For ssh and ping to local machines with out the .local extension I added them to my /ets/hosts file.
A normal user does not have permission so you have to use sudo. If you os x account has admin privlages it will prompt you for your password. If you have not used vim before, i for insert mode (like a standard text editor), esc to exit insert mode and :wq to write and quit.
sudo vim /etc/hosts ## # Host Database # # localhost is used to configure the loopback interface # when the system is booting. Do not change this entry. ## 127.0.0.1 localhost 255.255.255.255 broadcasthost ::1 localhost fe80::1%lo0 localhost ## Append Local fixed ip Machines 192.168.10.1 router 192.168.10.100 macmini 192.168.10.101 krypton 192.168.10.250 backup