CompTIA Server+ (SK0-005)TroubleshootingMedium
A system administrator is troubleshooting a Linux-based web server that has suddenly become unreachable from outside the local network, although it is still accessible via SSH from another server on the same subnet. Pinging the server's public IP address from an external network fails, but pinging its internal IP address from within the subnet succeeds. The server's firewall (iptables) configuration has not changed recently. Which of the following should the administrator investigate NEXT?
- AThe local firewall rules on the server.
- BThe default gateway configuration on the server.
- CThe web server software (Apache/Nginx) status.
- DThe server's internal DNS resolution.
Show answer & explanationAnswer & explanation
Correct answer: B. The default gateway configuration on the server.
The ability to access the server locally but not externally, despite no recent firewall changes, strongly suggests a routing issue. The default gateway is critical for traffic to leave the local network and reach external destinations. If it's incorrect or unreachable, external connectivity will fail while internal connectivity remains.
Why the other options are wrong
- A. The question states firewall configuration has not changed, and local SSH access works, making a local firewall rule change less likely to be the primary cause of external unreachability.
- C. Web server software status would affect web access, but the server would still be pingable and reachable via SSH if routing is correct.
- D. DNS resolution issues would affect name-based access, but pinging an IP address directly would still work if routing is correct.
Default Gateway Importance
The default gateway is a router that forwards traffic from a local network to other networks, including the internet. Its correct configuration is essential for external network connectivity.
- Allows devices to communicate outside their local subnet.
- Misconfiguration leads to external connectivity loss.
- Internal communication remains unaffected by gateway issues.
Memory trick: If you can talk to neighbors but not the world, check your gateway's unfurled.