Configuring Switching Information 401– Local — Select the Local check box to store the DHCP binding database in the flash memory onthe switch .– Remote — Check the Remote check box to store the DHCP binding database on a remoteserver.• Remote IP Address — Enter the Remote IP address on which the snooping database will be storedwhen the Remote check box is selected.• Remote File Name — Enter the Remote filename to store the database when the Remote check box isselected.• Write Delay — Enter the maximum write time to write the database into the local or remote location.The write delay range is 15 to 86400 seconds.Configuring DHCP Snooping With CLI CommandsFor information about the CLI commands that perform this function, refer to the following chapter intheCLI Reference Guide:• DHCP Snooping CommandsDHCP Snooping Static Bindings ConfigurationUse the DHCP Snooping Static Bindings Configuration page to add static DHCP bindings to thebinding database.The DHCP snooping application uses DHCP messages to build and maintain the binding’s database.The binding’s database only includes data for clients on untrusted ports. DHCP snooping creates atentative binding from DHCP DISCOVER and REQUEST messages. Tentative bindings tie a client to aport (the port where the DHCP client message was received). Tentative bindings are completed whenDHCP snooping learns the client’s IP address from a DHCP ACK message on a trusted port. DHCPsnooping removes bindings in response to DECLINE, RELEASE, and NACK messages. The DHCPsnooping application ignores the ACK messages as a reply to the DHCP Inform messages received ontrusted ports. You can also enter static bindings into the binding database.The DHCP binding database is persisted on a configured external server or locally in flash, depending onthe user configuration. A row-wise checksum is placed in the text file that is going to be stored in theremote configured server. On reloading, the switch reads the configured binding file to build the DHCPsnooping database. When the switch starts and the calculated checksum value equals the storedchecksum, the switch reads entries from the binding file and populates the binding database. Achecksum failure or a connection problem to the external configured server will cause the switch to loosethe bindings and will cause a host’s data loss if DAI is enabled.When a switch learns of new bindings or when it loses bindings, the switch immediately updates theentries in the database. The switch also updates the entries in the binding file. The frequency at whichthe file is updated is based on a configurable delay, and the updates are batched.
