What Do Firewalls Really Do?

Firewalls are a mainstay of network security. At its core, the firewall acts as a barrier between a trusted internal network and untrusted external networks, such as the Internet. Its primary function is to monitor and control incoming and outgoing network traffic based on predetermined security rules. Think of the firewall as a gatekeeper scrutinizing every packet of data that attempts to pass through. Let’s take a look at the different types of firewalls and some of their key functions.

Types of Firewalls

Firewalls come in various forms, catering to different security needs and network configurations. Here are some common types:

• Packet Filtering Firewalls - These are the most basic types of firewalls that inspect individual packets of data based on predetermined criteria, such as IP addresses, port numbers, and protocols.
• Stateful Inspection Firewalls - Unlike packet filtering firewalls, stateful inspection firewalls keep track of the state of active connections. They analyze the context of packets within the context of ongoing connections, enhancing security by understanding the relationship between packets.
• Proxy Firewall - Proxy firewalls act as intermediaries between internal and external systems. They receive requests from clients, forward them to the destination, and then relay the response back to the clients. This setup adds an additional layer of security by hiding the internal network's details.
• Next-Generation Firewalls (NGFW) - NGFWs combine traditional firewall capabilities with advanced features such as intrusion detection and prevention, application awareness, and deep packet inspection. They offer more granular control over network traffic and are adept at combating sophisticated threats.

Key Functions of a Firewall

Let’s take a look at some of the main features of firewalls. 

• Access Control - Firewalls enforce access control policies to determine which network traffic is allowed to pass through and which should be blocked. This helps prevent unauthorized access to sensitive resources.
• Traffic Filtering - By inspecting network packets, firewalls can filter out malicious or suspicious content, such as malware, viruses, and phishing attempts. They also block unauthorized access attempts, such as port scans and denial-of-service (DoS) attacks.
• Network Address Translation (NAT) - Many firewalls perform NAT, which translates private IP addresses used within a local network into public IP addresses visible on the internet. This helps conserve IPv4 addresses and adds a layer of obscurity to internal network devices.
• Logging and Monitoring - Firewalls maintain logs of network activities, including allowed and blocked traffic, security events, and policy violations. Monitoring these logs enables administrators to identify security incidents and successfully manage network security.

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