Chapter 22 Configuring DHCP Features and IP Source Guard

Configuring DHCP Features

Table 22-1

Default DHCP Configuration (continued)

 

 

 

Feature

 

Default Setting

 

 

DHCP snooping option to accept packets on

Disabled

untrusted input interfaces3

 

DHCP snooping limit rate

None configured

 

 

DHCP snooping trust

Untrusted

 

 

DHCP snooping VLAN

Disabled

 

 

DHCP snooping MAC address verification

Enabled

 

 

Cisco IOS DHCP server binding database

Enabled in Cisco IOS software, requires

 

 

configuration.

 

 

Note The switch gets network addresses and

 

 

configuration parameters only from a

 

 

device configured as a DHCP server.

 

 

DHCP snooping binding database agent

Enabled in Cisco IOS software, requires

 

 

configuration. This feature is operational only

 

 

when a destination is configured.

 

 

 

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.

3.Use this feature when the switch is an aggregation switch that receives packets with option-82 information from an edge switch.

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.

When you globally enable DHCP snooping on the switch, these Cisco IOS commands are not available until snooping is disabled. If you enter these commands, the switch returns an error message, and the configuration is not applied.

ip dhcp relay information check global configuration command

ip dhcp relay information policy global configuration command

ip dhcp relay information trust-all global configuration command

ip dhcp relay information trusted interface configuration command

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.

When configuring a large number of circuit IDs on a switch, consider the impact of lengthy character strings on the NVRAM or the flash memory. If the circuit-ID configurations, combined with other data, exceed the capacity of the NVRAM or the flash memory, an error message appears.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

 

OL-9775-02

22-9

 

 

 

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Cisco Systems 3750E manual Dhcp Snooping Configuration Guidelines, 22-9