3Com Switch 4800G 24-Port Configuration Manual page 807

Configuration
Prerequisites
Enabling Unauthorized
DHCP Server Detection
n
Configuring IP Address
Conflict Detection
Before performing this configuration, complete the following configuration on the
DHCP server:
Enable DHCP
■
Configure the DHCP address pool
■
There are unauthorized DHCP servers on networks, which reply DHCP clients with
wrong IP addresses.
With this feature enabled, upon receiving a DHCP request, the DHCP server will
record the IP address of the DHCP server which assigned an IP address to the
DHCP client and the receiving interface. The administrator can use this
information to check out any unauthorized DHCP servers.
Follow these steps to enable unauthorized DHCP server detection:
To do...
Enter system view
Enable unauthorized DHCP
server detection
With the unauthorized DHCP server detection enabled, the device puts a record
once for each DHCP server. The administrator needs to find unauthorized DHCP
servers from the log information.
To avoid IP address conflicts, the DHCP server checks whether the address to be
assigned is in use via sending ping packets.
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 conflict detection:
To do... Use the command...
Enter system view system-view
Specify the number dhcp server ping
of ping packets packets number
Configure a timeout dhcp server ping
waiting for ping timeout milliseconds
responses
Configuring the DHCP Server Security Functions
Use the command...
system-view
dhcp server detect
Remarks
-
Optional
One ping packet by default.
The value 0 indicates that no ping
operation is performed.
Optional
500 ms by default.
The value 0 indicates that no ping
operation is performed.
807
Remarks
-
Required
Disabled by default.