220-1102 Question 176
Single answerSubnet maskA technician is troubleshooting a Windows workstation that cannot access a file server after a small office moved several devices to a new subnet. The workstation has IP address 192.168.10.45, default gateway 192.168.10.1, and subnet mask 255.255.255.0. The file server has IP address 192.168.11.20 and is known to be reachable from other systems. The user can ping 192.168.10.1 successfully but cannot ping 192.168.11.20. Which change is most likely to allow the workstation to communicate with the file server without changing its IP address?
- A
Change the workstation subnet mask to 255.255.254.0
- B
Change the workstation default gateway to 192.168.11.1
- C
Change the workstation IP address to 192.168.11.45 and keep the same subnet mask
- D
Change the file server subnet mask to 255.255.255.255
Show answer and explanation
Correct answer: A
Explanation
The key issue is whether 192.168.10.45 and 192.168.11.20 are considered part of the same network. With a mask of 255.255.255.0 (/24), they are on different subnets: 192.168.10.0/24 and 192.168.11.0/24. If the office intended these addresses to coexist on one larger subnet, the workstation needs a mask of 255.255.254.0 (/23), which combines those two adjacent ranges into one network. This is consistent with standard IPv4 subnetting practices documented in networking references and vendor documentation such as Microsoft TCP/IP configuration guidance and Cisco subnetting materials. In troubleshooting, verify the IP address, subnet mask, and default gateway together, because an incorrect mask commonly causes hosts to misidentify whether traffic is local or must be sent to a router.
- A. Correct.
Correct. A subnet mask of 255.255.254.0 (/23) makes the range 192.168.10.0 through 192.168.11.255 part of the same logical subnet. That allows a host at 192.168.10.45 and a server at 192.168.11.20 to be treated as local neighbors without changing the workstation's IP address. This matches the requirement and is a realistic fix when a network is expanded to include two adjacent Class C-style ranges in one subnet.
- B. Incorrect.
Incorrect. Changing the default gateway to 192.168.11.1 would place the gateway outside the workstation's currently defined local subnet when using 255.255.255.0. In addition, the user can already reach the current gateway at 192.168.10.1, so the immediate issue is not basic gateway connectivity. This option reflects the common misconception that any communication problem between subnets is solved by changing the gateway, even when the subnet mask is the actual mismatch.
- C. Incorrect.
Incorrect. This could potentially place the workstation in the same /24 network as the file server, but the question specifically asks for a solution without changing the workstation's IP address. It is therefore not the best answer. This distractor targets the idea that renumbering a host is the first fix, even when adjusting the mask is the cleaner and requested solution.
- D. Incorrect.
Incorrect. A subnet mask of 255.255.255.255 is a /32 mask, which identifies only a single host address and is not appropriate for normal LAN communication between hosts. Applying this to the file server would not solve the problem and would likely break connectivity further. This option represents confusion between host routes and standard subnetting on endpoint devices.