Configuring The Binding Table Timeout; Synchronizing The Binding Table - Alcatel-Lucent OmniSwitch 6850-48 Network Configuration Manual

Configuring DHCP Relay

Configuring the Binding Table Timeout

The contents of the DHCP Snooping binding table resides in the switch memory. In order to preserve table
entries across switch reboots, the table contents is automatically saved to the dhcpBinding.db file located
in the /flash/switch directory.
Note. Do not manually change the dhcpBinding.db file. This file is used by DHCP Snooping to preserve
and maintain binding table entries. Changing the file name or contents can cause problems with this func-
tionality or with the DHCP Snooping application itself.
The amount of time, in seconds, between each automatic save is referred to as the binding table timeout
value. By default, the timeout value is 300 seconds. To configure this value, use the
ip helper dhcp-snooping binding timeout
out value to 1500 seconds:
-> ip helper dhcp-snooping binding timeout 1500
Each time an automatic save is performed, the dhcpBinding.db file is time stamped.

Synchronizing the Binding Table

To synchronize the contents of the dhcpBinding.db file with the binding table contents that resides in
memory, use the ip helper dhcp-snooping binding action
parameters: purge and renew. Use the purge parameter to clear binding table entries in memory and the
renew parameter to populate the binding table with the contents of the dhcpBinding.db file. For example:
-> ip helper dhcp-snooping binding action purge
-> ip helper dhcp-snooping binding action renew
Synchronizing the binding table is only done when this command is used. There is no automatic trigger-
ing of this function. In addition, it is important to note that synchronizing the binding table loads dhcp-
Binding.db file contents into memory. This is the reverse of saving the binding table contents in memory
to the dhcpBinding.db file, which is done at automatic time intervals as defined by the binding table
timeout value. See "Configuring the Binding Table Timeout" on page 31-23
Binding Table Retention
When the binding table is synchronized with the contents of the dhcpBinding.db file, any table entries
with a MAC address that no longer appears in the MAC address table are cleared from the binding table.
To retain these entries regardless of their MAC address table status, use the
binding persistency
-> ip helper dhcp-snooping binding persistency enable
When binding table retention is enabled, enries remain in the table for the term of their DHCP lease and
are not removed even when the MAC address for the entry is cleared from the MAC address table.
To disable binding table retention, use the following command:
-> ip helper dhcp-snooping binding persistency disable
Use the show ip helper
OmniSwitch AOS Release 6 Network Configuration Guide
command. For example, the following command sets the time-
command. For example:
command to determine the status of binding table retention.
Configuring DHCP Security Features
command. This command provides two
for more information.
ip helper dhcp-snooping
September 2009 page 31-23