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Monica Gallardo
In computing, a firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules.[1][2] A firewall typically establishes a barrier between a trusted network and an untrusted network, such as the Internet.[3]
The term firewall originally referred to a wall intended to confine a fire within a line of adjacent buildings.[4] Later uses refer to similar structures, such as the metal sheet separating the engine compartment of a vehicle or aircraft from the passenger compartment. The term was applied in the late 1980s to network technology[5] that emerged when the Internet was fairly new in terms of its global use and connectivity.[6] The predecessors to firewalls for network security were routers used in the late 1980s. Because they already segregated networks, routers could apply filtering to packets crossing them.[7]
Firewalls are categorized as a network-based or a host-based system. Network-based firewalls are positioned between two or more networks, typically between the local area network (LAN) and wide area network (WAN),[9] their basic function is to control the flow of data between connected networks. They are either a software appliance running on general-purpose hardware, a hardware appliance running on special-purpose hardware, or a virtual appliance running on a virtual host controlled by a hypervisor. Firewall appliances may also offer non-firewall functionality, such as DHCP[10][11] or VPN[12] services. Host-based firewalls are deployed directly on the host itself to control network traffic or other computing resources.[13][14] This can be a daemon or service as a part of the operating system or an agent application for protection.
The first reported type of network firewall is called a packet filter, which inspects packets transferred between computers. The firewall maintains an access-control list which dictates what packets will be looked at and what action should be applied, if any, with the default action set to silent discard. Three basic actions regarding the packet consist of a silent discard, discard with Internet Control Message Protocol or TCP reset response to the sender, and forward to the next hop.[15] Packets may be filtered by source and destination IP addresses, protocol, or source and destination ports. The bulk of Internet communication in 20th and early 21st century used either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) in conjunction with well-known ports, enabling firewalls of that era to distinguish between specific types of traffic such as web browsing, remote printing, email transmission, and file transfers.[16][17]
The first paper published on firewall technology was in 1987 when engineers from Digital Equipment Corporation (DEC) developed filter systems known as packet filter firewalls. At AT&T Bell Labs, Bill Cheswick and Steve Bellovin continued their research in packet filtering and developed a working model for their own company based on their original first-generation architecture.[18] In 1992, Steven McCanne andVan Jacobson released a paper on BSD Packet Filter (BPF) while at Lawrence Berkeley Laboratory.[19][20]
Second-generation firewalls perform the work of their first-generation predecessors but also maintain knowledge of specific conversations between endpoints by remembering which port number the two IP addresses are using at layer 4 (transport layer) of the OSI model for their conversation, allowing examination of the overall exchange between the nodes.[22]
Marcus Ranum, Wei Xu, and Peter Churchyard released an application firewall known as Firewall Toolkit (FWTK) in October 1993.[23] This became the basis for Gauntlet firewall at Trusted Information Systems.[24][25]
Endpoint-based application firewalls function by determining whether a process should accept any given connection. Application firewalls filter connections by examining the process ID of data packets against a rule set for the local process involved in the data transmission. Application firewalls accomplish their function by hooking into socket calls to filter the connections between the application layer and the lower layers. Application firewalls that hook into socket calls are also referred to as socket filters.[citation needed]
Firewall policy configuration is based on specific network type (e.g., public or private), and can be set up using firewall rules that either block or allow access to prevent potential attacks from hackers or malware.[31]
Network layer or packet filters inspect packets at a relatively low level of the TCP/IP protocol stack, not allowing packets to pass through the firewall unless they match the established rule set where the source and destination of the rule set is based upon Internet Protocol (IP) addresses and ports. Firewalls that do network layer inspection perform better than similar devices that do application layer inspection. The downside is that unwanted applications or malware can pass over allowed ports, e.g. outbound Internet traffic over web protocols HTTP and HTTPS, port 80 and 443 respectively.
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.
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.
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.
A virtual firewall is typically deployed as a virtual appliance in a private 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).
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.
Most commercially available firewall products, both hardware and software based, come preconfigured and ready to use. Since each firewall is different, you will need to read and understand the documentation that comes with it to determine whether the default firewall settings are sufficient for your needs. This is particularly concerning because the "default" configuration is typically less restrictive, which could make your firewall more susceptible to compromise. Alerts about current malicious activity (e.g., CISA's Alerts) sometimes include information about restrictions you can implement through your firewall.
Though properly configured firewalls may effectively block some attacks, do not be lulled into a false sense of security. Firewalls do not guarantee that your computer will not be attacked. Firewalls primarily help protect against malicious traffic, not against malicious programs (i.e., malware), and may not protect you if you accidentally install or run malware on your computer. However, using a firewall in conjunction with other protective measures (e.g., antivirus software and safe computing practices) will strengthen your resistance to attacks. (See Good Security Habits for more information.)
A firewall in a computer network provides security at the perimeter by monitoring incoming and outgoing data packets in network traffic for malware and anomalies. A firewall filters traffic as it attempts to enter and exit your network as opposed to antivirus software that scans devices and storage systems on the network for threats that have penetrated your defenses.
Depending on where it is deployed and its purpose, a firewall can be delivered as a hardware appliance, as software, or software as a service (SaaS). There are five main types of firewalls depending upon their operational method:
Firewall security has been around since the 1980s. Originally, it only consisted of packet filters and existed within networks designed to examine the packets of data sent and received between computers. Since then, firewalls have evolved in response to the growing variety of threats:
Basically, there are two types of delivery methods for firewalls: software or hardware. In general, a software firewall protects the host it runs on such as a computer or device, and a hardware firewall protects the network.
The most common kind of software firewall can be found on most personal computers. The firewall works by inspecting data packets that flow to and from your device. It compares the information in the data packets against a list of threat signatures. If a data packet matches the profile of a known threat, it is discarded.
Infrequently, software firewalls are used in corporate settings to provide an added layer of protection. Software firewalls also can monitor different programs running on the host, while filtering inbound and outbound traffic. This provides granular control, enabling the firewall to allow communications to and from one program but prevent communications to and from another.
Network firewalls monitor traffic by performing deep packet inspection and packet filtering. If the content of a data packet does not meet previously selected criteria based on rules set by the network administrator or security team, the network firewall rejects and blocks that traffic.
Originally, firewalls were divided into two camps: proxy and stateful. Over time, stateful inspection became more sophisticated and the performance of proxy firewalls became too slow., Today, nearly all firewalls are stateful and divide into two general types: network firewalls and host-based firewalls.
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