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.