Firewall (computing)

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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]

Contents

History

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 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 1980s. Because they already segregated networks, routers could apply filtering to packets crossing them. [7]

Before it was used in real-life computing, the term appeared in John Badham's 1983 computer‑hacking movie WarGames , spoken by the bearded and bespectacled programmer named Paul Richter, which possibly inspired its later use. [8]

One of the earliest commercially successful firewall and network address translation (NAT) products was the PIX (Private Internet eXchange) Firewall, invented in 1994 by Network Translation Inc., a startup founded and run by John Mayes. The PIX Firewall technology was coded by Brantley Coile as a consultant software developer. [9] Recognizing the emerging IPv4 address depletion problem, they designed the PIX to enable organizations to securely connect private networks to the public internet using a limited number of registered IP addresses. The innovative PIX solution quickly gained industry acclaim, earning the prestigious "Hot Product of the Year" award from Data Communications Magazine in January 1995. Cisco Systems, seeking to expand into the rapidly growing network security market, subsequently acquired Network Translation Inc. in November 1995 to obtain the rights to the PIX technology. The PIX became one of Cisco's flagship firewall product lines before eventually being succeeded by the Adaptive Security Appliance (ASA) platform introduced in 2005.

Types of firewall

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), [10] their basic function being 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 [11] [12] or VPN [13] services. Host-based firewalls are deployed directly on the host itself to control network traffic or other computing resources. [14] [15] This can be a daemon or service as a part of the operating system or an agent application for protection.

An illustration of a network-based firewall within a network Firewall.png
An illustration of a network-based firewall within a network

Packet filter

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. [16] 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. [17] [18]

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. [19] In 1992, Steven McCanne and Van Jacobson released a paper on BSD Packet Filter (BPF) while at Lawrence Berkeley Laboratory. [20] [21]

Connection tracking

Flow of network packets through Netfilter, a Linux kernel module Netfilter-packet-flow.svg
Flow of network packets through Netfilter, a Linux kernel module

From 1989–1990, three colleagues from AT&T Bell Laboratories, Dave Presotto, Janardan Sharma, and Kshitij Nigam, developed the second generation of firewalls, calling them circuit-level gateways. [22]

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. [23]

Application layer

Marcus Ranum, Wei Xu, and Peter Churchyard released an application firewall known as Firewall Toolkit (FWTK) in October 1993. [24] This became the basis for Gauntlet firewall at Trusted Information Systems. [25] [26]

The key benefit of application layer filtering is that it can understand certain applications and protocols such as File Transfer Protocol (FTP), Domain Name System (DNS), or Hypertext Transfer Protocol (HTTP). This allows it to identify unwanted applications or services using a non standard port, or detect if an allowed protocol is being abused. [27] It can also provide unified security management including enforced encrypted DNS and virtual private networking. [28] [29] [30]

As of 2012, the next-generation firewall provides a wider range of inspection at the application layer, extending deep packet inspection functionality to include, but is not limited to:

Endpoint specific

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 Policies

At the core of a firewall's operation are the policies that govern its decision-making process. These policies, collectively known as firewall rules, are the specific guidelines that determine the traffic allowed or blocked across a network's boundaries. [32] [33]

Firewall rules are based on the evaluation of network packets against predetermined security criteria. A network packet, which carries data across networks, must match certain attributes defined in a rule to be allowed through the firewall. These attributes commonly include:

Zones

Zones are logical segments within a network that group together devices with similar security requirements. By partitioning a network into zones, such as "Technical", "WAN", "LAN", "Public," "Private," "DMZ", and "Wireless," administrators can enforce policies that control the flow of traffic between them. Each zone has its own level of trust and is governed by specific firewall rules that regulate the ingress and egress of data.

I typical default is to allow all traffic from LAN to WAN, and to drop all traffic from WAN to LAN.

Services

In networking terms, services are specific functions typically identified by a network port and protocol. Common examples include HTTP/HTTPS (web traffic) on ports 80 and 443, FTP (file transfer) on port 21, and SMTP (email) on port 25. Services are the engines behind the applications users depend on. From a security aspect, controlling access to services is crucial because services are common targets for exploitation. Firewalls employ rules that stipulate which services should be accessible, to whom, and in what context. For example, a firewall might be configured to block incoming FTP requests to prevent unauthorized file uploads but allow outgoing HTTPS requests for web browsing.

