Cisco CCNA mock exam questions sample test – Question 301

.Which is the valid IP address range that can be assigned to hosts on the subnet that includes the address 172.16.4.6/23?

A. 172.16.2.1 – 172.16.4.254
B. 172.16.3.1 – 172.16.5.254
C. 172.16.4.1 – 172.16.5.254
D. 172.16.4.1 – 172.16.4.254

Correct Answer: C

Explanation:
172.16.4.1 – 172.16.5.254 is the valid IP address range that can be assigned to hosts on the subnet that includes the address 172.16.4.6/23.
To determine the range of addresses that can be assigned in a subnet, you must first determine the network ID and broadcast address of the subnetwork. All addresses that can be
assigned to hosts will lie between these two endpoints. The network ID can be obtained by determining the interval between subnet IDs. With a 23-bit mask, the decimal equivalent of
the mask will be 255.255.254.0. The interval between subnets can be derived by subtracting the value of the last octet of the mask from 256. In this case that operation would be 256 –
254. Therefore, the interval is 2, and it is applied in the third octet where the subnet mask ends.
The first network ID will always be the classful network you started with (in this case 172.16.0.0). Then each subnetwork ID will fall at 16-bit intervals as follows:
172.16.0.0
172.16.2.0
172.16.4.0
172.16.6.0
At 172.16.6.0 we can stop because the address that we are given in the scenario, 172.16.4.6, is in the network with a subnet ID of 172.16.4.0. Therefore, since the broadcast address
for this network will be 1 less than the next subnet ID, or 172.16.5.255, the valid range is 172.16.4.1 – 172.16.5.254.
All the other options are incorrect because these are not valid IP address ranges for this scenario.
Objective:
Network Fundamentals
Sub-Objective:
Apply troubleshooting methodologies to resolve problems
References:
Cisco > Technology Support > IP > IP Routing > Design TechNotes > IP Addressing and Subnetting for New Users > Document ID: 13788 > Understanding IP Addresses