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Troubleshoot Network Issues

Learn to troubleshoot common macOS Big Sur network configuration issues using Network preferences and the command-line interface (CLI) in this sample chapter from macOS Support Essentials 11 - Apple Pro Training Series: Supporting and Troubleshooting macOS Big Sur.

This chapter is from the book

This lesson builds on the network topics covered in Lesson 21, “Manage Basic Network Settings,” and Lesson 22, “Manage Advanced Network Settings.” This lesson first covers general network troubleshooting and common network issues. Then, you learn how to use network troubleshooting tools and commands.

Reference 23.1 Troubleshoot General Network Issues

When you troubleshoot LAN and internet connection network issues, consider possible points of failure. Isolate the cause of the problem before you attempt generic resolutions.

To help isolate network issues, you can categorize them into three general areas:

arrow-a.jpg Local issues—These are usually related to either improperly configured network settings or disconnected network connections.

arrow-a.jpg Network issues—Many possible points of failure could be involved. Become familiar with the physical topology of your network. Start by checking the devices that provide network access closest to your Mac. Something as simple as a bad Ethernet port on a network switch can cause problems. Start your investigation using the network diagnostic utilities included with macOS.

arrow-a.jpg Service issues—These issues are related to the network device or service you are trying to access. For example, the devices providing DHCP or DNS services could be temporarily down or improperly configured. You can often determine that the problem is with the service by testing other network services. If the other network services work, you’re probably not dealing with network or local issues. Use diagnostic tools for testing service availability. Troubleshooting network services is also covered in Lesson 24, “Manage Network Services.”

Use two main tools for diagnosing network issues in macOS: Network preferences and Terminal.

Verify Network Preferences Status

One of the diagnostic tools you should check first is Network preferences. Network preferences features a dynamically updating list that shows you the current status of any network interface. If a network connection isn’t working, you first find out about it here.

Network status indicators are:

arrow-a.jpg Green—The connection is active and configured with TCP/IP settings. This doesn’t guarantee that the service is using the proper TCP/IP settings.

arrow-a.jpg Yellow—The connection is active but the TCP/IP settings aren’t properly configured. If you are experiencing problems with this service, double-check the network settings. If the settings appear sound, move on to the other diagnostic utilities.

arrow-a.jpg Red—This status usually indicates either improperly configured network settings or disconnected network interfaces. If this is an always-on interface, check for proper physical connectivity. If this is a virtual or Point-to-Point Protocol connection, double-check the settings and attempt to reconnect.

Common Network Issues

A good starting point for resolving network issues is to check for some common causes before hunting down more complex ones. This includes verifying Ethernet connectivity, Wi-Fi connectivity, DHCP services, and DNS services.

Ethernet Connectivity Issues

If you use an Ethernet connection, verify the physical connection to the Mac, and if possible, verify the entire Ethernet run back to the switch. If that’s not possible, try swapping your local Ethernet cable or use a different Ethernet port. If you use an Ethernet adapter, try a different adapter.

Verify the Ethernet status from Network preferences. Also, keep an eye out for substandard Ethernet cabling or problematic switching hardware.

You may also find that although the Ethernet switch registers a link, Network preferences still shows the link as down. This issue may be resolved by manually setting a slower speed in the advanced hardware settings of Network preferences, as covered in Lesson 22.

Wi-Fi Connectivity Issues

If you use Wi-Fi, start by verifying that you are connected to the correct SSID from the Wi-Fi status menu or Network preferences. Often, if the Mac detects a problem the Wi-Fi status menu shows an exclamation point (!) to indicate that there is a problem with the wireless network.

The Wi-Fi status menu can also serve as a diagnostic tool if you press and hold the Option key, then open the Wi-Fi status menu. This view shows connection statistics for the currently selected Wi-Fi network. Of particular note is the Tx Rate entry, which shows the current data rate for the selected Wi-Fi network. The Wi-Fi status menu is capable of other diagnostic tasks, including helping you quickly identify network issues and opening Wireless Diagnostics.

When you open Wireless Diagnostics, an assistant interface appears. Wireless Diagnostics creates and saves a diagnostic report archive about the Mac computer’s wireless and network configuration. You must authenticate as an administrator user to create the report. The compressed archive is stored in /private/var/tmp. After Wireless Diagnostics completes the report, the Finder opens the folder that contains the compressed archive.

The Wireless Diagnostics archive contains relevant files that can you use to diagnose a connection issue. If the utility can’t diagnose the problem, consult an experienced Wi-Fi administrator.

Open the Window menu to access additional advanced wireless network utilities in Wireless Diagnostics.

These utilities provide information that you can share with Wi-Fi vendors or support specialists to resolve Wi-Fi issues. For example, the Performance window provides a real-time view of the radio signal quality. With the Performance window open, you can physically move a Mac notebook computer around an area to identify wireless dead zones.

Sidecar Diagnostics is part of Wireless Diagnostics. You use it to gather information about wireless issues while you’re using your iPad as a second display for your Mac with Sidecar.

For more information, see Apple Support article HT202663, “If your Mac doesn’t connect to the Internet over Wi-Fi.”

DHCP Service Issues

If you configure your Mac to use DHCP and the DHCP server runs out of available network addresses or doesn’t provide configuration information to your Mac, your Mac might be able to communicate with other devices on the LAN even though it doesn’t have access to WAN or internet resources. This is covered in Lesson 21, “Manage Basic Network Settings.”

DNS Service Issues

Most network services require DNS services. If you have DNS service issues, verify the DNS server configuration in Network preferences. In most cases, the top listed network service interface is primary, and macOS uses it for DNS resolution. The exception is if the primary network service lacks a router configuration, in which case DNS resolution falls to the next fully configured network service interface.

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