Applications

Applications refer to the software systems that users interact with while on the network. They can range from web browsers and email clients to complex database systems and cloud-based services. In network security, applications are important because different types of traffic can pose varying security risks. Thus, firewall rules can be crafted to identify and control traffic based on the application generating or receiving it. By using application awareness, firewalls can allow, deny, or limit traffic for specific applications according to organisational policies and compliance requirements, thereby mitigating potential threats from vulnerable or undesired applications.

Application can both be a grouping of services, or a L7 inspection.

USER ID

Implementing firewall rules based on IP addresses alone is often insufficient due to the dynamic nature of user location and device usage. [34] [35] User ID will be translate to a IP address.

This is where the concept of "User ID" makes a significant impact. User ID allows firewall rules to be crafted based on individual user identities, rather than just fixed source or destination IP addresses. This enhances security by enabling more granular control over who can access certain network resources, regardless of where they are connecting from or what device they are using.

The User ID technology is typically integrated into firewall systems through the use of directory services such as Active Directory, LDAP, RADIUS or TACACS+. These services link the user's login information to their network activities. By doing this, the firewall can apply rules and policies that correspond to user groups, roles, or individual user accounts instead of purely relying on the network topology.

Example of Using User ID in Firewall Rules

Consider an school that wants to restrict access to a social media server from students. They can create a rule in the firewall that utilises User ID information to enforce this policy.

  1. Directory Service Configuration — First, the firewall must be configured to communicate with the directory service that stores user group memberships. In this case, an Active Directory server.
  2. User Identification — The firewall maps network traffic to specific user IDs by interpreting authentication logs. When a user logs on, the firewall associates that login with the user's IP address.
  3. Define User Groups — Within the firewall's management interface, define user groups based on the directory service. For example, create groups such as "Students".
  4. Create Firewall Rule:
    • Source: User ID (e.g., Students)
    • Destination: list of IP addresses
    • Service/Application: Allowed services (e.g., HTTP, HTTPS)
    • Action: Deny
  5. Implement Default Allow Rule:
    • Source: LAN zone
    • Destination: WAN zone
    • Service/Application: Any
    • Action: Allow

With this setup, only users who authenticate and are identified as members of "Students" are deny to access social media servers. All other traffic, starting from LAN interfaces, will be allowed.

Most common firewall log types

Traffic Logs:

Threat Prevention Logs:

Audit Logs:

Event Logs:

Session Logs:

DDoS Mitigation Logs:

Geo-location Logs:

URL Filtering Logs:

User Activity Logs:

VPN Logs:

System Logs:

Compliance Logs:

Configuration

Setting up a firewall is a complex and error-prone task. A network may face security issues due to configuration errors. [36]

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. [37]

See also

Related Research Articles

<span class="mw-page-title-main">Network address translation</span> Technique for making connections between IP address spaces

Network address translation (NAT) is a method of mapping an IP address space into another by modifying network address information in the IP header of packets while they are in transit across a traffic routing device. The technique was initially used to bypass the need to assign a new address to every host when a network was moved, or when the upstream Internet service provider was replaced but could not route the network's address space. It has become a popular and essential tool in conserving global address space in the face of IPv4 address exhaustion. One Internet-routable IP address of a NAT gateway can be used for an entire private network.

<span class="mw-page-title-main">Proxy server</span> Computer server that makes and receives requests on behalf of a user

In computer networking, a proxy server is a server application that acts as an intermediary between a client requesting a resource and the server providing that resource. It improves privacy, security, and possibly performance in the process.

In computer security, a DMZ or demilitarized zone is a physical or logical subnetwork that contains and exposes an organization's external-facing services to an untrusted, usually larger, network such as the Internet. The purpose of a DMZ is to add an additional layer of security to an organization's local area network (LAN): an external network node can access only what is exposed in the DMZ, while the rest of the organization's network is protected behind a firewall. The DMZ functions as a small, isolated network positioned between the Internet and the private network.

In computing, a stateful firewall is a network-based firewall that individually tracks sessions of network connections traversing it. Stateful packet inspection, also referred to as dynamic packet filtering, is a security feature often used in non-commercial and business networks.

Deep packet inspection (DPI) is a type of data processing that inspects in detail the data being sent over a computer network, and may take actions such as alerting, blocking, re-routing, or logging it accordingly. Deep packet inspection is often used for baselining application behavior, analyzing network usage, troubleshooting network performance, ensuring that data is in the correct format, checking for malicious code, eavesdropping, and internet censorship, among other purposes. There are multiple headers for IP packets; network equipment only needs to use the first of these for normal operation, but use of the second header is normally considered to be shallow packet inspection despite this definition.

