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Figure 42 Network diagram
Procedure
1.
Assign IP addresses to interfaces on the routers. (Details not shown.)
2.
Configure Router B and Router C as DHCP servers. (Details not shown.)
3.
Configure the DHCP relay agent on Router A:
# Enable DHCP.
<RouterA> system-view
[RouterA] dhcp enable
# Enable the DHCP relay agent on GigabitEthernet 1/0/1.
[RouterA] interface gigabitethernet 1/0/1
[RouterA-GigabitEthernet1/0/1] dhcp select relay
# Specify the IP addresses of the DHCP servers.
[RouterA-GigabitEthernet1/0/1] dhcp relay server-address 1.1.1.1
[RouterA-GigabitEthernet1/0/1] dhcp relay server-address 2.2.2.2
# Specify the DHCP server selecting algorithm as master-backup.
[RouterA-GigabitEthernet1/0/1] 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.
[RouterA-GigabitEthernet1/0/1] dhcp relay master-server switch-delay 3
[RouterA-GigabitEthernet1/0/1] quit
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.)
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Troubleshooting
