Intruder on my Network

Good day friends

i had a serious confusion today at work… hmmm what an experience, i have a RB1100AH router with my network settings okay.
a colleague of mine brought a small dlink router, all in the name connecting his personal phone, tab and laptop. He connected it to my LAN only for the router to divide the net work into two(2) that was were my problem all started. my network dhcp is 10.10.1.0/24 and new router dhcp was 192.168.1.0/24. only those under my dhcp could reach the internet while the other on that 192.168.1.0 segment had destination unreachable. i kept on troubleshooting for hours etc..


now my question is how do i set my mikrotik router to be able to take charge or rather not to allow any dhcp service on the LAN to take place its own dhcp server. is it possible???