How to troubleshoot an ADSL connection

Caveats: This guide was developed in order to troubleshoot DSL connections for the ISP where I work. It is used for Win9x and ME customers who use Verizon for the phone company portion of their connection, and we presume you have a static IP address (ie, no DHCP). The steps listed here should help you, but your mileage will definitely vary. Everything in this guide is presented at your own risk.

I've never been able to come up with a way to effectively troubleshoot a DSL connection for a Macintosh user, because of lack of built in commands like ping, arp, and so on. Which is part of why I'm contributing this information; I hope that someone will post an equivalent guide for Mac users. If you do, I'll send 10,000 fluffly pink Energizer bunnies to your doorstep.

Not.

1. Power cycle the modem.
   • Unplug the modem, let sit for 10 seconds and then plug back in. Wait for lights to stop blinking.
   • In many cases, this will take care of the problem, so you can stop here if connectivity is restored.
2. Three solid green lights on the modem?
   • Yes, continue.
   • No, call the phone company, as the problem's in their hands.
3. Open DOS window and ping, ohhh, 63.161.154.20.
   • If ping worked, goto step 10.
   • If ping failed, continue.
4. Check for carrier light on the NIC.
   • If light is on, continue.
   • If light is off, try any/all of the following:
     • Verify you are using the correct cable from the ADSL modem to the NIC. This in some instances can be a crossover cable, so you may need to check with your ISP or phone company to make sure you've got the right one, baby.
     • Replace cable.
     • Reinstall or replace the NIC.
     • Consult vendor or geek support.
     • Call phone company for modem replacement.
5. Click the Start button, then choose Run then type winipcfg. Check IP setup for NIC (not PPP).
   • If IP is good (it matches what your ISP told you to enter when you first got the account with them), note the IP number and continue.
   • If IP is bad, fix via the TCP/IP entry under "Network" from the Control Panel.
6. Verify you have the correct gateway address for your IP address.
   • In most cases, if, for example, your IP is 192.69.69.69, your gateway address will be 192.69.69.1
7. Open a DOS window and ping your own IP address (from step 5).
   • If ping worked continue.
   • If ping failed:
     • Verify TCP/IP is installed and bound to NIC.
     • Verify NIC card settings, check for hardware conflicts.
     • Re-install NIC software (if any).
     • Re-install TCP/IP
     • Consult with Windows consultant or vendor support.
8. Ping gateway address
   • If ping failed, continue.
   • If ping worked, verify TCP/IP gateway settings.
9. Open DOS window and enter command: arp -g
   • If entry not found, call your ISP for further troubleshooting, you've done all you can do without their help.
   • If entry is found, suspect a circuit problem (one-way transmission).
     Call the phone company and have them check for bad transmission from your side of things.
10. Can you ping www.rutabaga.com (as distinct from IP address given in step 3)?
    • Yes, trouble is not in the ADSL line. Check browser config, etc.
    • No, check DNS configuration in TCP/IP.

I've omitted a couple of ISP-specific steps where they check entries in their router, but if you've gotten all the way to step 9 and haven't solved the problem, you'll need their help anyway.

The equivalent of winipcfg on the Mac is the TCP/IP control panel. This will list your IP, netmask, gateway, and default DNS server. If the IP claims to be something beginning with 169, chances are you have some problems. Don't bother trying to ping, it won't work. One solution to this is to close TCP/IP, open the System Folder, open the Preferences Folder, and trash the file "TCP/IP Preferences". Immediately reboot your Mac and reconfigure your settings, then quit and save. This works surprisingly often. While it doesn't seem to be an issue with newer versions of Open Transport, it would sometimes happen that when you crashed, your preferences file would be corrupted, leaving your Mac unable to obtain an IP address.

And if you're using the wrong kind of twisted cable between your computer and your DSL/cable modem, it will never have worked at all. That's something you'll probably have to fix.