What Is Network Penetration Testing? Types and Process

Every business assumes its firewall is doing its job, right up until the day it isn’t. A network penetration test is how you find out for certain, on your terms, instead of learning the hard way from an intruder. Instead of guessing whether your defenses hold, you hire an ethical hacker to attack them under controlled conditions and hand you a map of every way in. This guide explains what network penetration testing is, the types you can run, and the step-by-step process a professional test follows, so you know what you are buying and what to expect.

What’s in This Guide

What Network Penetration Testing Is

Network penetration testing, often shortened to pen testing or called ethical hacking, is a security assessment in which authorized experts mimic the tools and techniques of real attackers to break into your network. The goal is not to cause damage. It is to find the weaknesses that matter, prove they can be exploited, and report them so you can close the gaps first.

The practice is grounded in an established government standard. The NIST definition of penetration testing describes it as security testing in which evaluators mimic real-world attacks to identify ways to circumvent the security features of an application, system, or network. That word “mimic” is the whole idea: a pen test is the closest thing to a genuine breach you can experience without the consequences of one.

A simple analogy helps. A penetration test is like hiring a professional burglar to break into your own building while you watch. They pick the locks, climb through the window you forgot about, and then hand you a report showing every way they got in, so you can fix it before a real thief tries. You get all the lessons of a break-in with none of the loss.

It helps to separate a pen test from the two things people confuse it with. It is more than a vulnerability scan, which only produces a list of possible flaws. And it is more than a security audit, which checks your policies and controls against a checklist. A penetration test goes further and asks a harder question: given these weaknesses, can a skilled attacker actually get in, and how much damage can they do once they are there? Answering that question is what makes the results so valuable.

Source: NIST Computer Security Resource Center glossary

The Network Penetration Testing Process

A professional pen test is not a smash-and-grab. It follows a repeatable methodology so the results are thorough, safe, and something you can act on. The most widely used framework comes from the government’s technical guide to security testing, NIST Special Publication 800-115, which organizes a test into four phases.

1. Planning. Before anything is touched, the tester and the business agree on the rules. This phase sets the scope (which systems are in play), the objectives, the timing, and the legal rules of engagement. Getting this right is what separates an authorized test from a crime, and it is where you decide whether the test is external, internal, or both.
2. Discovery. The tester maps the target. This means reconnaissance, gathering public information about the organization, followed by scanning to find live hosts, open ports, running services, and operating system versions. Each finding is then compared against known vulnerabilities to build a list of promising ways in.
3. Attack. This is the heart of the test. The tester attempts to actively and controllably exploit the weaknesses found during discovery. A successful exploit is not the end. From that first foothold the tester tries to escalate privileges, move laterally to other systems, and reach the sensitive data or critical systems that would matter most in a real breach. This proves the true business impact, not just the theoretical risk.
4. Reporting. The test is only as good as the report it produces. The tester documents every vulnerability found, exactly how it was exploited, the evidence, and a risk rating for each. The most important part is a clear, prioritized set of remediation recommendations, so your team knows what to fix first and how.

A strong engagement adds one more step that the standard implies but businesses often skip: retesting. After your team fixes the reported issues, the tester verifies the fixes actually worked. A finding is not truly closed until someone has confirmed the door is locked.

Source: NIST SP 800-115, Technical Guide to Information Security Testing and Assessment

Types of Network Penetration Testing

“Network penetration testing” is really a family of tests. Which one you need depends on what you are worried about: an outsider on the internet, an insider or a laptop that has already been compromised, or both. The tests are described two ways, by where the attack comes from and by how much the tester knows going in.

By attack position: external and internal

The first and most important split is where the tester stands.

• External penetration testing attacks your network from the outside, the way an anonymous internet-based attacker would. It targets everything exposed to the public internet: firewalls, VPN gateways, web servers, email servers, and remote access points. This is the test that answers the question, “Can someone break in from their laptop across the country?” It matters more than ever because attackers are hammering exactly these edge systems, as the data below shows.
• Internal penetration testing starts from inside the network, simulating an attacker who already has a foothold, whether a malicious employee, a contractor, or, most commonly, an outsider who got in through a phished password or an infected device. It measures the damage that intruder could do: how far they can move, what they can reach, and how quickly a small breach becomes a company-wide one. Sound network segmentation is one of the main defenses an internal test puts to the proof.

By tester knowledge: black, gray, and white box

The second dimension is how much information the tester is given before they start. More knowledge means a faster, deeper test; less knowledge means a more realistic simulation of an outside attacker.

Most businesses get the best value from a gray box approach. Giving the tester a little information cuts out the slow guesswork of a pure black box test and lets them spend the budget where it counts, actually exploiting weaknesses rather than just discovering the network exists.

