Hello!
In his Mikrotik using DHCP-server, IP address lease made by the MAC.
Binding MAC and IP is use to assign some other rules for the connection.
Everything was good, but lately there have been a devices dynamic MAC address (particularly Android).
Each time you connect only the first three bytes of the MAC addresses do not change (for example 00: 08: 22: xx: xx: xx).
As in this example make configure DHCP-server?
PS I apologize if I repeat an existing topic. I do not know English. I use a translator from Google.
To have dynamic mac address is not common. It looks like there is running some program on the android phone that changes its mac address - probably for some privacy reason or for some hacking reason (maybe stealing mac addresses to steal the identity).
If I would have such device in my networks, I would not allow to log in for it.
If you want to give it fixed ip, you can try to create fixed lease record with zeroes in mac address but use ClientID if it is fixed. Better make mac not changing on the android device…
I thought that you could use also hostname, but it seems it is not possible.