Configuring DHCP Relay Configuring UDP Port Relay
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 21-21
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.
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 dhcp-snooping
binding timeout command. For example, the following command sets the timeout value to 1500 seconds:
-> 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 dhcp-snooping binding action command. This command provides two 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:
-> dhcp-snooping binding action purge
-> dhcp-snooping binding action renew
Synchronizing the binding table is only done when this command is used. There is no automatic triggering
of this function. In addition, it is important to note that synchronizing the binding table loads
dhcpBinding.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 21-21 for more information.
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 dhcp-snooping binding
persistency command. For example:
-> dhcp-snooping binding persistency enable
When binding table retention is enabled, entries 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:
-> dhcp-snooping binding persistency disable
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
functionality or with the DHCP Snooping application itself.
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