3Com 2928 User Guide - Page 316
Creating a DHCP Server Group, Table 2-1, Description, Network, DHCP Relay, Server Group,
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Table 2-1 DHCP service and advanced DHCP relay agent configuration items Item Description DHCP Service Enable or disable global DHCP. 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. 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. z 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. z 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 from the navigation tree to enter the default DHCP Relay page shown in Figure 2-3. In the Server Group field, click Add to enter the page shown in Figure 2-4. Figure 2-4 Create a server group Table 2-2 describes the DHCP server group configuration items. 2-4