Specifying the DHCP server selecting algorithm
The DHCP relay agent supports the polling and master-backup DHCP server selecting algorithms.
By default, the DHCP relay agent uses the polling algorithm. It forwards DHCP requests to all DHCP servers. The DHCP clients select the DHCP server from which the first received DHCP reply comes.
If the DHCP relay agent uses the master-backup algorithm, it forwards DHCP requests to the master DHCP server first. If the master DHCP server is not available, the relay agent forwards the subsequent DHCP requests to a backup DHCP server. If the backup DHCP server is not available, the relay agent selects the next backup DHCP server, and so on. If no backup DHCP server is available, it repeats the process starting from the master DHCP server.
The master DHCP server is determined in one of the following ways:
In a common network where multiple DHCP server addresses are specified on the DHCP relay interface, the first specified DHCP server is the master. The other DHCP servers are backup.
In a network where DHCP address pools are configured on the DHCP relay agent, the first specified DHCP server in a DHCP address pool is the master. The other DHCP servers in the DHCP address pool are backup.
The DHCP relay agent determines that a DHCP server is not available if it does not receive any response from the server within a period of time. This period of time is called the DHCP server response timeout time. The DHCP server response timeout time is configurable and the default is 30 seconds.
If the DHCP relay agent selects a backup DHCP server, it does not switch back to the master DHCP server by default. You can configure the DHCP relay agent to switch back to the master DHCP server after a delay. If the master DHCP server is available, the DHCP relay agent forwards DHCP requests to the master DHCP server. If the master DHCP server is not available, the DHCP relay agent still uses the backup DHCP server.
To specify the DHCP server selecting algorithm in interface view:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter interface view. | interface interface-type interface-number | N/A |
3. Enable the DHCP relay agent. | dhcp select relay | By default, an interface operates in the DHCP server mode when DHCP is enabled. |
4. Specify a DHCP server address. | dhcp relay server-address ip-address | By default, no DHCP server address is specified. |
5. Specify the DHCP server selecting algorithm. | dhcp relay server-address algorithm { master-backup | polling } | By default, the polling algorithm is used. The DHCP relay agent forwards DHCP requests to all DHCP servers. |
6. (Optional.) Set the DHCP server response timeout time for DHCP server switchover. | dhcp relay dhcp-server timeout time | By default, the DHCP server response timeout time is 30 seconds. |
7. (Optional.) Enable the switchback to the master DHCP server and set the delay time. | dhcp relay master-server switch-delay delay-time | By default, the DHCP relay agent does not switch back to the master DHCP server. |
To specify the DHCP server selecting algorithm in DHCP address pool view:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter interface view. | interface interface-type interface-number | N/A |
3. Enable the DHCP relay agent. | dhcp select relay | By default, an interface operates in the DHCP server mode when DHCP is enabled. |
4. Return to system view. | quit | N/A |
5. Create a DHCP address pool and enter its view. | dhcp server ip-pool pool-name | By default, no DHCP address pool exists. |
6. Specify gateway addresses for the clients matching the DHCP address pool. | gateway-list ip-address&<1-64> | By default, the DHCP address pool does not have any gateway addresses. |
7. Specify DHCP servers for the DHCP address pool. | remote-server ip-address&<1-8> | By default, the DHCP address pool does not have any DHCP server IP addresses. You can specify a maximum of eight DHCP servers for one DHCP address pool for high availability. |
8. Specify the DHCP server selecting algorithm. | dhcp relay server-address algorithm { master-backup | polling } | By default, the polling algorithm is used. The DHCP relay agent forwards DHCP requests to all DHCP servers. |
9. (Optional.) Set the DHCP server response timeout time for DHCP server switchover. | dhcp-server timeout time | By default, the DHCP server response timeout time is 30 seconds. |
10. (Optional.) Enable the switchback to the master DHCP server and set the delay time. | master-server switch-delay delay-time | By default, the DHCP relay agent does not switch back to the master DHCP server. |