Setting the DHCPv4 binding database location

DHCPv4 snooping maintains a database of up to 8192 DHCP bindings on untrusted ports. Each binding consists of:

  • Client MAC address

  • Port number

  • VLAN identifier

  • Leased IP address

  • Lease time

You can configure the switch to store the bindings at a specific URL so they are not lost if the switch is rebooted. If the switch is rebooted, it reads its binding database from the specified location. To configure this location use this command.

Syntax 


dhcp-snooping database [file<tftp://<ip-address>/<ascii-string>>][delay<15-86400>][timeout<0-86400>]
no dhcp-snooping database [file<tftp://<ip-address>/<ascii-string>>][delay<15-86400>][timeout<0-86400>]
file

Specifies a file in Uniform Resource Locator (URL) format — “tftp://ip-address/ascii-string”. The maximum filename length is 63 characters.

delay

Specifies the number of seconds to wait before writing to the database. Default = 300 seconds.

timeout

Specifies the number of seconds to wait for the database file transfer to finish before returning an error. A value of zero (0) means retry indefinitely. Default = 300 seconds.

A message is logged in the system event log if the DHCP binding database fails to update. To display the contents of the DHCP snooping binding database, enter this command.

Syntax 


show dhcp-snooping binding
Showing DHCPv4 snooping binding database contents
NOTE:

If a lease database is configured, the switch drops all DHCPv4 packets until the lease database is read. This only occurs when the switch reboots and is completed quickly. If the switch is unable to read the lease database from the tftp server, it waits until that operation times out and then begins forwarding DHCP packets.