Day 4: Working of a firewall

What comes to your mind when you see this?! Honestly me it's a "firewall" and am sure most of you thought so. 
When we come to the computing world, this is a metaphor for a firewall which is  a system designed to prevent unauthorized access to or from a private network. 
A firewall can be both a software and a hardware. Many people might be familiar of the software but hardware firewalls also exist! Many companies do have them in supply. 

These are examples of firewalls from the prominent network distributors l know. 
Firewalls can also be grouped in categories ie,

•  Packet-filtering firewalls;

   Used to control network access by monitoring outgoing and incoming packets and allowing them to pass or halt based on the source and destination Internet Protocol (IP) addresses, protocols and ports.

•  Stateful inspection firewalls (Dynamic packet filtering) 

Monitors the state of active connections and uses this information to determine which network packets to allow through the firewall.

•   Circuit-level gateways;

 These work at the session layer of the OSI model, or as a "shim-layer" between the application layer and the transport layer of the TCP/IP stack. They monitor TCP handshaking between packets to determine whether a requested session is legitimate.

•   Application-level gateways (a.k.a. proxy firewalls);

 Provides network security. It filters incoming node traffic to certain specifications which mean that only transmitted network application data is filtered.

•   Next-gen firewall;

 This is a deep-packet inspection firewall that moves beyond port/protocol inspection and blocking to add application-level inspection, intrusion prevention, and bringing intelligence from outside the firewall.

I hope that catches you up on firewalls.