Explore Managed Networking and Security

Penetration Testing vs Vulnerability Scanning

This is the single most common point of confusion, and it costs businesses real money when they buy one thinking they got the other. A vulnerability scan and a penetration test are related, but they are not interchangeable. The short version: a scan finds potential problems automatically, and a pen test proves which of those problems a human attacker can actually use against you.

A vulnerability scan is an automated tool that checks your systems against a database of known flaws and produces a report, often a long one. It is fast, cheap, and worth running frequently. But it has no judgment. It cannot tell you whether a flagged weakness is genuinely exploitable in your environment or a harmless false positive, and it will not chain three small issues together into one serious break-in the way a real attacker does. A penetration test brings the human expert who does exactly that.

The two work best together. Frequent scanning keeps a running inventory of possible weaknesses between tests, and the annual pen test cuts through that list to show which ones truly threaten the business. Scanning is often part of a broader attack surface management program, while the pen test is the periodic deep dive that validates it all.

Why Network Penetration Testing Matters

The business case is simple: attackers are actively exploiting the exact weaknesses a pen test is designed to find, and the cost of them succeeding keeps hitting new records. Testing is how you get ahead of it instead of cleaning up after it.

Start with how criminals are getting in. Verizon’s 2025 Data Breach Investigations Report found that the exploitation of vulnerabilities was an initial way into 20% of breaches, an increase of 34% over the prior year, driven in part by attacks on internet-facing edge devices and VPNs. Those edge systems are precisely what an external penetration test probes first.

Vulnerability exploitation now sits just behind stolen credentials as a leading way attackers break in. Here is how the top initial-access methods stacked up in the same report.

When those attacks land, the bill is steep. IBM’s 2025 Cost of a Data Breach Report put the global average cost of a breach at $4.44 million. In the United States the figure climbed to an all-time high of $10.22 million. For a small or midsize business those numbers translate into downtime, lost customers, and recovery costs that can threaten the company’s survival.

There is a compliance driver too. For any business that handles payment cards, testing is not optional. The PCI Security Standards Council requires, under Requirement 11.4 of PCI DSS, that organizations perform both internal and external penetration testing at least once every 12 months and after any significant change. Similar expectations show up in SOC 2 audits, cyber insurance applications, and the security questionnaires your larger customers send you. A current pen test report is fast becoming table stakes for doing business.

Source: Verizon Data Breach Investigations Report | IBM Cost of a Data Breach Report | PCI Security Standards Council

How to Get Started With a Penetration Test

A penetration test is only worth the money if it is scoped well and the findings actually get fixed. You do not need to understand the technical details, but knowing the shape of a good engagement helps you buy the right one. A sensible path looks like this.

1. Define the goal and scope. Decide what you are testing and why. Is this about your external exposure, your internal risk, a compliance requirement like PCI DSS, or all three? A short conversation about your most sensitive systems and data sets the scope. A cybersecurity risk assessment is a useful first step if you are not sure where your real risk sits.
2. Choose the right type. Match the test to the goal. Most businesses benefit from an external test to check internet-facing exposure and an internal, gray box test to measure how far a foothold could spread.
3. Agree on the rules of engagement. Confirm the timing, the systems in and out of bounds, and how sensitive findings are handled. This keeps the test safe for a live business network.
4. Act on the report and retest. The findings are the whole point. Work through the prioritized fixes, then have the tester verify them. Pair the results with ongoing network security monitoring so new threats are caught between tests.

Few small and midsize businesses have the in-house expertise to run this well, which is why penetration testing is usually delivered by a specialized security team or a managed provider. If you want a broader view of how outsourced security works, our guide to managed security service providers covers the model. For a baseline of the protections every organization should have first, CISA’s cyber guidance for small and midsize businesses is a strong free starting point.

Source: Cybersecurity and Infrastructure Security Agency, small and midsize business resources

Common Questions About Network Penetration Testing

Related Terms

Get a Free Security Audit From CNiC

David McFarlene Founder & CEO

David McFarlene is the owner and founder of CNiC Solutions, a trusted IT services and cybersecurity company serving the Houston, TX area. With over 20 years of experience in managed IT, infrastructure design, cloud solutions, and data security, David helps businesses and homeowners stay protected and productive through dependable, personalized technology support. He leads the CNiC Solutions team with a focus on reliability, transparency, and long-term relationships, ensuring clients always have a knowledgeable expert they can trust.

See Full Bio

IT Services Network Cabling Cloud Solutions Cybersecurity Data Backup & Recovery Managed IT Services Infrastructure Management Telecommunications Virtual CIO (vCIO) WebRTC