<span class="mw-page-title-main">Port forwarding</span> Computer networking feature

In computer networking, port forwarding or port mapping is an application of network address translation (NAT) that redirects a communication request from one address and port number combination to another while the packets are traversing a network gateway, such as a router or firewall. This technique is most commonly used to make services on a host residing on a protected or masqueraded (internal) network available to hosts on the opposite side of the gateway, by remapping the destination IP address and port number of the communication to an internal host.

Internet security is a branch of computer security. It encompasses the Internet, browser security, web site security, and network security as it applies to other applications or operating systems as a whole. Its objective is to establish rules and measures to use against attacks over the Internet. The Internet is an inherently insecure channel for information exchange, with high risk of intrusion or fraud, such as phishing, online viruses, trojans, ransomware and worms.

An application firewall is a form of firewall that controls input/output or system calls of an application or service. It operates by monitoring and blocking communications based on a configured policy, generally with predefined rule sets to choose from. The two primary categories of application firewalls are network-based and host-based.

Cisco PIX was a popular IP firewall and network address translation (NAT) appliance. It was one of the first products in this market segment.

Netfilter is a framework provided by the Linux kernel that allows various networking-related operations to be implemented in the form of customized handlers. Netfilter offers various functions and operations for packet filtering, network address translation, and port translation, which provide the functionality required for directing packets through a network and prohibiting packets from reaching sensitive locations within a network.

In computer networks, a tunneling protocol is a communication protocol which allows for the movement of data from one network to another. It can, for example, allow private network communications to be sent across a public network, or for one network protocol to be carried over an incompatible network, through a process called encapsulation.

A session border controller (SBC) is a network element deployed to protect SIP based voice over Internet Protocol (VoIP) networks.

Network address translation traversal is a computer networking technique of establishing and maintaining Internet Protocol connections across gateways that implement network address translation (NAT).

<span class="mw-page-title-main">Windows Firewall</span> Firewall software for Windows

Windows Firewall is a firewall component of Microsoft Windows. It was first included in Windows XP SP2 and Windows Server 2003 SP1. Before the release of Windows XP Service Pack 2, it was known as the "Internet Connection Firewall."

Windows Filtering Platform (WFP) is a set of system services in Windows Vista and later that allows Windows software to process and filter network traffic. Microsoft intended WFP for use by firewalls, antimalware software, and parental controls apps. Additionally, WFP is used to implement NAT and to store IPSec policy configuration.

An application-level gateway is a security component that augments a firewall or NAT employed in a mobile network. It allows customized NAT traversal filters to be plugged into the gateway to support address and port translation for certain application layer "control/data" protocols such as FTP, BitTorrent, SIP, RTSP, file transfer in IM applications. In order for these protocols to work through NAT or a firewall, either the application has to know about an address/port number combination that allows incoming packets, or the NAT has to monitor the control traffic and open up port mappings dynamically as required. Legitimate application data can thus be passed through the security checks of the firewall or NAT that would have otherwise restricted the traffic for not meeting its limited filter criteria.

There are a number of security and safety features new to Windows Vista, most of which are not available in any prior Microsoft Windows operating system release.

In computing, Microsoft's Windows Vista and Windows Server 2008 introduced in 2007/2008 a new networking stack named Next Generation TCP/IP stack, to improve on the previous stack in several ways. The stack includes native implementation of IPv6, as well as a complete overhaul of IPv4. The new TCP/IP stack uses a new method to store configuration settings that enables more dynamic control and does not require a computer restart after a change in settings. The new stack, implemented as a dual-stack model, depends on a strong host-model and features an infrastructure to enable more modular components that one can dynamically insert and remove.

A distributed firewall is a security application on a host machine of a network that protects the servers and user machines of its enterprise's networks against unwanted intrusion. A firewall is a system or group of systems that implements a set of security rules to enforce access control between two networks to protect the "inside" network from the "outside" network. They filter all traffic regardless of its origin—the Internet or the internal network. Usually deployed behind the traditional firewall, they provide a second layer of defense. The advantages of the distributed firewall allow security rules (policies) to be defined and pushed out on an enterprise-wide basis, which is necessary for larger enterprises.

A next-generation firewall (NGFW) is a part of the third generation of firewall technology, combining a conventional firewall with other network device filtering functions, such as an application firewall using in-line deep packet inspection (DPI), an intrusion prevention system (IPS). Other techniques might also be employed, such as TLS-encrypted traffic inspection, website filtering, QoS/bandwidth management, antivirus inspection, third-party identity management integration, and SSL decryption

References

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