On R2 stop mac addresses 0c00.xxxx.xxxy, where ymod4=0 (0c00.xxxx.xxx0, 0c00.xxxx.xxx4, 0c00.xxxx.xxx8, 
0c00.xxxx.xxxd)) from coming in on Serial1/2

**********************************************************************************************

R2#sh run | b interface Serial1/2
interface Serial1/2
 no ip address
 clock rate 128000
 bridge-group 1
 bridge-group 1 input-address-list 700
!

!
access-list 700 deny   0c00.0000.0000   0000.ffff.fffc
access-list 700 permit 0000.0000.0000   ffff.ffff.ffff
!