Before we discuss firewalls in detail, you must understand the basic terminology:
- IP Address: An IP address is a host identity on the internet through which reachability is achieved via a routing protocol between networks. There are two types of IP address available—IPv4 (32 bit with class A, B, C, or D) and IPv6 (128 bit with unicast address, any cast address, or multicast address). For example, IPv4: 200.10.20.1 and IPv6: 2001:0db8:85a3:0000:0000:8a2e:0370:7334
- Ports: Any application that is hosted on an operating system makes its service available on a network using standard ports. When accessing any application on the internet, a dynamic port is opened on source and a standard known port for destination. For example, HTTP uses port 80, FTP uses port 22, and Telnet uses port 23.
- Protocol: A protocol is a standard method and mutual agreement for exchanging data over a network host on a local area network, internet, intranet, and WAN.
- Tuples: The term 5-tuple refers to the five items (source and destination IP, source and destination port, and protocol) in any given IP packet. The firewall policy uses these tuples to define the firewall rule of whether to block or allow traffic.