Common Networking Issues

Even though the number of dialup modem users is decreasing, they still make up a large percentage of home users and mobile users. When assisting those users, verify that the dialup account is still active. Because many ISPs provide a trial account, users frequently mistakenly try to use an expired account.

If you are using a modem, double-check the PPP settings in Network preferences. The account password may be incorrect or the phone number may no longer be valid. If using a DSL or cable modem, try restarting the modem. Sometimes a cable or DSL modem will become unresponsive and the simplest method for resetting it is to turn the modem off, wait a few seconds, and then turn it on. This may also fix a known problem where some cable modems only recognize the first MAC address that is connected to their network port.

NOTE

If you have a cable modem directly connected to your Macintosh, then add an AirPort Base Station to your home network, you would disconnect the Ethernet cable from your computer and attach it to the WAN port on the AirPort Base Station. In that situation, the cable modem may not recognize the AirPort Base Station (which has a different MAC address than your Macintosh). In this case, power cycle the cable modem, then connect it via Ethernet to the WAN port of your AirPort Base Station, configure the AirPort Base Station to authenticate with your cable ISP, and set your Macintosh to use the wireless connection.

NOTE

If your DSL or cable modem connection lights indicate a valid ISP connection, but the modem is not supplying an address to your computer, try shutting off the modem and disconnecting its power for several minutes. This clears its list of local MAC addresses and forces it to reconnect to your computer as well as to the ISP.

If there is a router between the DSL or cable modem and the computer, make sure the router has all of the correct ISP settings. A common problem with broadband connections is for a user to change the password for their ISP account and update their mail application, but forget to update the router settings. Because the password is only used while establishing a connection, the user might not immediately experience any problems. A router in this context is any device, such as an AirPort Extreme Base Station, which retains the ISP user name and password.

TIP

When troubleshooting connection issues with DSL and cable modems, and a router is connected, try validating the ISP connection with a computer connected directly to the modem. This helps eliminates any issues that could be caused by a misconfigured router. Some ISPs will not provide assistance if there is a router connected.

If you are having difficulty accessing a network service such as FTP, it might be blocked by Mac OS X's built-in firewall. If the firewall is turned on in Sharing preferences, turn it off and see if you are able to access the service in question. You will learn more about turning on and configuring the personal firewall in Lesson 10, "Providing Network Services."