Network penetration testing is the security assessment of an organisation's network infrastructure: the firewalls, routers, switches, servers, and services that connect systems to each other and to the internet. It is distinct from web application penetration testing, which focuses on the application layer, though the two often overlap where applications are hosted on infrastructure that is also in scope.
Most organisations need both. A web application with no exploitable vulnerabilities sitting on a network with misconfigured segmentation, default credentials on network devices, or unpatched services gives attackers a path to the application from the inside regardless of application-layer security.
This guide covers what network penetration testing includes, how each phase is conducted, what findings look like, and how to evaluate whether a network pentest scope covers the surfaces that matter for your environment.
Network penetration testing splits into two primary scope types that require different access, different methodology, and produce different findings.
External network penetration testing simulates an attacker operating from the internet with no prior access to the organisation's network. The tester has only what is publicly visible: IP ranges, domain names, publicly exposed services, and any information discoverable through open-source intelligence gathering.
What external testing covers:
The goal: demonstrate whether an attacker with no inside access could gain a foothold in the network. The most impactful external finding is an exploitable vulnerability that allows code execution or authentication bypass on a perimeter system, because that converts external access to internal access. Many engagements find less dramatic but still significant issues: exposed management services, outdated SSL/TLS versions, services running with default credentials, or information disclosure that enables more targeted attacks.
Internal network penetration testing simulates an attacker who is already inside the network perimeter, either through a successful external breach, a malicious insider, a compromised third-party device, or physical access. The tester operates from a position on the internal network, often starting with a standard user account.
What internal testing covers:
The goal: demonstrate what an attacker who has gained any internal access could reach and do. Internal penetration testing consistently produces higher-severity findings than external testing at most organisations because internal environments receive less security attention than the external perimeter.
A structured network penetration test follows a consistent set of phases regardless of whether it is external, internal, or both.
For external testing, reconnaissance begins before any direct contact with the target network. Testers gather information through open-source intelligence (OSINT): DNS records, WHOIS data, public certificate transparency logs that reveal subdomain structure, job postings that reveal technology stacks, LinkedIn profiles of employees that reveal security tooling, and threat intelligence sources.
This phase maps the full attack surface before any active scanning begins. A well-conducted reconnaissance phase often reveals systems and services that the organisation did not include in the scope because they were unaware they existed: forgotten subdomains, legacy systems, development environments exposed to the internet.
With reconnaissance complete, testers conduct systematic scanning of the target IP ranges using tools like Nmap to identify:
For internal testing, this phase also maps the internal network topology: which subnets exist, what routing exists between them, what network devices control traffic between segments.
The output of this phase is a comprehensive inventory of the attack surface: every reachable system, every service, every potential vulnerability to investigate.
With the attack surface mapped, testers identify potential vulnerabilities in each discovered service:
Automated vulnerability scanners are used as a starting point in this phase, but they capture only what signature libraries cover. Service-specific and environment-specific vulnerabilities require manual investigation.
The exploitation phase converts vulnerability identifications into confirmed findings. A finding is not reported until exploitation is demonstrated: the tester executed a payload against the vulnerable service, gained access, extracted data, or performed a privileged action.
Common exploitation findings in network penetration testing include:
Once initial access is achieved, testers demonstrate the full impact of the breach. Post-exploitation covers:
This phase answers the business-level question: if an attacker got in here, what could they actually do?
When network segmentation is used to isolate sensitive systems from general network access, the penetration test should specifically validate whether that segmentation actually holds. Segmentation testing attempts to cross defined network boundaries from a position on one side:
This testing is required by PCI DSS every six months when segmentation is used to reduce CDE scope. PCI DSS penetration testing requirements explained covers the specific Requirement 11.4.3 obligation in detail. Segmentation that is assumed but not tested is not security: it is a documented policy with an unknown gap between intent and implementation.
Understanding the boundaries of network penetration testing is as important as understanding what it covers.
Application-layer vulnerabilities in hosted services are typically out of scope for a network penetration test. If a web application is running on a server in scope, the network test confirms that the server is reachable and identifies server-level vulnerabilities. It does not test the application for SQL injection, business logic flaws, or authentication bypass. What a real web application penetration test should cover covers the twelve dimensions that application-layer testing requires separately.
Cloud infrastructure is a different scope from traditional on-premises network testing. Cloud environments have their own security model: IAM configurations, storage bucket access controls, virtual network segmentation, and serverless function security, requiring cloud-specific methodology and tooling.
Business logic and workflow vulnerabilities are outside network penetration testing scope. These require application-layer understanding that network-level assessment does not provide. The security gaps that standard testing misses covers the ten categories most consistently absent from network-focused assessments.
Network penetration testers use a combination of purpose-built tools across each phase. The quality of a network pentest is determined by the tester's judgment in applying and interpreting these tools, not by which tools are used.
