C
HAPTER
45
| IP Interface Commands
ND Snooping
– 1430 –
RELATED COMMANDS
show mac-address-table (1061)
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ND snooping can also detect if an IPv6 address binding is no longer valid.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 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.
This section describes commands used to configure ND Snooping.
State
(continued)
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 201: show ipv6 neighbors - display description (Continued)
Field Description
Table 202: ND Snooping Commands
Command Function Mode
ipv6 nd snooping Enables ND snooping globally or on a specified VLAN
or range of VLANs
GC
ipv6 nd snooping
auto-detect
Enables automatic validation of binding table entries
by periodically sending NS messages and awaiting
NA replies
GC
ipv6 nd snooping auto-
detect retransmit count
Sets the number of times to send an NS message to
determine if a binding is still valid
GC
ipv6 nd snooping auto-
detect retransmit interval
Sets the interval between sending NS messages to
determine if a binding is still valid
GC
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