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10 DHCP Snooping Release Note

Software Version 2.7.6

C613-10462-00 REV A

Lease structure Each lease in the database holds the following information:

■ the MAC address of the client device

■ the IP address that was allocated to that client

■ time until expiry

■ VLAN to which the client is attached

■ port to which the client is attached

Database structure The binding database is split into three sections:

■ current valid entries

■ entries with client lease but no listener.

Listeners are processes within the switch that use the information

contained in entries. The Classifier module is the listener that receives

information from DHCP snooping.

■ entries with no client lease and no listeners.

For more information about these database sections, see the show

dhcpsnooping database command on page 26.

Adding static entries Although the switch dynamically adds information to the binding database,

you can also optionally add static entries to the database. This is typically used

to add a DHCP snooping entry for a client that has a preconfigured IP address

on an untrusted port. To do this, use the command:

add dhcpsnooping binding interface=vlan ip=ipadd

port=port-number

Configuring a check

interval

You can configure a check interval, in seconds, for the binding database. This

determines how often dynamic entries are checked for expiration. Expired

entries are automatically deleted from the database.

Static entries defined with the add dhcpsnooping binding command on

page 14 are not checked.

To configure a check interval for the binding database, use the command:

set dhcpsnooping checkinterval=1..3600

The switch receives expiry information with the client lease. Entries expire

when the time left to expiry is 0 seconds.

All dynamic entries remaining in the database after each check are written to

the bindings.dsn file. Whenever DHCP snooping is enabled using the enable

dhcpsnooping command on page 18, the DHCP snooping binding database is

recreated. Any entries that are still current are added to the database.

To view the current DHCP snooping binding database, use the command:

show dhcpsnooping database

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Allied Telesis AT-8648T/2SP Guide d'installation Page 10