Troubleshooting Network Services

There are three services in Sharing preferences that are likely to need trouble shooting if problems occur: file sharing, firewall access, and Internet Sharing. For example, file sharing is a robust and easily-configured service, but because it "just works," it can be hard to know where to start troubleshooting. This section provides some guidance to direct your troubleshooting efforts.

Troubleshooting File Sharing

If users are unable to connect to your computer, try the following:

• Verify that the appropriate file sharing service is enabled in the Services pane of Sharing preferences.

• If the appropriate service is enabled, but users are still unable to connect, there could be a networking problem such as an incorrect setting in Network preferences or a broken connection in the network.

  • Check the IP address and DNS settings in Network preferences. If an IP address starts with 169.254, it was self-assigned and therefore is accessible only to computers on the local subnet.

  • Use Network Utility to check whether or not the two computers are able to communicate using ping. For more information on trouble shooting network connectivity issues, see Lesson 8, "Networking Configuration and Troubleshooting."

  • If users are able to connect but not authenticate, verify that they are using a valid user account on the computer and that they are using the correct password.

  • Some networks and routers may block specific protocols. If the preceding strategies did not resolve the problem, check with your network administrator to see if that might be the case.

• If a user is able to connect and authenticate but is unable to access files, check to make sure that the permissions for the files the user is trying to access and all of the folders that encompass the files are set to allow access for the user. If just one encompassing folder doesn't have at least read permission for the user, the user will be blocked from accessing the files, regardless of how the files' permissions are set.

Troubleshooting the Firewall

Using the firewall protects your computer from potential exploits, and is essential in any network environment that is directly exposed to the Internet. However, it is designed to protect your computer by blocking access, and it can block network services that you want to share. If you share a service and it is not available to other computers on your network, check the firewall service.

You can specifically open ports for services and programs to which you want to allow access, such as iTunes, iPhoto, or iChat. You can also open ports for network-aware games, or even to provide special access to particular services. Keep in mind that every open port is a potential source of intrusion into your computer.

The ipfw.log file is very useful for troubleshooting firewall issues, because it can show all types of firewall usage, including denied port requests that might indicate some kind of attack.

Troubleshooting Internet Sharing

If you use the firewall, clients of your shared Internet connection may receive an IP address from your computer, but find that they cannot browse websites. Enable Personal Web Sharing in the Services pane of Sharing preferences to open a firewall port and allow computers sharing your connection to browse the web.

Internet Sharing with WEP may not allow Windows wireless computers on the network. WEP has two methods to authenticate. Windows defaults to "Open," whereas Mac OS X uses "Shared." AirPort Extreme and AirPort Express Base Stations support both modes. Windows systems may be able to use "Shared" or "Auto/Both." Check the advanced configuration options in Windows wireless software.