Network penetration testing evaluates the security of your network infrastructure — the servers, firewalls, switches, and services that underpin your operations. It's distinct from application testing and addresses a different layer of the attack surface.
External Network Penetration Testing
An external network penetration test evaluates what an attacker could achieve from outside your network perimeter — typically from the internet. The tester maps your external attack surface (public IP addresses, exposed services, DNS records), identifies vulnerabilities in internet-facing systems, and attempts to breach the perimeter.
**What it covers:** Exposed services and ports, firewall and edge device configurations, VPN gateway security, mail server security, DNS security, SSL/TLS configuration, and any internet-facing management interfaces.
**What it reveals:** Whether an external attacker could breach your perimeter, and how far they could get. It tests your first line of defence.
Internal Network Penetration Testing
An internal network penetration test evaluates what an attacker could achieve once inside your network — simulating a compromised employee device, a phished user, or an attacker who has breached the perimeter. This is where the most damaging real-world attacks occur, because internal networks are typically far less hardened than external perimeters.
**What it covers:** Network segmentation, Active Directory security, internal service vulnerabilities, lateral movement paths, privilege escalation opportunities, credential harvesting, access to sensitive data and systems, and the effectiveness of detection and monitoring controls.
**What it reveals:** How far an attacker could move laterally once inside, what sensitive systems and data they could reach, and whether your internal defences detect and contain the activity.
Why Both Matter
Most organisations invest heavily in perimeter security but underinvest in internal network hardening. This creates a "hard exterior, soft interior" problem — once the perimeter is breached (through phishing, a compromised credential, or a supply-chain attack), the attacker faces little resistance. External testing validates the perimeter; internal testing reveals whether your defences hold once that perimeter is bypassed.
How Simuna Infosec Approaches Network Testing
We conduct both external and internal network penetration testing as part of our comprehensive security assessment capability. Our network testing covers the full attack path — from perimeter breach through lateral movement to data access — and identifies the specific segmentation gaps, misconfigurations, and privilege-escalation paths that real attackers exploit.