1)192.168.1.1
2)user admin password admin (Refer ur router)
3)Search for Nat it is mostly in Advanced option
4)Check DMZ: DMZ Host IP Address 192.168.1.2 ( Local IP Address ) (But DMZ will open all the ports)
5)To open a particular port search virtual server
Rule Application Protocol Start Port End Port Local IP Address
1 FTP ALL 21 21 192.168.1.2