To get the details of your own systems, begin by finding your network interfaces. You can find the interfaces on your machines and the addresses associated with them by typing:
ip -4 addr show scope global
returns
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
inet 198.51.100.45/18 brd 45.55.191.255 scope global eth0
valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
inet 192.168.1.5/16 brd 10.132.255.255 scope global eth1
valid_lft forever preferred_lft forever
The highlighted output above shows two interfaces (eth0 and eth1) and the addresses assigned to each.
To find out which of these interfaces is your public interface, type:
ip route show | grep default
Returns
default via 111.111.111.111 dev <color red>eth0</color>
The interface shown (eth0 in this example) will be the interface connected to your default gateway. This is almost certainly your public interface.