Configure active and standby DHCP servers for S series switches


The active and standby DHCP servers can be configured on S series switches (except the S1700). To improve network reliability, you can deploy two DHCP servers, one as the master server and the other as the backup server. VRRP can be configured on the two servers. When the master server is faulty, the backup server dynamically assigns IP addresses to hosts, ensuring that host services are not interrupted.

In normal cases, the master device dynamically allocates IP address to clients. When the master device is faulty, VRRP triggers a master/backup switchover in which the backup device takes over the role of the master device and dynamically allocates IP addresses to clients.

Real-time data backup cannot be implemented between master and backup devices in the VRRP group. To prevent IP address conflict after the master/backup switchover, the IP address ranges configured on master and backup devices must be different. In this way, after the master/backup switchover, the backup device assigns network configuration parameters such as IP addresses to newly online DHCP clients. Some clients have obtained IP addresses from the master device, and send Request messages to the DHCP server to request lease renewal. Because their IP addresses do not exist on the backup device, the backup device returns DHCP NAK messages so that these clients will apply for new IP addresses.

When the original master device recovers, users can decide whether to switch service traffic back to the master device depending on the actual requirements.

When configuring the DHCP server in the VRRP network, pay attention to the following items:

- To implement this function, the system version is required to be upgraded to V100R006C00SPC800 or a later version.

- In spite of different IP address ranges of master and backup devices in the VRRP group, both of IP address pools use the virtual IP address as the gateway.

- In the two address pool views, run the exclude command to exclude real IP addresses of master and backup devices in the VRRP group to prevent address conflict.

- Only a half of planned IP address segments can be used simultaneously. Therefore, the same number of extra IP addresses need to be planned, consuming large amounts of IP address resources.

For configuration details about the master and backup DHCP servers, click S系列交换机:VRRP组网下同网段内配置基于全局地址池的DHCP服务器示�?.

Other related questions:
Work mode of active and standby MPUs on S series switches
MPU is a mandatory card for switches. Each switch must be configured with one or two MPUs. When only one MPU is configured for a switch, the MPU can be installed in either MPU slot of the switch. When two MPUs are configured, they work in hot standby mode to improve system reliability. The two MPUs monitor each other. If the active MPU fails, the standby MPU changes to active state to ensure non-stop services.

Method to configure DHCP server on S series switches
For S series switches excluding the S1700, the switch can function as the DHCP server to assign IP addresses to DHCP clients. Two configuration modes are available: - Interface address pool: This mode is simple. It only applies to scenario where the DHCP server and DHCP client are located on the same network segment, that is, there is no need to deploy the DHCP relay agent. - Global address pool: It applies to the scenario where the DHCP server and DHCP client are located on different segments, that is, the DHCP relay agent needs to be deployed. It also applies to the scenario where the DHCP server and DHCP client are located on the same network segment and IP addresses to be assigned to clients on multiple interfaces.

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