Cisco CCNA (200-301)Network FundamentalsEasy
A new employee's laptop can successfully ping other devices on its own subnet but cannot reach any hosts on other VLANs or the internet. Which configuration item is the MOST likely cause?
- AAn expired DHCP lease on the DNS server
- BA duplicate MAC address on the local segment
- CAn incorrect subnet mask on the switch port
- DA missing or incorrect default gateway on the laptop
Show answer & explanationAnswer & explanation
Correct answer: D. A missing or incorrect default gateway on the laptop
When a host can communicate with local subnet devices but not with remote networks, the default gateway is the classic suspect because it is required to route traffic off the local segment. A subnet mask issue would typically also break local communication, and the other options are unrelated to inter-VLAN routing.
Why the other options are wrong
- A. DHCP lease expiration affects addressing, not specifically off-subnet routing.
- B. A duplicate MAC would cause local conflicts, not selective remote failure.
- C. A bad mask would usually also break local connectivity, not just remote.
Default Gateway
The default gateway is the router interface a host uses to send traffic destined for networks outside its own subnet.
- Configured on end devices via static IP or DHCP option 3
- Without it, hosts can only reach local subnet devices
- Routers/L3 switches typically serve as the default gateway
Memory trick: No gateway, no getaway from your own subnet.