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Recording a Wi-Fi Packet Trace

Record traces of Wi-Fi traffic and traffic management.

Overview

When working with Wi-Fi, your best option for recording a packet trace depends on whether you’re interested in the network traffic itself, or in the details of how the Wi-Fi network manages traffic.

Record a High-Level Packet Trace of Wi-Fi Traffic

If you’re primarily interested in the traffic going over the Wi-Fi — that is, you would like to ignore all the low-level details of Wi-Fi and treat the Wi-Fi network like an Ethernet network without all those pesky wires — use one of the following high-level approaches:

  • If possible, run the packet trace on one of the machines involved in the communication — including using RVI to record an iOS packet trace. That’s the easiest solution. See Recording a Packet Trace for instructions.

  • If your Wi-Fi access point supports bridge mode (notably, all Apple base stations do), you can bridge the Wi-Fi network on to an Ethernet network and then use standard Ethernet techniques to capture a packet trace. You won’t be able to see Wi-Fi to Wi-Fi traffic, but in many situations that’s not a problem.

  • If you enable Internet Sharing on your Mac, and have your Wi-Fi clients join the shared network, you can run your packet trace program on the Mac and see all the Wi-Fi traffic. If you target the Mac’s Wi-Fi interface, you will see all traffic, including Wi-Fi to Wi-Fi traffic. If you target the Mac’s Ethernet interface, you will only see traffic entering or leaving the Wi-Fi network.

Record Low-Level Details of Wi-Fi Traffic Management

If you are interested in the low-level details of how the Wi-Fi network manages traffic, record a low-level Wi-Fi packet trace. To do this:

  1. Choose a Mac on which to record your trace. That Mac cannot use the Wi-Fi interface for normal network traffic while recording the trace.

  2. Configure your access point to use a fixed channel. When recording a packet trace, you must specify the channel to record, and having the access point choose its channel automatically makes that harder.

  3. Either temporarily turn off the Wi-Fi password on your network or use a separate test network that has no password. If the Wi-Fi network has a password, Wi-Fi encryption makes it harder to examine the trace.

  4. Open the Wireless Diagnostics app (you can find this in /System/Library/CoreServices/Applications/).

  5. Choose Window > Sniffer.

  6. In the Sniffer window, select the channel number and width you want to record and click Start.

  7. Click Stop when you’re done.

  8. In the Finder, navigate to /var/tmp/ and look for the resulting .pcap file.

See Also

Working with Packet Traces

Troubleshooting Packet Traces

Take action to address packet tracing problems.

Submitting a Packet Trace to Apple

Learn the best way to record a packet trace when communicating with Apple.