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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Chapter20 Configuring DHCP Features
Configuring DHCP Features
DHCP Snooping Configuration Guidelines
These are the configuration guidelines for DHCP snooping.
• You must globally enable DHCP snooping on the switch.
• DHCP snooping is not active until DHCP snooping is enabled on a VLAN.
• Before globally enabling DHCP snooping on the switch, make sure that the devices acting as the
DHCP server and the DHCP relay agent are configured and enabled.
• Before configuring the DHCP snooping information option on your switch, be sure to configure the
device that is acting as the DHCP server. For example, you must specify the IP addresses that the
DHCP server can assign or exclude, or you must configure DHCP options for these devices.
• If the DHCP relay agent is enabled but DHCP snooping is disabled, the DHCP option-82 data
insertion feature is not supported.
• If a switch port is connected to a DHCP server, configure a port as trusted by entering the ip dhcp
snooping trust interface configuration command.
• If a switch port is connected to a DHCP client, configure a port as untrusted by entering the no ip
dhcp snooping trust interface configuration command.
Configuring the DHCP Server
The Catalyst 2955 switch can act as a DHCP server. By default, the Cisco IOS DHCP server and relay
agent features are enabled on your switch but are not configured. These features are not operational.
For procedures to configure the switch as a DHCP server, refer to the “Configuring DHCP” section of
the “IP addressing and Services” section of the Cisco IOS IP and IP Routing Configuration Guide,
Release 12.1.
DHCP snooping trust Untrusted
DHCP snooping VLAN Disabled
1. The switch responds to DHCP requests only if it is configured as a DHCP server.
2. The switch relays DHCP packets only if the IP address of the DHCP server is configured on the SVI of the DHCP client.
Table 20-1 Default DHCP Configuration (continued)
Feature Default Setting