purposes:
- To determine Layer 2 addresses of nodes on the same link
- To find neighboring routers that can forward their packets
- To keep track of which neighbor are reachable and which are not, and detect changed
link-layer addresses
The neighbor discovery protocol consists of five ICMP messages:
•
Router Solicitation / Router Advertisement (RS & RA)
The routers send out Router Advertisement (RA) message in regular intervals. The
hosts can request RA message by issuing a Router Solicitation message.
RA message contains the information of link prefixes, link MTU, specific routers, and
duration.
•
Neighbor Solicitation / Neighbor Advertisement (NS & NA)
These messages fulfill the functions that the link-layer address resolution in IPv4
and the neighbor unreachability detection mechanism. The IPv6 host sends Neighbor
Solicitation message to discover the link-layer address of an on-link IPv6 node. IPv6
node sends the Neighbor Advertisement message in response to a NS and sends
unsolicited NA to inform neighboring nodes of link-layer addresses.
•
ICMP redirect message
IPv6 router sends ICMP redirect message to inform an originating host of a better
first-hop address for specific destination.
8.2.1
Stateful Auto Configuration
Router Advertisements sent from this interface have the Managed Address Configuration
Flag or not. It decides that the hosts are thus permitted to use IPv6 stateless autoconfigu-
ration to create global unicast addresses for themselves. This means that the attached
hosts should use stateful autoconfiguration to obtain addresses if the flag is set.
To set the managed address configuration flag in IPv6 RA messages, use the following
command.
Command
Mode
Description
ipv6 nd managed-config-flag
Interface
[VLAN/MGMT
/LO]
Sets the managed address configuration flag in RA.
no ipv6 nd managed-config-flag
Clears the managed address configuration flag from
RA. (default)