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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter22 Configuring DHCP Features and IP Source Guard Features
Configuring DHCP Snooping
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 stack master. When a new switch joins the stack, the switch receives
the DHCP snooping configuration from the stack master. When a member leaves the stack, all DHCP
snooping address bindings associated with the switch age out.
All snooping statistics are generated on the stack master. If a new stack master is elected, the statistics
counters reset.
When a stack merge occurs, all DHCP snooping bindings in the stack master are lost if it is no longer
the stack master. With a stack partition, the existing stack master is unchanged, and the bindings
belonging to the partitioned switches age out. The new master of the partitioned stack begins processing
the new incoming DHCP packets. For more information about switch stacks, see Chapter5, “Managing
Switch Stacks.”
Configuring DHCP Snooping
These sections contain this configuration information:
Default DHCP Snooping Configuration, page22-10
DHCP Snooping Configuration Guidelines, page22-10
Configuring the DHCP Relay Agent, page22-11
Specifying the Packet Forwarding Address, page22-12
Enabling DHCP Snooping and Option 82, page22-13
Enabling DHCP Snooping on Private VLANs, page22-15
Enabling the Cisco IOS DHCP Server Database, page 22-15
Enabling the DHCP Snooping Binding Database Agent, page22-15