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| IP Interface Commands
ND Snooping
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ND S
NOOPING
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ND snooping can also detect if an IPv6 address binding is no longer valid.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 packet to the target host. If it receives an NA packet in
response, it knows that the target still exists and updates the lifetime of
the binding; otherwise, it deletes the binding.
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 REACH 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 re-sending
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.
VLAN VLAN interface from which the address was reached.
Table 217: show ipv6 neighbors - display description (Continued)
Field Description