3Com Switch 7750 Configuration Guide

624 CHAPTER 59: DHCP SNOOPING CONFIGURATION

Figure 157 Typical network diagram for DHCP snooping application

Figure 158 illustrates the interaction between a DHCP client and a DHCP server.

Figure 158 Interaction between a DHCP client and a DHCP server

DHCP snooping listens to the following two types of packets to retrieve the IP

addresses the DHCP clients obtain from DHCP servers and the MAC addresses of

the DHCP clients:

■ DHCP-ACK packet

■ DHCP-REQUEST packet

Introduction to

DHCP-Snooping Option

Introduction to Option 82

For details about Option 82, refer to “Option 82 Support” on page 612.

Padding content and frame format of Option 82

There is no specification for what should be padded in Option 82. Manufacturers

can pad it as required. By default, the sub-options of Option 82 for the Switch

7750 (enabled with DHCP snooping) are padded as follows:

DHCP Client

Switch A

(DHCP Snooping)

DHCP Client

Switch B

(DHCP Relay)

Internet

DHCP Server

DHCP-DISCOVER

DHCP-OFFER

DHCP-REQUEST

DHCP-ACK

DHCP client DHCP server

DHCP-REQUEST(renew)

DHCP-ACK