Using netstat, it is possible to see the current state of sockets on hosts.
For Linux, it may be necessary to install net-tools via package manager:
sudo apt install net-tools
Then, the outcome has the following format:
$ netstat -an
Active Internet connections (including servers)
Proto Recv-Q Send-Q Local Address Foreign Address (state)
tcp 0 0 127.0.0.1.65432 *.*
Proto as tcp indicates IPv4 IP address family.