Firewall (Server)


A server’s firewall controls what kind of Internet connections is allowed to flow in (inbound) and out (outbound) of a server.

For inbound and outbound traffic, the server’s owner can specify the traffic rule by specifying:

  • What type of protocol (http, SMTP, SQL)
  • What port
  • A set of allowed IPs


  • Military security checkpoint: it controls who can enter and leave the military building.