CLI Reference Guide-R01

Chapter 30 | IP Interface Commands
ND Snooping
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Example
The following shows all neighbor discovery IPv6 prefixes for VLAN 1:
Console#show ipv6 nd prefix vlan 1
Ipv6 Neighbor Discovery Prefix Information.
VLAN Name : DefaultVlan
IPv6 Prefix : 2011:dbf::/35
Valid Lifetime : 2592000
Preferred Lifetime : 604800
On-link Flag : On
Autonomous Flag : On
Console#
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ND snooping can also detect if an IPv6 address binding is no longer valid.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.
Table 168: 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