Example: Configuring DHCP server selection
Network configuration
As shown in Figure 28, the DHCP client and the DHCP servers are in different subnets. DHCP server 1 and DHCP server 2 both have a DHCP address pool that contains IP addresses in subnet 22.22.22.0/24, but neither has DHCP enabled.
Configure the DHCP relay agent for the DHCP client to obtain an IP address in subnet 22.22.22.0/24 and other configuration parameters from a DHCP server. The DHCP relay agent is connected to the DHCP client through VLAN-interface 2, to DHCP server 1 through VLAN-interface 3, and to DHCP server 2 through VLAN-interface 4.
Figure 28: Network diagram
Procedure
IMPORTANT: By default, interfaces on the device are disabled (in ADM or Administratively Down state). To have an interface operate, you must use the undo shutdown command to enable that interface. | ||
Assign IP addresses to interfaces on the switches. (Details not shown.)
Configure Switch B and Switch C as DHCP servers. (Details not shown.)
Configure the DHCP relay agent on Switch A:
# Enable DHCP.
<SwitchA> system-view [SwitchA] dhcp enable
# Enable the DHCP relay agent on VLAN-interface 2.
[SwitchA] interface vlan-interface 2 [SwitchA-Vlan-interface2] dhcp select relay
# Specify the IP addresses of the DHCP servers.
[SwitchA-Vlan-interface2] dhcp relay server-address 1.1.1.1 [SwitchA-Vlan-interface2] dhcp relay server-address 2.2.2.2
# Specify the DHCP server selecting algorithm as master-backup.
[SwitchA-Vlan-interface2] dhcp relay server-address algorithm master-backup
# Configure the DHCP relay agent to switch back to the master DHCP server 3 minutes after it switches to the backup DHCP server.
[SwitchA-Vlan-interface2] dhcp relay master-server switch-delay 3
Verifying the configuration
# Verify that the DHCP client cannot obtain an IP address and that the following log is output in about 30 seconds.
DHCPR/3/DHCPR_SERVERCHANGE: -MDC=1; Switched to the server at 2.2.2.2 because the current server did not respond.
# Enable DHCP on the DHCP server at 1.1.1.1. (Details not shown.)
# Verify that the DHCP client cannot obtain an IP address and that the following log is output in about 3 minutes.
DHCPR/3/DHCPR_SWITCHMASTER: -MDC=1; Switched to the master DHCP server at 1.1.1.1.
# Verify that the DHCP client obtains an IP address. (Details not shown.)