Cisco CCNA (200-301)Network FundamentalsMedium
A network administrator is troubleshooting connectivity issues for a host with the IP address 192.168.1.10/25. The host can communicate with other devices within its own subnet (192.168.1.1-192.168.1.126) but cannot reach a server at 192.168.1.130. What is the most likely cause?
- AThere is a firewall blocking communication between the host and the server.
- BThe host's default gateway is incorrectly configured.
- CThe host has a duplicate IP address on the network.
- DThe server 192.168.1.130 is in a different subnet.
Show answer & explanationAnswer & explanation
Correct answer: D. The server 192.168.1.130 is in a different subnet.
The host's IP address 192.168.1.10/25 means its subnet mask is 255.255.255.128. This subnet ranges from 192.168.1.0 to 192.168.1.127. The server at 192.168.1.130 falls into the next subnet (192.168.1.128/25), making it unreachable without a router.
Why the other options are wrong
- A. While possible, a firewall issue would typically block specific ports or protocols, not necessarily all communication based on IP address range within the same /24 block.
- B. If the default gateway was incorrect, the host wouldn't be able to reach any device outside its local subnet, including other subnets, but it is reaching devices within its own subnet.
- C. A duplicate IP address would cause intermittent connectivity problems for the host itself, not specifically prevent communication with a single destination in a different subnet while allowing communication within its own.
Subnet Masking (CIDR /25)
Subnet masking divides a larger IP network into smaller, more manageable subnets, defining which portion of an IP address identifies the network and which identifies the host.
- A /25 mask corresponds to 255.255.255.128.
- A /25 mask creates two subnets from a Class C /24 network.
- Devices in different subnets require a router to communicate.
Memory trick: Same house, same conversation. Different houses need a door (router).