Configuring a DHCP Client

Before a device can function as a DHCP client, you must enable the DHCP client function.

After an interface is enabled with the DHCP client function, the interface can obtain network parameters including the IP address from the DHCP server. If the allocated IP address and IP addresses of other interfaces are on the same network segment, the interface does not use this IP address and does not re-apply for an IP address. To allow the interface to re-apply for an IP address, run the shutdown and then the undo shutdown commands on the interface. Alternatively, run the undo ip address dhcp-alloc and then the ip address dhcp-alloc command on the interface.

Configuring attributes allows you to specify certain parameters for the DHCP client. You can configure the Option 60 field in either the system view or the interface view. The configuration in the interface view has a higher priority and overrides the configuration in the system view.

To enable a DHCP client to determine the lease length, configure an expected lease on the DHCP client. If the expected lease is longer than the global lease, the global lease takes effect.

To enable a DHCP client to detect the status of the gateway, enable the gateway detection function. A DHCP client enabled with the gateway detection function sends an ARP Request packet to detect the gateway status after obtaining an IP address. If the DHCP client receives no ARP Reply packet within the detection period, it considers the gateway address incorrect or the gateway device faulty, and then re-applies for an IP address.

To allow a DHCP client to communicate with other network devices, you need to configure a route in which the next hop address is the gateway address of the client. If the gateway address of the client is dynamically obtained from the DHCP server and the route is statically configured on the client, the static route must be manually modified when the gateway address changes. After the DHCP client is configured to dynamically obtain routing entries through DHCP, the next hop address in the static route is automatically updated when the gateway address changes, lowering maintenance costs.

A DHCP server can allocate routing entries to DHCP clients. On a device functioning as the DHCP client, you can set the priorities of routing entries allocated by the DHCP server so that the DHCP client can dynamically update its routing table.

The Option 55 field in DHCP Request messages is used to set the request option list. DHCP clients use this option to specify network configuration parameters that need to be obtained from the DHCP server. You can run the dhcp client request option-list exclude command to set a list of default options that are excluded from the Option 55 field or run the dhcp client request option-list command to set a list of other options that the Option 55 field carries besides the default options based on network requirements. The other options include option 4, 7, 17, 42, 43, 66, 67, 120, and 129.

For option meanings, see DHCP Messages in Configuration- IP Service Configuration Guide - DHCP Configuration.