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 22-1shows the default DHCP configuration.

 

 

 

 

Table 22-1

Default DHCP Configuration

 

 

 

 

 

 

 

 

 

 

 

 

 

Feature

 

Default Setting

 

 

 

 

 

 

 

 

 

 

 

DHCP server

 

Enabled in Cisco IOS software, requires

 

 

 

 

 

 

configuration1

 

 

 

 

DHCP relay agent

Enabled2

 

 

 

 

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 information2

 

 

 

 

DHCP snooping enabled globally

Disabled

 

 

 

 

 

 

 

 

 

 

DHCP snooping information option

Enabled

 

 

 

 

 

 

 

 

 

 

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

 

 

 

 

 

 

 

 

22-8

 

 

 

 

OL-9775-02

 

 

 

 

 

 

 

Page 526
Image 526
Cisco Systems 3750E manual Configuring Dhcp Features, Dhcp Snooping and Switch Stacks, Default Dhcp Configuration, 22-8