What is Firewall ? | Firewall installation in Pakistan | what is the main Purpose of firewall?

What is Firewall ? | Firewall installation in Pakistan | what is main Purpose of firewall ? |Reality
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Firewall - meaning and definition
A firewall is a computer network security system that restricts internet traffic in to, out of, or within a private network.
This software or dedicated hardware-software unit functions by selectively blocking or allowing data packets. It is typically intended to help prevent malicious activity and to prevent anyone-inside or outside a private network-from engaging in unauthorized web activities.
What is a firewall?
Firewalls can be viewed as gated borders or gateways that manage the travel of permitted and prohibited web activity in a private network. The term comes from the concept of physical walls being barriers to slow the spread of fire until emergency services can extinguish it. By comparison, network security firewalls are for web traffic management - typically intended to slow the spread of web threats.
Firewalls create 'choke points' to funnel web traffic, at which they are then reviewed on a set of programmed parameters and acted upon accordingly. Some firewalls also track the traffic and connections in audit logs to reference what has been allowed or blocked.
Firewalls are typically used to gate the borders of a private network or its host devices. As such, firewalls are one security tool in the broader category of user access control. These barriers are typically set up in two locations - on dedicated computers on the network or the user computers and other endpoints themselves (hosts).
How do firewalls work?
A firewall decides which network traffic is allowed to pass through and which traffic is deemed dangerous. Essentially, it works by filtering out the good from the bad, or the trusted from the untrusted. However, before we go into detail, it helps to understand the structure of web-based networks.
Firewalls are intended to secure private networks and the endpoint devices within them, known as network hosts. Network hosts are devices that ‘talk’ with other hosts on the network. They send and receive between internal networks, as well as outbound and inbound between external networks.
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External public networks typically refer to the public/global internet or various extranets.
Internal private network defines a home network, corporate intranets, and other ‘closed’ networks.
Perimeter networks detail border networks made of bastion hosts - computer hosts dedicated with hardened security that are ready to endure an external attack.
Types of firewall
Different types of firewalls incorporate varied methods of filtering. While each type was developed to surpass previous generations of firewalls, much of the core technology has passed between generations.
Firewall types are distinguished by their approach to:
Connection tracking
Filtering rules
Audit logs
Each type operates at a different level of the standardized communications model, the Open Systems Interconnection model (OSI). This model gives a better visual of how each firewall interacts with connections.
Static Packet-Filtering Firewall
Static packet-filtering firewalls, also known as stateless inspection firewalls, operate at the OSI network layer (layer 3). These offer basic filtering by checking all individual data packets sent across a network, based on where they're from and where they're attempting to go. Notably, previously accepted connections are not tracked. This means each connection must be re-approved with every data packet sent.
Filtering is based on IP addresses, ports, and packet rotection.
Circuit-Level Gateway Firewall
Circuit-level gateways operate on the session level (layer 5). These firewalls check for functional packets in an attempted connection, and-if operating well-will permit a persistent open connection between the two networks. The firewall stops supervising the connection after this occurs.
The ongoing unmonitored connection is dangerous, as legitimate means could open the connection and later permit a malicious actor to enter uninterrupted.
Stateful Inspection Firewall
Stateful inspection firewalls, also called dynamic packet-filtering firewalls, are unique from static filtering in their ability to monitor ongoing connections and remember past ones. These began by operating on the transport layer (layer 4) but nowadays, these firewalls can monitor many layers, including the application layer (layer 7).
This firewall updates filtering rules based on past connection events logged in the state table by the screening router.
Proxy Firewall
Proxy Firewalls, also known as application-level firewalls (layer 7), are unique in reading and filtering application protocols. These combine application-level inspection, or ‘deep packet inspection (DPI),’ and stateful inspection.
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