Perimeter Firewall: What Is It, and How Does It Work?

Over 30 years ago, the concept of a firewall entered the IT security conversation. Even today, the technology still plays a vital role in enterprise security, facilitating secure connectivity between different networks. As a mechanism of filtering out malicious traffic before it crosses from a public network into a private network, a perimeter firewall has ascertained its merit over the decades.

As with any persistent technology, it has obviously spawned many iterations. Discover how a perimeter firewall prevents network intrusions in this post.

What Is a Perimeter Firewall?

A perimeter firewall is a security application that defends the boundary between an organization’s private network from public networks such as the internet. You can implement a perimeter firewall as either software, hardware or both to act as the first line of defense in enterprise security. When implemented, a perimeter firewall inspects packets coming in and out of a private network and either allows or blocks them based on pre-determined rules.

These rules—defined in access control lists (ACLs)—specify what network names, internet protocol (IP) addresses, and port numbers are permitted. You can configure these rules to control inbound and outbound traffic as shown below:

Perimeter Firewall: What Is It, and How Does It Work?
The primary goal of installing a perimeter firewall is to guard against external attacks. You can also install them within the organization’s network to create segmentation and thwart insider threats. Besides providing the first line of defense against attacks, perimeter firewalls can also record logging and audit events. Network administrators can use these records to identify user patterns and enhance rule sets.

What Is a Network Perimeter?

The terminologies network perimeter and firewall are sometimes used interchangeably, albeit with different meanings. A network perimeter is the edge of an organization’s internal network. It is the boundary between a company’s internal network and public networks such as the internet—or any uncontrolled external network.

A firewall, in contrast, is part of the network perimeter whose goal is to filter out malicious traffic before it crosses the boundary from a public network into an organization’s internal network. Besides a firewall, other components of a network perimeter include:

How Does a Perimeter Firewall Work?

As the primary defense line against attacks, perimeter firewalls employ different techniques to control traffic between an organization’s network and untrusted networks. Let’s discuss a few of them.

Static packet filtering

Static packet filtering is a technique where the firewall filters traffic based on packet fields and the network administrator’s rules. A static packet filter examines each packet it receives and compares it against ACLs. It then accepts or blocks the traffic into the organization’s network based on what the rule specifies.

Static packet filtering is among the oldest firewall techniques and operates at layers three and four of the open systems interconnection (OSI) model. As such, it cannot differentiate between the application layer protocols. It also cannot prevent spoofing attacks.

Proxy-based firewalls

A proxy-based firewall serves as a gateway between end users and the public network. Hosts connect to the proxy server, which makes a separate connection to the public network. Before transmitting packets to the public network, a proxy server can filter them to enforce network policies. It can also mask the end user’s IP address to protect it from the untrusted network.

Stateful packet inspection

Also called dynamic packet filtering, stateful packet inspection actively monitors the status of connections in a network. By maintaining the status of active connections, these firewalls can, for instance, waive monitoring on incoming traffic if the packet has already been inspected. This way, stateful packet inspectors prevent spoofing and enhance network performance.

Next-generation firewall (NGFW)

A typical NGFW leverages both static packet filtering and stateful inspection and has some features, including deep packet inspection (DPI), to achieve enterprise-wide security. It may also incorporate advanced security features such as network security systems (IDS and IPS), antivirus filtering and malware filtering to enhance security further.

What Are the Benefits of Using Firewalls?

Implementing firewalls can help an organization in the following ways:

Enhance Data Security with Parallels RAS

Virtually all organizations have their IT infrastructures built on top of the transmission control protocol/internet protocol (TCP/IP) networking stack. Unfortunately, network designers conceived TCP/IP for openness and not security. Cybercriminals know that security vulnerabilities abound in any IT infrastructure.

While implementing a perimeter firewall can help you achieve enterprise security, it is not enough. It is only the first step in many strategies involving layered security that can help you achieve enterprise-grade security. Parallels® Remote Application Server (RAS) is one solution, incorporating a layered security approach that can robustly protect corporate resources.

As an all-in-one virtual desktop infrastructure (VDI) provider, Parallels RAS facilitates anywhere and anytime access to corporate resources from any device with data never leaving the datacenter. Besides centralized management of virtual desktops and applications, Parallels RAS also provides the following additional security features that can streamline perimeter firewalls:

Download your Parallels RAS trial today to achieve a foolproof perimeter firewall!