How does the OSI model help in troubleshooting a "No Internet" connection?

All answers to this question.

"Bottom-up" is for connectivity issues; "Top-down" is better when the hardware is fine but the specific application is failing.

   Answered 2024-11-06 by Karen Phillips

• Great distinction, Karen. If they can get to Google but not the company portal, you start at Layer 7 and work your way down.

     Commented 2024-11-07 by Emily Rodriguez

At what point in the troubleshooting process should we check for DNS issues? Is that considered a Layer 3 or Layer 7 problem?

   Answered 2024-11-07 by James Wilson

• James, DNS is technically an Application layer protocol (Layer 7). However, if your IP settings (Layer 3) are wrong, DNS won't work anyway. Always verify you have a valid IP and can ping a public address like 8.8.8.8 first. If you can ping the IP but not the URL, then you know it's a Layer 7 DNS issue.

     Commented 2024-11-09 by Steven Harris

Start at Layer 1: Is the link light on? If not, it's the cable or the port. Move to Layer 2: Can you see the MAC address in the switch table? Then Layer 3: Can you 'ping' the gateway? I managed a global service desk in 2024, and 70% of our "complex" outages were solved by just going back to basics. We found a "Layer 3" issue where a duplicate IP was causing a routing loop. By following the OSI steps, my team didn't waste time checking software settings at Layer 7 when the problem was actually a misconfigured router at Layer 3.

   Answered 2024-12-20 by Dorothy Adams