3com 4210 PWR 9-Port 3CR17341-91-ME User Manual

For the sake of security, the IP addresses used by online DHCP clients need to be 
tracked for the administrator to verify the corresponding relationship between the 
IP addresses the DHCP clients obtained from DHCP servers and the MAC addresses 
of the DHCP clients.

■

Switches can track DHCP clients' IP addresses through the security function of 
the DHCP relay agent operating at the network layer.

■

Switches can track DHCP clients' IP addresses through the DHCP snooping 
function at the data link layer.

Figure 87 illustrates a typical network diagram for DHCP snooping application, 
where Switch A is a Switch 4210.

Figure 87   Typical network diagram for DHCP snooping application

DHCP snooping listens the DHCP-REQUEST packets to retrieve the IP addresses the 
DHCP clients obtain from DHCP servers and the MAC addresses of the DHCP 
clients:

 

DHCP Client

 

Switch A

 

(

 

DHCP Snooping

 

)

 

DHCP Client

 

DHCP Client

 

DHCP Client

 

Switch B

 

(

 

DHCP Relay

 

)

 

Internet

 

Eth

 

1

 

/

 

0

 

/

 

2

 

Eth

 

1

 

/

 

0

 

/

 

1

 

DHCP Server