iMac Wont Connect to Router by WIFI

[Lesleybd]

A couple of months ago I changed to Fibre 150. All my devices are working perfectly except for my iMac. I usually connect it via ethernet but recently tried to connect by wifi. It won't connect. I spent an hour on the phone yesterday with Apple Support and it looks as if the issue is the router. I can connect via a hotspot using my phone and I can connect to a nearby  unsecured network. Mac diagnostics say this: 

Self-Assigned IP Address

Your Mac has a self-assigned IP address because it can’t locate a DHCP server.

A self-assigned IP address is provided by the Mac itself when it cannot find a DHCP server. Your Mac will require a valid IP address before you will be able to connect to the internet.

Contact your Internet Service Provider for further assistance.

Has anyone had a similar issue? I dread phoning support because I know they'll just blame my Mac.

[KeithFrench]

You must set it to the channel that your router is using, or there won't be anything in the trace. I think that the iMac will tell you the channel as well; you'll have to Google that.

It saves the trace in a .pcap file, which is what I want. The problem with attaching it to your thread is that it can be downloaded by anyone in the world. You cannot attach it to a PM, so I came up with this method. It works well for Windows PCs, I have no idea about Apple at all. In Windows, you use an application called 7-Zip, which will zip it up & allow a password to be used to later unzip it. Then you attach the zip file (it is not the compression, but the security that is important) to this thread & you send me the password in a PM.

If you can't do that, can you share the file from Dropbox, Google Drive or similar? If you can, then PM me the link to the shared file.

[Lesleybd]

Hi, Keith.

I managed to use the Sniffer then find where it had saved the trace to. I opened the trace in WireShark then compressed and saved it. There was no option to save it in the format you suggested or to add a password (as far as I could see). Do you want me to attach it here anyway? One confusing thing. In the Sniffer there was a long list of channels to choose from and I didn't know what to choose.  So I chose Channel 2 at random.

[KeithFrench]

Hi @Lesleybd 

Another Google search says that you can't use Wireshark to take the trace on an iMac, only to view it. You have to take the trace via an inbuilt tool first. If you can try taking the trace like this & as before, start the trace with the WiFi disconnected, try connecting & when it fails, stop the trace, save it & send it to me. This is what I found directly from Google:-

To take a Wireshark trace of a Wi-Fi interface on an iMac, you must first use the built-in macOS Wireless Diagnostics app to perform the capture, as Wireshark cannot do it directly on macOS. Open Wireless Diagnostics (accessible via Option-click on the Wi-Fi icon), select the "Sniffer" from the Window menu, and then start the capture on the correct Wi-Fi channel and width. The .pcap file generated will be in /var/tmp, and you can open this file with Wireshark to analyze the 802.11 packet data. 

Step-by-step guide:

1. 1. Open Wireless Diagnostics:

   Press and hold the Option key while clicking the Wi-Fi icon in your menu bar, then select "Open Wireless Diagnostics". 
2. 2. Open the Sniffer:

   In the Wireless Diagnostics window, go to the Window menu and select Sniffer. 
3. 3. Configure the Sniffer:

   Choose the correct Wi-Fi channel and width that your access point is using from the dropdown menus in the Sniffer window. 
4. 4. Start the Capture:

   Click the Start button to begin capturing packets. You may need to enter your Mac's administrator password to authorize the capture. 
5. 5. Stop the Capture:

   When you are finished capturing the Wi-Fi traffic, click Stop. 
6. 6. Locate the Capture File:

   The captured packet trace will be saved as a .pcap file in the /var/tmp/ directory. 
7. 7. Open the File in Wireshark:

   Launch Wireshark, go to File > Open, and navigate to /var/tmp/ to select and open your captured packet file. You can then analyze the detailed 802.11 frame data within Wireshark. 

[KeithFrench]

You do not want to apply any filters at all. So long as en1 is the WiFi interface you are trying to use & you set Wireshark to capture on that interface, it should be fine. Save the trace, zip it up ideally with 7 Zip & set a password on it. Attach the zip to your thread & PM me the password. Then I will take a look at it.

[Lesleybd]

Thank you, Keith.

