Chapter 30
| IP Interface Commands
ND Snooping
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If an NS message is received on an untrusted interface, and the address
prefix does not match any entry in the prefix table, it drops the packet.
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If the message does match an entry in the prefix table, it adds an entry to
the dynamic user binding table after a fixed delay, and forwards the packet.
Each entry in the dynamic binding table includes the link-layer address,
IPv6 address, lifetime, as well as the VLAN and port interface which received
the message.
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If an RA message is received in response to the original NS message
(indicating a duplicate address) before the dynamic binding timeout period
expires, the entry is deleted. Otherwise, when the timeout expires, the
entry is dropped if the auto-detection process is not enabled.
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If the auto-detection process is enabled, the switch periodically sends an
NS message to determine is the client still exists. If it does not receive an RA
message in response after the configured timeout, the entry is dropped. If
the switch receives an RA message before the timeout expires, it resets the
lifetime for the dynamic binding, and the auto-detection process resumes.
Example
This example enables ND snooping globally and on VLAN 1.
Console(config)#ipv6 nd snooping
Console(config)#ipv6 nd snooping vlan 1
Console(config)#
ipv6 nd snooping
auto-detect
This command enables automatic validation of dynamic user binding table entries
by periodically sending NS messages and awaiting NA replies. Use the no form to
disable this feature.
Syntax
[no] ipv6 nd snooping auto-detect
Default Setting
Disabled
Command Mode
Global Configuration
Command Usage
If auto-detection is enabled, the switch periodically sends an NS message to
determine is a client listed in the dynamic binding table still exists. If it does not
receive an RA message in response after the configured timeout, the entry is
dropped. If the switch receives an RA message before the timeout expires, it resets
the lifetime for the dynamic binding, and the auto-detection process resumes.
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