What Is a Firewall? (2024)

Cisco named Best Next Generation Firewall (NGFW) in SE Labs Annual Report 2023

A firewall is a network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules.

Firewalls have been a first line of defense in network security for over 25 years. They establish a barrier between secured and controlled internal networks that can be trusted and untrusted outside networks, such as the Internet.

A firewall can be hardware, software, software-as-a service (SaaS), public cloud, or private cloud (virtual).

Cisco Secure Firewall Overview (1:42)
Cisco Secure Firewall

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The Total Economic Impact of Cisco Secure Firewall

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Different types of firewalls

Proxy firewall

An early type of firewall device, a proxy firewall serves as the gateway from one network to another for a specific application. Proxy servers can provide additional functionality such as content caching and security by preventing direct connections from outside the network. However, this also may impact throughput capabilities and the applications they can support.

Stateful inspection firewall

Now thought of as a “traditional” firewall, a stateful inspection firewall allows or blocks traffic based on state, port, and protocol. It monitors all activity from the opening of a connection until it is closed. Filtering decisions are made based on both administrator-defined rules as well as context, which refers to using information from previous connections and packets belonging to the same connection.

Unified threat management (UTM) firewall

A UTM device typically combines, in a loosely coupled way, the functions of a stateful inspection firewall with intrusion prevention and antivirus. It may also include additional services and often cloud management. UTMs focus on simplicity and ease of use.

See our UTM devices.

Next-generation firewall (NGFW)

Firewalls have evolved beyond simple packet filtering and stateful inspection. Most companies are deploying next-generation firewalls to block modern threats such as advanced malware and application-layer attacks.

According to Gartner, Inc.’s definition, a next-generation firewall must include:

Threat-focused NGFW

These firewalls include all the capabilities of a traditional NGFW and also provide advanced threat detection and remediation. With a threat-focused NGFW you can:

Know which assets are most at risk with complete context awareness
Quickly react to attacks with intelligent security automation that sets policies and hardens your defenses dynamically
Better detect evasive or suspicious activity with network and endpoint event correlation
Greatly decrease the time from detection to cleanup with retrospective security that continuously monitors for suspicious activity and behavior even after initial inspection
Ease administration and reduce complexity with unified policies that protect across the entire attack continuum

Learn about our threat-focused firewalls.

See, try or buy a firewall.

Virtual firewall

A virtual firewall is typically deployed as a virtual appliance inaprivate cloud (VMware ESXi, Microsoft Hyper-V, KVM) or public cloud (Amazon Web Services or AWS, Microsoft Azure, Google Cloud Platform or GCP, Oracle Cloud Infrastructure or OCI) to monitor and secure traffic across physical and virtual networks.A virtual firewall is often a key component in software-defined networks (SDN).

Learn about Cisco virtual firewalls forpublic cloudandprivate cloud.

Cloud Native Firewall

Cloud native firewalls are modernizing the way to secure applications and workload infrastructure at scale. With automated scaling features, cloud native firewalls enable networking operations and security operations teams to run at agile speeds.

Advantages of Cloud Native Firewalls