Network Penetration Testing: How It Works

Definition

What is network penetration testing?

Network penetration testing is a controlled, authorised simulation of a cyberattack against your network infrastructure. A certified tester attempts to exploit real vulnerabilities in your routers, firewalls, servers, and endpoints to show what an actual attacker could access, how far they could move, and what damage they could cause.

USD 4.44M is the global average breach cost in 2025 (IBM). Network penetration testing costs a fraction of that. And with the penetration testing market growing at 14.2% CAGR through 2031, testing has moved from a nice-to-have to a baseline discipline.

Scope

What does network penetration testing cover?

Network penetration testing evaluates every component in your infrastructure that an attacker could exploit to gain access, escalate privileges, or move between systems. Scope typically includes:

• Perimeter infrastructure: firewalls, routers, VPN gateways, DMZ segments
• Internal network: switches, servers, workstations, domain controllers, Active Directory
• Remote access systems: VPN endpoints, jump boxes, RDP services, Citrix environments
• Wireless networks: access points, WPA configurations, rogue device detection
• Cloud-connected infrastructure: hybrid connections, cloud-facing network interfaces
• OT and IoT segments where in scope: SCADA, industrial controllers, smart building devices

External vs internal — both are required

Most engagements split into an external scope (attacking internet-facing assets from outside) and an internal scope (testing lateral movement and privilege escalation once an attacker is inside the perimeter). They simulate different attackers, surface different findings and satisfy different compliance scopes — PCI DSS v4.0 explicitly requires both. For the full comparison of threats simulated, techniques, costs and which to run first, see our dedicated guide to internal vs external penetration testing.

Methodology

The 7-step methodology

Professional network penetration testing follows a defined methodology aligned to PTES and NIST SP 800-115. Understanding each phase helps your team prepare, participate effectively, and get full value from the engagement. These seven steps are the network-specific application of the standard engagement lifecycle — see the full 8-phase breakdown for the project view, including the remediation retest that closes the loop.

Step 1: Scoping and rules of engagement

Before any testing begins, your team and the penetration tester define the scope in writing. This includes which IP ranges, network segments, and systems are in scope, which are explicitly out of scope, the test type (black-box, grey-box, or white-box), working hours for active testing, and the escalation path if a Critical vulnerability is discovered during the engagement.

Scoping protects both parties and ensures that testing activity is never mistaken for a real attack.

Step 2: Reconnaissance and open source intelligence

The tester gathers publicly available information about your organisation and infrastructure before touching any live systems. This includes DNS records, WHOIS data, publicly visible IP addresses, SSL certificate transparency logs, employee information from LinkedIn (for social engineering context), technology stack identification, and any data that appears in data breach databases.

This phase mirrors exactly what a real attacker does before launching an attack.

Step 3: Network discovery and enumeration

Using tools such as Nmap, Masscan, and Shodan, the tester maps all live hosts, open ports, running services, and operating system versions across in-scope assets. This produces a complete picture of your attack surface and identifies targets for deeper investigation.

Tool note: Nmap for host discovery and port scanning; Nessus or OpenVAS for automated vulnerability identification; Netcat for service banner grabbing; BloodHound for Active Directory enumeration during internal testing.

Step 4: Vulnerability identification

Automated scanners cross-reference discovered services against the CVE catalogue in the National Vulnerability Database and vendor advisories. Human analysis then removes false positives, adds contextual risk assessment, and identifies vulnerabilities that automated tools miss — including business logic issues, authentication bypasses, and configuration weaknesses that are only visible when viewed by an experienced tester who understands your architecture.

Step 5: Exploitation

The tester actively attempts to exploit identified vulnerabilities under the agreed rules of engagement. Common network exploitation techniques include:

• Credential attacks: password spraying, credential stuffing, pass-the-hash against Windows environments
• Service exploitation: targeting unpatched software vulnerabilities with available public or custom exploits
• Man-in-the-middle attacks: ARP poisoning, DNS spoofing on internal network segments
• VLAN hopping: exploiting misconfigured switch trunk ports to access segregated network segments
• Active Directory attacks: Kerberoasting, AS-REP roasting, DCSync, Pass-the-Ticket

Step 6: Post-exploitation and lateral movement

After gaining initial access, the tester attempts to demonstrate the real-world impact by escalating privileges, moving laterally across the network, accessing sensitive systems, and maintaining persistence. This phase answers the critical question: once an attacker is inside your perimeter, how far can they go?

The answer to that question is what drives the most important remediation decisions that come from the engagement.

Step 7: Reporting and remediation guidance

Every network penetration testing engagement closes with a structured report containing an executive summary in business-risk language and a technical findings section with proof-of-concept evidence, CVSS scores, affected systems, and specific remediation steps for each finding. A retest validates that all critical fixes were correctly applied.

Who needs network penetration testing?

• Any organisation with internet-facing infrastructure — every business with a public IP address
• Compliance-required organisations — PCI DSS Req. 11.4 mandates annual penetration testing
• Companies post-merger or post-acquisition — inherited infrastructure carries unknown risk
• Organisations that have recently migrated to cloud or hybrid environments
• MSPs and IT service providers who manage network infrastructure for multiple clients

Infronest

Conclusion

Managing network penetration testing engagements at scale requires a platform that keeps findings organised, clients separated, and reports audit-ready. Infronest's Security and VAPT module handles engagement creation, finding documentation with CVSS scoring, evidence management, and PDF report generation in one tenant-isolated workspace.

Each client's engagement data is fully isolated. Retests track remediation progress automatically. Every action is timestamped for audit-readiness. Start a 14-day free trial at infronest.com — no credit card required.

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Sources

Every figure and methodology reference in this article comes from the following published standards and reports. We cite them so you can verify the claims rather than take them on trust.

• MarketsandMarkets — Penetration Testing Market 2025–2031
• IBM — Cost of a Data Breach Report 2025
• PTES — Penetration Testing Execution Standard
• NIST SP 800-115 — Technical Guide to Information Security Testing
• PCI Security Standards Council — PCI DSS v4.0 Requirement 11.4