CCNA Exam Prep Question of the Week

You work for Global Knowing Ledges. You are tasked to configure the addressing for the perimeter router. Use the network 172.16.0.0 255.255.0.0. After subnetting 4 bits, which of the following will configure the FastEthernet interface with the first host IP address of the fifth subnet and the Serial interface with the first host IP address of the sixth subnet. Use the zero subnet.

1. “router # configure terminal
router (config)# interface fa 0/0
router (config-if)# ip address 172.16.5.1 255.255.255.0
router (config-if)#interface serial 1/0
router (config-if)#ip address 172.16.6.1 255.255.255.0”

2. “router # configure terminal
router (config)# interface fa 0/0
router (config-if)# ip address 172.16.64.1 255.255.248.0
router (config-if)#interface serial 0/0
router (config-if)#ip address 172.16.80.1 255.255.248.0”

3. “router # configure terminal
router (config)# interface fa 0/1
router (config-if)# ip address 172.16.64.1 255.255.240.0
router (config-if)#interface serial 0/0
router (config-if)#ip address 172.16.80.1 255.255.240.0”

4. “router # configure terminal
router (config)# interface fa 0/1
router (config-if)# ip address 172.16.5.1 255.255.240.0
router (config-if)#interface serial 0/0
router (config-if)#ip address 172.16.6.1 255.255.240.0”

5. “router # configure terminal
router (config)# interface fa 0/1
router (config-if)# ip address 172.16.80.1 255.255.240.0
router (config-if)#interface serial 0/0
router (config-if)#ip address 172.16.96.1 255.255.240.0”
The correct answer is 3.

This class B address with 4 subnet bits will have a mask of /20 or 255.255.240.0. The 5th subnet has subnet bits 0100 in the 3rd octet; the 6th subnet has subnet bits 0101 in the 3rd octet. The first host has host bits 0000 00000001 in the 3rd and 4th octet. When concatenated the bits for the FastEthernet are 01000000 00000001 or 64.1 decimal; for the Serial interface the bits are 01010000 00000001 or 80.1 decimal.

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