How to Verify DHCP Relay Agent Address on Cisco IOS Router

D.

The command used to verify the DHCP relay agent address that has been set up on a Cisco IOS router is "show ip interface brief" (option A).

Explanation:

The DHCP relay agent is used to forward DHCP requests from clients in one IP subnet to a DHCP server in another IP subnet. This is commonly used in environments where the DHCP server is not located on the same subnet as the clients.

To set up a DHCP relay agent on a Cisco IOS router, you would use the "ip helper-address" command on the interface that is connected to the client subnet. For example, if the DHCP server is located on the 192.168.1.0/24 subnet and the router interface connected to the client subnet is FastEthernet0/0, the configuration would look like this:

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interface FastEthernet0/0  ip address 10.0.0.1 255.255.255.0  ip helper-address 192.168.1.10 

In this example, the IP address of the DHCP server is 192.168.1.10, and the IP address of the router interface connected to the clients is 10.0.0.1.

To verify that the DHCP relay agent has been set up correctly, you can use the "show ip interface brief" command. This command displays a summary of the interfaces configured on the router, including their IP addresses, subnet masks, and status. If the "ip helper-address" command has been configured on an interface, the output of the "show ip interface brief" command will include a line that shows the IP address of the DHCP server that is being relayed to, as shown below:

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Router# show ip interface brief Interface                  IP-Address      OK? Method Status                Protocol FastEthernet0/0            10.0.0.1        YES manual up                    up       FastEthernet0/1            192.168.1.1     YES manual up                    up       Serial0/0/0                unassigned      YES unset  down                  down     Serial0/0/1                unassigned      YES unset  down                  down     Vlan1                      unassigned      YES unset  administratively down down     NVI0                       unassigned      NO  unset  up                    up       FastEthernet1/0/1          unassigned      YES unset  down                  down     FastEthernet1/0/2          unassigned      YES unset  down                  down     Router#  

In this example, the "ip helper-address" command has been configured on the FastEthernet0/0 interface, and the output shows the IP address of the DHCP server that is being relayed to (192.168.1.10).

Therefore, the correct answer to the question is option A, "show ip interface brief".