3Com Switch 7754, Configuration Manual

Page: 624 / 940

624 C
HAPTER
59: DHCP S
NOOPING
C
ONFIGURATION
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
82
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
DHCP Client
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