Primary and secondary subnets configuration example

As shown in Figure 24, the DHCP server (Router A) assigns IP addresses to DHCP clients in the LAN.

Configure two subnets in the address pool on the DHCP server: 10.1.1.0/24 as the primary subnet and 10.1.2.0/24 as the secondary subnet. The DHCP server selects an IP address from the secondary subnet when the primary subnet has no assignable addresses.

Router A assigns the following parameters:

• The default gateway 10.1.1.254/24 to clients on subnet 10.1.1.0/24.

• The default gateway 10.1.2.254/24 to clients on subnet 10.1.2.0/24.

# Enable DHCP.

<RouterA> system-view
[RouterA] dhcp enable

# Configure the primary and secondary IP addresses of interface GigabitEthernet1/0/1, and enable the DHCP server on GigabitEthernet 1/0/1.

[RouterA] interface gigabitethernet 1/0/1
[RouterA-GigabitEthernet1/0/1] ip address 10.1.1.1 24
[RouterA-GigabitEthernet1/0/1] ip address 10.1.2.1 24 sub
[RouterA-GigabitEthernet1/0/1] dhcp select server
[RouterA-GigabitEthernet1/0/1] quit

# Create DHCP address pool aa.

[RouterA] dhcp server ip-pool aa

# Specify the primary subnet and the gateway for dynamic allocation.

[RouterA-dhcp-pool-aa] network 10.1.1.0 mask 255.255.255.0
[RouterA-dhcp-pool-aa] gateway-list 10.1.1.254

# Specify the secondary subnet and the gateway for dynamic allocation.

[RouterA-dhcp-pool-aa] network 10.1.2.0 mask 255.255.255.0 secondary
[RouterA-dhcp-pool-aa-secondary] gateway-list 10.1.2.254
[RouterA-dhcp-pool-aa-secondary] quit
[RouterA-dhcp-pool-aa] quit

# Verify that the DHCP server assigns clients IP addresses and gateway address from the secondary subnet when no assignable address is available from the primary subnet. (Details not shown.)

# On the DHCP server, display IP addresses assigned to the clients. The following is part of the command output.

[RouterA] display dhcp server ip-in-use
IP address       Client identifier/    Lease expiration      Type
                 Hardware address
10.1.1.2         0031-3865-392e-6262-  Jan 14 22:25:03 2015  Auto(C)
                 3363-2e30-3230-352d-
                 4745-302f-30
10.1.2.2         3030-3030-2e30-3030-  Jan 14 22:25:03 2015  Auto(C)
                 662e-3030-3033-2d45-
                 7568-6572-1e