Does Big Sur randomize MAC addresses??

[Monotremata]

Having a weird issue on my network now (Frontier Fios if that matters), and the only change to the network has been me updating my Mac mini 2018 to Big Sur last week. Im hoping its Big Sur, otherwise I got something serious going on here. Maybe Frontier flipped a switch or something this weekend?

I have a couple of ports forwarded in my router at home and noticed my Mac wasn't communicating properly last night. I logged into the router and noticed my Mac (along with a bunch of other devices, mainly everyones iPhones and iPads) all had two entries in the DHCP table. Each one had an IP address with its actual hardware MAC listed, and then about 2 minutes after signing in, another one will pop up with a new address, but the MAC now starts with 8A:41:FC and the last three numbers are from the actual MAC address. Looking in the network prefs, my Mac still shows its actual hardware address, but now my IP is the one that's pointing to the 8A:41:FC version in the router. I cant set port forwarding, I cant reserve DHCP addresses nothing, because if I set it to one, occasionally it will bounce back and forth between the addresses and none of my services point to the right computer. I cant even make a DHCP entry for our canon printer because even it was doing the same thing. The odd part is, its not just the Apple stuff, there are quite a few devices that are doing this (my Xbox and Switch did it as well). At first I was thinking I had some internet sharing on by default and my Mac was being the gateway but nope, this stuff is all off, no sharing of anything whatsoever.

The ONLY change that's been made here has been me updating to Big Sur, but I didn't notice this right away last week so it may not have popped up until this past weekend, Im not exactly sure. Last night while troubleshooting, I shut the Mac mini's wifi off, rebooted the router, and then signed into it from my iPhone (running iOS 13).. Everything was fine until the minute I turned the Mini on, and those new duplicate reservations started popping up. Even reset the router to defaults and started from scratch, those fake addresses were there from the minute stuff started connecting.. Frontier just upgraded this router like 2-3 weeks ago (they bumped us up to gigabit) and it was perfectly fine when I initially setup port forwarding the day the tech was here. Our kid got one of those Airi extenders, but that's been in place since before we were even upgraded to the gigabit connection and its never done anything other than let him connect in his room.

 

[Superhai]

As far as I know only iOS does the random MAC yet, not Big Sur. And for my network the random MAC seem to not cause any issue. I did have some higher issues with the DHCP server, when I first installed Big Sur on my MBP on my Unifi network. But it sorted itself after a short while. There was an high number of requests which failed. There may be some bug or new feature in macOS, which causes problems for routers. And maybe for a cheap router it may be overwhelmed and stop responding. Do the same problem occur if you give your Mac a static IP on your network?

 

[Monotremata]

I think its some new 'feature' in our router that someone turned on last weekend, combined with the Airi hotspot extender thing. Frontier has this 'total control' thing on their routers that combines the 2.4G and 5G bands and automatically bounces you where you need to go without having two different SSIDs.. Apparently the Airport card in this Mac isn't strong enough to connect to the 5G network in the next room, so what its doing is jumping onto the Airi and that is handing it over to the 5G WLAN (it connected just fine before we got our "upgrade"). I noticed while playing in the Airi that its BSSID is 88:41:FC so Im assuming its using some weird pseudo addressing thing for the devices its handing over to the 5G network.

I THINK the reason I was seeing two DHCP reservations is because when it first connects, my Mac would jump right on the 2.4Ghz band (this is when it would show its actual MAC), and a minute or so later, it jumps on the Airi and that's when the second IP reservation shows up. When I initially setup port forwarding, none of this was an issue but then again, I didn't pay attention to the MAC, I just made the reservation based on the computers name in the table.