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DHCP static leases - First 2 digits of MAC address change

Posted: Sat Jul 14, 2018 4:36 am
by diddie17

Has anyone got any idea why the first 2 digits of the mac address keep changing on me? This happens on iPhones, Amazon Echo's, Sonos etc. and across multiple access points.

I don't think I have seen it happen on a non wireless device yet, but I have so few that it might have done and I haven't noticed.

I let the device pick up a dynamic address, and for example, if I want to do presence detection on the phone for home automation, I need to give it a static lease, so I convert the dynamic lease to a static lease, and edit the IP to where I need it to be, effectively giving it a static IP. For example on an iPhone the addess would start 88-E8-7F clearly an Apple device.

Later I'll come back and find the same device has picked up a new dynamic IP address and the mac address is identical, except that where it started with 88-E8-7F before, now if starts 8A-E8-7F. This does not seem to be a registered OUI

I see the same thing with Amazon Echo's Dot's changing from 18-74-2E to 1A-74-2E or Echo Shows from 50-DC-E7 to 52-DC-E7. It seems to consistently add 2 on to the first pair.

I used to use one of my Linux servers for DHCP and didn't have any issues that I'm aware of, but wanted to move the DHCP onto a CRS switch and am now having issues. I use static addresses heavily on wireless devices so that I know where they are for home automation purposes, so I must have them static.

Any idea what this is and how I can stop it?

Thanks in advance

Re: DHCP static leases - First 2 digits of MAC address change

Posted: Sat Jul 14, 2018 5:45 am
by chechito
i have similar problem with some rare cheap smartphones but in this case they change the latest 6 characters of MAC

in my case the OUI of this damn smartphones is 00:08:22

Re: DHCP static leases - First 2 digits of MAC address change

Posted: Sat Jul 14, 2018 8:46 pm
by diddie17
I've seen this happening now on iphones, all types of Amazon echos, various types of Sonos and a Macbook Pro laptop. I haven't seen it happening on Windows laptops yet, but given I only have 2 and 1 of them is alway hardwired and the other in not used very frequently, I suspect it will happen. I haven't seen it happening in Linux machines yet, but they are all servers and are configured with static addresses themselves.

I hate to call this a bug, but unless there's something I'm just not understanding, given how widely and often this occurs and that the device MAC address is actually being changed in the lease, although not all of the time, I'm not sure what other conclusion I can come to.

My setup is using CAPsMAN with management forwarding and VLAN's and apart from one WiFi extendedr which I guess I could turn off is all MT equipment.

Is it worth logging this with support to see if they have any ideas?