2-23 
To do…  Use the command…  Remarks 
Enable the unauthorized DHCP server 
detecting function 
dhcp server detect 
Required 
Disabled by default. 
 
 
With the unauthorized DHCP server detection enabled, the relay agent will log all DHCP servers, 
including authorized ones, and each server is recorded only once. The administrator needs to find 
unauthorized DHCP servers from the system log information. 
 
Configuring IP Address Detecting 
To avoid IP address conflicts caused by assigning the same IP address to multiple DHCP clients 
simultaneously, you can configure a DHCP server to detect an IP address before it assigns the address 
to a DHCP client. 
The DHCP server pings the IP address to be assigned using ICMP. If the server gets a response within 
the specified period, the server will ping another IP address; otherwise, the server will ping the IP 
addresses once again until the specified number of ping packets are sent. If still no response, the server 
will assign the IP address to the requesting client (The DHCP client probes the IP address by sending 
gratuitous ARP packets). 
Follow these steps to configure IP address detecting: 
To do…  Use the command…  Remarks 
Enter system view 
system-view 
— 
Specify the number of ping 
packets 
dhcp server ping packets 
number 
Optional 
Two ping packets by default. 
Configure a timeout waiting for 
ping responses  
dhcp server ping timeout 
milliseconds 
Optional 
500 ms by default. 
 
Configuring DHCP Accounting Functions 
Introduction to DHCP Accounting 
DHCP accounting allows a DHCP server to notify the RADIUS server of the start/end of accounting 
when it assigns/releases a lease. The cooperation of DHCP server and RADIUS server implements the 
network accounting function and ensures network security at the same time. 
DHCP Accounting Fundamentals 
After you complete AAA and RADIUS configuration on a switch with the DHCP server function enabled, 
the DHCP server acts as a RADIUS client. For the authentication process of the DHCP server acting as 
a RADIUS client, refer to AAA Operation in this manual. The following describes only the accounting 
interaction between DHCP server and RADIUS server.