Downgrading AirPort Extreme to 7.6.1

I made a mistake last Thursday evening: upgraded my AirPort Extreme base station’s firmware to 7.6.3. Until Sunday afternoon WAN routing stopped three times (for which I first blamed our ISP), but when WiFi is also stopped last afternoon I decided to go back to the very well behaving 7.6.1.

But, to rephrase what Mr. Scott said: downgrading is easy, finding the file – that’s hard. Apple’s respective firmware page is an insult: it contains no link to the firmware update itself. Google turned up nothing, so I decided to go after a solution myself.

Note that I’m still using AirPort Utility 5.6. I consider 6.0 a huge step backward.

AirPort Utility stores the firmware files under the ~/Library/Application Support/Apple/AirPort/Firmware folder. You have a numbered subfolder for each model. My 4th generation AirPort Extreme’s number is 114. Here I found just one file: 7.6.3.basebinary.

So I knew that I had to look for 7.6.1.basebinary and put it into that folder. I also found a file named version.xml under the Firmware folder. Opening it quickly revealed that it contains actual download links for firmware images under the firmwareUpdates key (it’s actually an array of dictionaries, with each element corresponding to a firmware file). To find your file look for a dictionary containing your product number under the productID key, 7.6.1 under the version key, and you’ll get the download link in the location key, as you can see below:

<dict>
    <key>location</key>
    <string>http://apsu.apple.com/data/114/041-3395.20120130.Ka1Br/
        7.6.1.basebinary</string>
    <key>productID</key>
    <string>114</string>
    <key>version</key>
    <string>7.6.1</string>
    <key>sourceVersion</key>
    <string>76100.4</string>
    <key>sizeInBytes</key>
    <integer>6364116</integer>
</dict>

Also note that I had to download the firmware directly attaching the ADSL modem to my Mac, as at the end routing was so hectic that I was not able to do it via the AirPort Extreme. Having downloaded the file the actual downgrade procedure was seamless: put the file in the aforementioned folder and choose “Upload Firmware…” from the “Base Station” menu in AirPort Utility 5.6.

I also noticed a strange thing: while on 7.6.3 the Upload Firmware dialog only allowed me to upload 7.6.3 and nothing else. Now that I’m back on 7.6.1, it allows me to choose between 7.5.2, 7.6, 7.6.1 and 7.6.3.

All is well since then.

Update 8/14/2013

Just installed 7.6.4. I’ll report after a week or so how it works.