How can you determine which ports are open on a server and which IP addresses are connecting to them?

To identify open ports on a server and the IP addresses connecting to them, you can use the following tools:

• netstat: shows active connections and listening ports.

  netstat -tulnp
  

  -t — TCP, -u — UDP, -l — listening, -n — show port numbers, -p — process

• ss — a modern alternative to netstat:

  ss -tulnp
  

• lsof — shows open files and ports:

  lsof -i -P -n
  

• For scanning ports from outside, you can use nmap:

  nmap -sT localhost
  

These commands will help you see which ports are open, which processes are using them, and the IP addresses of connections.