220-1102 Question 174
Single answerInternet Protocol (IP) addressing schemeA technician is configuring a new workstation on a small office network. The router's LAN IP is 192.168.10.1/24, and other devices on the network use addresses in the 192.168.10.x range. The technician manually enters the following settings on the workstation:
IP address: 192.168.10.255 Subnet mask: 255.255.255.0 Default gateway: 192.168.10.1 DNS server: 8.8.8.8
The workstation cannot communicate with other devices on the local network. Which of the following is the MOST likely cause?
- A
The IP address is set to the broadcast address for the subnet
- B
The default gateway must be in a different subnet than the workstation
- C
The DNS server must match the router's LAN address
- D
The subnet mask should be changed to 255.255.0.0
Show answer and explanation
Correct answer: A
Explanation
In IPv4 addressing, each subnet reserves one address as the network ID and one as the broadcast address. For a /24 subnet (255.255.255.0), addresses range from x.x.x.0 to x.x.x.255, where .0 is the network address and .255 is the broadcast address. Valid host addresses are .1 through .254. In this scenario, 192.168.10.255 cannot be assigned to a workstation because it is the directed broadcast address for the 192.168.10.0/24 subnet. A best practice when manually configuring hosts is to verify that the selected IP is a valid host address, is in the correct subnet, and does not conflict with another device. This aligns with standard IPv4 subnetting behavior documented in TCP/IP networking references and vendor networking documentation.
- A. Correct.
Correct. With a subnet mask of 255.255.255.0, the network is 192.168.10.0/24. In this subnet, 192.168.10.0 is the network address and 192.168.10.255 is the broadcast address. A host cannot use the broadcast address as its assigned IP. This would prevent normal communication on the network.
- B. Incorrect.
Incorrect. In a typical IPv4 LAN configuration, the default gateway should be in the same subnet as the workstation so the host can reach it directly. Here, 192.168.10.1 is an appropriate gateway address for a 192.168.10.0/24 network.
- C. Incorrect.
Incorrect. A DNS server does not need to match the router's LAN address. It can be a public DNS server such as 8.8.8.8, an internal DNS server, or the router itself if the router provides DNS forwarding. DNS settings would not cause the host IP address itself to be invalid on the subnet.
- D. Incorrect.
Incorrect. Changing the subnet mask to 255.255.0.0 would redefine the network as 192.168.0.0/16, but that is not supported by the stated network design and would create inconsistency with the existing /24 addressing scheme. The core issue is that the selected host address is reserved as the broadcast address in the current subnet.