Reconnaissance: Shodan, Censys, theHarvester, Maltego, Amass, Recon-ng
Scanning and enumeration: Nmap, Masscan, Netcat, Metasploit's auxiliary scanners, Nessus (for vulnerability correlation, not as a substitute for manual testing)
Exploitation: Metasploit, Impacket (for Windows/Active Directory exploitation), custom exploit code for specific CVEs, Responder (for credential harvesting in internal networks), BloodHound (for Active Directory attack path mapping)
Post-exploitation: Mimikatz (for credential extraction), CrackMapExec (for lateral movement), Empire, Cobalt Strike
Segmentation testing: custom traffic generation tools, Scapy for packet crafting, firewall rule verification tools
The presence of these tools in a vendor's methodology is not a quality signal. Every serious network penetration tester uses some version of this toolset. Quality is determined by what the tester does with these tools and how they document what they find.
A network penetration test report should contain specific findings with exploitation evidence, not a list of scan results. What's in a penetration testing report: a buyer's breakdown covers the full report structure, but for network-specific findings, look for:
Specific proof of exploitation: not "CVE-2024-XXXX was detected on host 10.0.0.5" but "we executed code on host 10.0.0.5 using CVE-2024-XXXX, as demonstrated by the command output in Appendix A."
Lateral movement paths documented: when internal testing is in scope, findings should show the path from initial access to each escalated position, demonstrating how an attacker would actually move through the environment.
Business impact statements: "this vulnerability allows an attacker to access the domain controller, from which all Active Directory credentials can be extracted" is more actionable than "this vulnerability has a CVSS score of 9.8."
Remediation guidance specific to the environment: patch the specific CVE, change specific default credentials, implement specific firewall rules between named segments.
Traditional network penetration testing is periodic: annual or quarterly, with additional testing following significant infrastructure changes. Like web application testing, the gap between annual assessments leaves a window during which new vulnerabilities are introduced but not tested.
Continuous penetration testing and how it differs from annual pentests covers the operational model. For network infrastructure specifically, the most significant change driver is cloud adoption: organisations migrating infrastructure to cloud environments add new network services, change segmentation boundaries, and introduce new IAM configurations on timelines that quarterly network penetration testing cannot match.
Agentic pentesting and continuous security validation covers how continuous agentic testing operates as the always-on security validation layer. How autonomous pentesting works in a DevSecOps pipeline covers the integration model that makes deployment-triggered testing operational without manual engagement scheduling.
For penetration testing services in the US, the 10x Pentest platform provides coverage across application and infrastructure surfaces. See pricing for network penetration testing options or get in touch to discuss scoping a network assessment alongside application coverage for your environment. For VAPT services and PTaaS that include both network and application layers in a continuous coverage model, both pages cover the delivery options.
Q1. What is network penetration testing?
Network penetration testing is a structured security assessment of an organisation's network infrastructure, covering the devices, services, and connectivity that make up the network perimeter and internal network environment. It tests whether an attacker could gain unauthorised access to network systems, move laterally through the network once inside, escalate privileges to administrative control, or reach sensitive systems through paths that are supposed to be restricted. Network penetration testing is distinct from web application penetration testing, which focuses on application-layer vulnerabilities in software rather than network-layer vulnerabilities in infrastructure and services.
Q2. What is the difference between external and internal network penetration testing?
External network penetration testing simulates an attacker operating from the internet with no prior network access. It tests the internet-facing perimeter: publicly exposed services, firewall configuration, VPN gateways, and remote access infrastructure. Internal network penetration testing simulates an attacker who is already inside the network, either through a prior breach or as a malicious insider. It tests network segmentation, lateral movement paths, Active Directory configuration, internal service security, and how far an attacker could reach from an initial internal foothold. Most thorough network assessments include both, because the external test answers "can an attacker get in?" and the internal test answers "once inside, how much damage can they do?"
Q3. How long does a network penetration test take?
A network penetration test for a mid-size organisation typically takes one to two weeks of active testing plus report writing. The duration scales with the number of hosts in scope, the complexity of the internal network topology, and whether the engagement includes Active Directory exploitation, cloud infrastructure, and segmentation testing or focuses on the external perimeter only. Larger enterprise environments with multiple office locations, complex cloud hybrid infrastructure, and extensive internal segmentation can take three to four weeks.
Q4. How often should network penetration testing be done?
At minimum annually, with additional testing following significant network changes: cloud migrations, new office locations or network extensions, firewall rule changes, new remote access infrastructure, or significant changes to Active Directory. PCI DSS requires segmentation testing every six months when segmentation is used to reduce cardholder data environment scope, which affects organisations handling payment card data. For organisations with rapidly evolving infrastructure, continuous network monitoring and periodic targeted penetration testing of changed segments is more appropriate than a fixed annual schedule.
Q5. What is network segmentation testing in a penetration test?
Network segmentation testing specifically validates that network segmentation controls (VLANs, firewalls, access control lists) actually prevent traffic from crossing defined boundaries. It tests whether a system in one network zone can reach systems in another zone that it should not be able to reach. PCI DSS Requirement 11.4.3 mandates segmentation testing every six months when segmentation is used to reduce the scope of the cardholder data environment, because untested segmentation is not effective segmentation for compliance purposes. Segmentation testing should demonstrate from active exploitation attempts that the boundaries are enforced, not merely document that the configuration intends to enforce them.
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