Hi i am using mt router os for authentication i also bind mac address on login id
but some clients spoofing other clients mac address and he is using other clients bandwidth and my dhcp server also leases same ip are both clients please help me.

i am using router os 2.9.27

I have the same problem but it seems that no one has a solution for this isue and no one say if this is a bug or loss of setting...
only one says upgrade to version 3.1 router os.....
I don't know why no one want to talk about this....
I only want to know if there is a solution for this or not...
this the link of my post http://forum.mikrotik.com/viewtopic.php?f=2&t=21457

It is quite simple, when you use 2.9.27 it is highly suspicious that you are running cracked version, so, people are less willing to help.

The actual problem is that you are trying to use technology you do not understand well. What you have as a problem is very basic thing: you relay on MAC addresses and MAC addresses may be spoofed. This has nothing to do with MT, it cannot see if reported MAC is real physical MAC or spoofed one.

What you have to do, is to set hotspot or VPN or think up some other way to authenticate user which requires him to type in his password to gain access.