CLI Reference Guide-R04

Chapter 31 | IP Interface Commands
ND Snooping
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Related Commands
show mac-address-table (504)
ND Snooping
Neighbor Discover (ND) Snooping maintains an IPv6 prefix table and user address
binding table. These tables can be used for stateless address auto-configuration or
for address filtering by IPv6 Source Guard.
ND snooping maintains a binding table in the process of neighbor discovery. When
it receives an Neighbor Solicitation (NS) packet from a host, it creates a new
binding. If it subsequently receives a Neighbor Advertisement (NA) packet, this
means that the address is already being used by another host, and the binding is
therefore deleted. If it does not receive an NA packet after a timeout period, the
binding will be bound to the original host. ND snooping can also maintain a prefix
table used for stateless address auto-configuration by monitoring Router
Advertisement (RA) packets sent from neighboring routers.
ND snooping can also detect if an IPv6 address binding is no longer valid. When a
binding has been timed out, it checks to see if the host still exists by sending an NS
State The following states are used for dynamic entries:
I1 (Incomplete) - Address resolution is being carried out on the entry. A neighbor
solicitation message has been sent to the multicast address of the target, but it
has not yet returned a neighbor advertisement message.
I2 (Invalid) - An invalidated mapping. Setting the state to invalid dis-associates the
interface identified with this entry from the indicated mapping (RFC 4293).
R (Reachable) - Positive confirmation was received within the last ReachableTime
interval that the forward path to the neighbor was functioning. While in
REACHABLE state, the device takes no special action when sending packets.
S (Stale) - More than the ReachableTime interval has elapsed since the last
positive confirmation was received that the forward path was functioning. While
in STALE state, the device takes no action until a packet is sent.
D (Delay) - More than the ReachableTime interval has elapsed since the last
positive confirmation was received that the forward path was functioning. A
packet was sent within the last DELAY_FIRST_PROBE_TIME interval. If no
reachability confirmation is received within this interval after entering the DELAY
state, the switch will send a neighbor solicitation message and change the state
to PROBE.
P1 (Probe) - A reachability confirmation is actively sought by resending neighbor
solicitation messages every RetransTimer interval until confirmation of
reachability is received.
U (Unknown) - Unknown state.
The following states are used for static entries:
I1 (Incomplete)-The interface for this entry is down.
R (Reachable) - The interface for this entry is up. Reachability detection is not
applied to static entries in the IPv6 neighbor discovery cache.
P2 (Permanent) - Indicates a static entry.
Interface VLAN interface from which the address was reached.
Table 182: show ipv6 neighbors - display description (Continued)
Field Description