TYPE DHCP-SNOOPING VERSION 1 BEGIN ... ... END Each entry in the file is tagged with a checksum value that the switch uses to verify the entries when it reads the file. The initial-checksum entry on the first line distinguishes entries associated with the latest file update from entries associated with a previous file update. This is an example of a binding file:
3ebe1518 TYPE DHCP-SNOOPING VERSION 1 BEGIN 10.1.1.1 512 001.0001.0005 3EBE2881 Gi1/1 e5e1e733 10.1.1.1 512 001.0001.0002 3EBE2881 Gi1/1 4b3486ec 10.1.1.1 1536 001.0001.0004 3EBE2881 Gi1/1 f0e02872 10.1.1.1 1024 001.0001.0003 3EBE2881 Gi1/1 ac41adf9 10.1.1.1 1 001.0001.0001 3EBE2881 Gi1/1 34b3273e END When the switch starts and the calculated checksum value equals the stored checksum value, the switch reads entries from the binding file and adds the bindings to its DHCP snooping binding database. The switch ignores an entry when one of these situations occurs: • The switch reads the entry and the calculated checksum value does not equal the stored checksum value.
The entry and the ones following it are ignored. • An entry has an expired lease time (the switch might not remove a binding entry when the lease time expires). • The interface in the entry no longer exists on the system. • The interface is a routed interface or a DHCP snooping-trusted interface. DHCP Snooping and Switch Stacks DHCP snooping is managed on the active switch. When a new switch joins the stack, the switch receives the DHCP snooping configuration from the active switch. When a member leaves the stack, all DHCP snooping address bindings associated with the switch age out. All snooping statistics are generated on the active switch.
If a new active switch is elected, the statistics counters reset. When a stack merge occurs, all DHCP snooping bindings in the active switch are lost if it is no longer the active switch. With a stack partition, the existing active switch is unchanged, and the bindings belonging to the partitioned switches age out. The new active switch of the partitioned stack begins processing the new incoming DHCP packets. Configuring DHCP DHCP Snooping and Switch Stacks Configuring DHCP 8