I have installed Wireshark and the ChmodBPF tool. Can you tell me what filter I should be choosing to collect packets? When I select Wi-Fi: en1. It says its collecting packets when I try to join my wireless network but nothing is actually collected. Im a bit out of my depth here. 🙂

My router is a TalkTalk WiFi Hub/ Fast 5464-2.T4

[ferguson]

Just to add, for Apple silicon read ARM. 

[KeithFrench]

Hi @Lesleybd 

I have been looking into the Apple chip & Wireshark & found this. It is supposed to be fully compatible:-

https://isapplesiliconready.com/en/app/Wireshark 

I also found this via Google:-

To install Wireshark on an Apple Silicon (M1/M2/M3) Mac, visit the official Wireshark website and download the macOS disk image (.dmg) file. The installer is a universal binary designed to run natively on Apple Silicon Macs. After downloading, open the disk image, drag the Wireshark application to your /Applications folder, and then install the "ChmodBPF" launch daemon for packet capturing to function correctly. 

Installation Steps

1. 1. Download:

   Go to the Wireshark download page and download the official macOS package. The current macOS installer is a universal binary that runs on both Intel and Apple Silicon Macs. 
2. 2. Open:

   Locate the downloaded disk image (.dmg) file in your Downloads folder and open it. 
3. 3. Install:

   Drag the Wireshark application from the disk image to your /Applications folder. 
4. 4. Launch:

   Open the Wireshark application from your Applications folder. 
5. 5. Install ChmodBPF:

   For packet capturing to work, you must also install the "ChmodBPF" launch daemon. This is usually an automated process during the Wireshark installation on macOS. 
6. 6. Enter Password:

   The installation process will likely prompt you for your administrator password to complete the installation and set up the necessary permissions. 

Important Considerations

• Official Source:

  Always download software from the official source to ensure you get the latest, legitimate version. 
• Apple Silicon (Universal Binary):

  The macOS package is a universal binary, meaning it's designed to run natively on Macs with Apple Silicon chips, like your M1, M2, or M3. 
• Permissions:

  You'll need administrator privileges on your Mac to install Wireshark and its supporting components. 
• Packet Capturing:

  The ChmodBPF tool is crucial for Wireshark to capture network packets, so make sure its installation is completed successfully during the setup. 

[KeithFrench]

No problem, whether or not there is a Wireshark version for that chip, perhaps one of the other two will work, I have no idea. Unfortunately, I do not have an iMAC to test it with.

Do not worry about interpreting the results; I will do that for you. I will send a PM to you that contains a link to a guide of mine on Wi-Fi interference. 

[Lesleybd]

Hi, Keith. I had a bit of a hectic day yesterday and didn't have time to run Wireshark. I noticed when I went to download it I get the choice of the version for Intel Macs or Arm Macs. My iMac has the newer Apple chip and there isn't an option for that. I would appreciate a copy of your guide. Tank you.

[amahle-TT]

@Lesleybd hi there, please do let us know how it goes. @KeithFrench thank you!

[KeithFrench]

I can supply a guide if you want it.

[Lesleybd]

Thank you. I will install Wireshark and get back to you.

[KeithFrench]

Which make & model of router do you have?

There is a problem with the DHCP process between the Mac & the router, I am not blaming either. The best way to diagnose this, is to install Wireshark (free software) on your Mac. Then:-

1. Start a trace running in it before you attempt to connect to the router
2. Then try to connect to the router
3. When it fails, stop the trace & save it.
4. Send it to me for analysis.

I can provide full details on how to install & use Wireshark if you want.

The information below is provided by TalkTalk. For confirmation, please contact @Lorrainef, the manager of the TalkTalk support staff on this forum.

KeithFrench is one of our valued Community Stars and can help with a range of issues related to wireless and networking. At times, he may ask you to send him test results via a Private Message to help analyse/diagnose an issue. Although Keith does not work for TalkTalk, he very kindly shares his time and knowledge to help others.

If you need further help or if we need to take any details such as personal information about your account, like phone numbers, account numbers, etc, one of the TalkTalk team will jump in and help out.