CompTIA A+ Core 1 (220-1201)NetworkingHard
A user reports that after configuring port forwarding on a SOHO router to allow external access to an internal web server, remote connections still fail while local connections work fine. The router shows the forwarding rule is correctly pointing to the server's internal IP and port 80. What should the technician check next?
- AWhether the wireless SSID is broadcasting
- BWhether the ISP is blocking inbound port 80 traffic
- CWhether the internal DNS server is running
- DWhether the DHCP scope has available leases
Show answer & explanationAnswer & explanation
Correct answer: B. Whether the ISP is blocking inbound port 80 traffic
Many ISPs block common inbound ports like 80 and 25 on residential connections to prevent users from hosting servers, which would explain why port forwarding is configured correctly but external access still fails. Local connections work because they don't traverse the ISP's filtering.
Why the other options are wrong
- A. SSID broadcasting affects local wireless discovery, not external port forwarding.
- C. DNS issues would affect name resolution, not the ability to reach a correctly forwarded port by IP.
- D. DHCP lease exhaustion would prevent internal devices from getting addresses, not affect external access.
ISP Port Blocking
Some ISPs block inbound traffic on common server ports (like 80, 25) on residential/consumer accounts to discourage self-hosting, which can cause port forwarding to appear broken even when configured correctly.
- Port forwarding maps external port to internal IP:port on router
- ISP-level blocks occur upstream of the router and can't be fixed locally
- Testing with a port-checking tool from outside the network helps confirm ISP blocking
Memory trick: Correct config but no access outside? Blame the ISP's gate first.