H3C Technologies H3C SecPath F1000-E - Manual (Page 251)

5
Item Description
Unauthorized Server
Detect
Enable or disable unauthorized DHCP server detection.
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 relay agent
will record the IP address of any DHCP server that assigned an IP address to the
DHCP client and the receiving interface. The administrator can use this information
to check out DHCP unauthorized servers.
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. After the information of recorded DHCP servers is
cleared, the relay agent will re-record server information following this mechanism.
Dynamic Bindings
Refresh
Track Timer Interval
Enable or disable periodic refresh of dynamic client entries, and set the refresh
interval.
Via the DHCP relay agent, a DHCP client sends a DHCP-RELEASE unicast message
to the DHCP server to relinquish its IP address. In this case the DHCP relay agent
simply conveys the message to the DHCP server, thus it does not remove the IP
address from dynamic client entries. To solve this problem, the periodic refresh of
dynamic client entries feature is introduced.
With this feature, the DHCP relay agent uses the IP address of a client and the MAC
address of the DHCP relay agent interface to periodically send a DHCP-REQUEST
message to the DHCP server.
• If the server returns a DHCP-ACK message or does not return any message within
a specified interval, which means that the IP address is assignable now, the
DHCP relay agent will age out the client entry.
• If the server returns a DHCP-NAK message, which means the IP address is still in
use, the relay agent will not age it out.
Note that if the Auto radio button is clicked on, the refresh interval is calculated by
the relay agent according to the number of client entries.
Return to
DHCP Relay Agent Configuration Task List .
Creating a DHCP Server Group
Select Network > DHCP > DHCP Relay from the navigation tree to enter the page shown in Figure
19 . In the Server Group field, click Add to enter the page shown in Figure 20 .
Figure 20 Create a server group
Table 5 describes the DHCP server group configuration items.