I can't do PING between machines (server and agent)

I can't do PING between machines (server and agent). I have 2 machines in VirtualBox in NAT. I have this configuration.

file server --> /etc/network/interfaces

iface enp0s3 inet static
	address	192.168.1.100
	netmask	255.255.255.0	
	network	192.168.1.0	
	broadcast 192.168.1.255
	gateway	192.168.1.1

Then I restart service network --> /etc/init.d/networking restart
I down and up enp0s3.
And if I do ifconfig I have default IP (10.0.2.15) ¿Why have I this IP? ¿Why don't change it?
But if I write in the browser http://192.168.1.100/ocsreports it find it

file agent --> /etc/network/interfaces

iface enp0s3 inet static
	address	192.168.1.101
	netmask	255.255.255.0	
	network	192.168.1.0	
	broadcast 192.168.1.255
	gateway	192.168.1.1

Then I do the same and I have the same error.I have 10.0.2.15(IP default)