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Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter 22 Configuring DHCP Features and IP Source Guard
Configuring DHCP Features
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 Chapter 5, “Managing
Switch Stacks.”
Configuring DHCP Features
These sections contain this configuration information:
• Default DHCP Configuration, page 22-8
• DHCP Snooping Configuration Guidelines, page 22-9
• Configuring the DHCP Server, page 22-10
• DHCP Server and Switch Stacks, page 22-10
• Configuring the DHCP Relay Agent, page 22-11
• Specifying the Packet Forwarding Address, page 22-11
• Enabling DHCP Snooping and Option 82, page 22-12
• Enabling DHCP Snooping on Private VLANs, page 22-14
• Enabling the Cisco IOS DHCP Server Database, page 22-14
• Enabling the DHCP Snooping Binding Database Agent, page 22-14
Default DHCP Configuration
Table 22-1 shows the default DHCP configuration.
Table 22-1 Default DHCP Configuration
Feature Default Setting
DHCP server Enabled in Cisco IOS software, requires
configuration
1
DHCP relay agent Enabled
2
DHCP packet forwarding address None configured
Checking the relay agent information Enabled (invalid messages are dropped)
2
DHCP relay agent forwarding policy Replace the existing relay agent information
2
DHCP snooping enabled globally Disabled
DHCP snooping information option Enabled