Add user filtering with AllowUsers option in sshd_config file:
AllowUsers johndoe@192.168.1.* admin2@192.168.1.* otherid1 otherid2
This allows johndoe and admin2 only from 192.168.1.* addresses and otherid1, otherid2 from anywhere.
Impact of procedure : Performing the following procedure should not have a negative impact on your system. Open putty by double click...