19-3
Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-09
Chapter 19 Configuring DHCP Features
Configuring DHCP Features
• The DHCP server unicasts the reply to the switch if the request was relayed to the server by the
switch. When the client and server are on the same subnet, the server broadcasts the reply. The
switch verifies that it originally inserted the option-82 data by inspecting the remote ID and possibly
the circuit ID fields. The switch removes the option-82 field and forwards the packet to the switch
port that connects to the DHCP client that sent the DHCP request.
Configuring DHCP Features
These sections describe how to configure DHCP snooping and option 82 on your switch:
• Default DHCP Configuration, page 19-3
• DHCP Snooping Configuration Guidelines, page 19-3
• Upgrading from a Previous Software Release, page 19-4
• Enabling DHCP Snooping and Option 82, page 19-4
• Enabling the DHCP Relay Agent and Option 82, page 19-6
• Validating the Relay Agent Information Option 82, page 19-6
• Configuring the Reforwarding Policy, page 19-7
• Specifying the Packet Forwarding Address, page 19-7
Default DHCP Configuration
Table 19-1 shows the default DHCP configuration.
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.
Table 19-1 Default DHCP Configuration
Feature Default Setting
DHCP snooping enabled globally Disabled
DHCP snooping information option Enabled
DHCP relay information option Enabled
DHCP snooping limit rate None configured
DHCP snooping trust Untrusted
DHCP snooping VLAN Disabled
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