Consultant Erik Eckel offers guidance on how to approach Mac networking issues along with some specific troubleshooting tips to try first.
Network failures are among the more stressful crises enterprise Mac administrators battle. The errors are compounded by the fact they often occur at the most inopportune times and affect such critical services as the Internet, file shares and email. The next time an unexpected Mac networking failure threatens to derail your day, keep the following troubleshooting tips in mind.
Categorize the failure
Networking errors fall into one of three categories: local, network or service. Determining which type of error is occurring will help you isolate the cause and better target troubleshooting efforts.
If Web access fails on one Mac, that’s not a symptom of site-wide Internet or network failure. Check Internet access from other Macs. It’s possible the NIC is failing, the Ethernet connection is disconnected, an outdated statically-set IP address or some other issue is affecting the individual local machine.
The same is true when troubleshooting local file share access. If one system is unable to connect, a permissions issue or other problem could be to blame. But if multiple systems can no longer reach previously accessible file shares, there’s potentially a widespread network issue.
Never assume anything
Most IT professionals assume client workstations are set to use DHCP. But, as an IT consultant, I’ve learned not to assume that’s true. Often I’ve found lone workstations that refuse to connect to the network, email or the Internet. The culprit is sometimes an outdated and statically-set IP address. Be sure to confirm network settings by clicking System Preferences, choosing Network, and reviewing network settings are properly configured for the network interface in question.
Utilize the Network Utility
Mac Snow Leopard includes a Network Utility that can be employed to troubleshoot network service issues. The Network Utility, accessed from Applications/Utilities, provides a graphical interface for performing Netstat, Ping, Lookup, Traceroute, Whois, and even Finger commands. The utility also includes an integrated port scanner, which can confirm critical service ports are properly configured. Further, the port scanner enables specifying an exact port range, thereby optimizing the time required to scan suspect service ports.
DNS failures often prove perplexing, even to seasoned technology professionals. Check within System Preferences/Network to confirm that a network interface’s DNS servers are set as desired. Administrators also can use the Network Utility’s Lookup option to confirm the appropriate host name is in use.
Don’t forget DNS servers can be specified within the network interface’s Network console, as well as within the network interface’s Advanced properties. Reach the Advanced properties by clicking Advanced and clicking the DNS button, as shown below.
Forget the firewall?
Caught in the middle of a hectic day, it’s easy for an enterprise Mac administrator to forget that the Mac’s integrated firewall may be blocking needed services or intended applications. Check the Mac OS X firewall’s settings by clicking System Preferences, Security, and selecting Firewall. If the Firewall is enabled, consider disabling it just long enough to determine whether the firewall is blocking necessary or desired network traffic.
Firewall exceptions are easy to create. Click the Advanced button and manually enable specific applications by clicking the + icon, selecting the appropriate application(s), and clicking Add, then OK.
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