Network Penetration Testing Explained: External vs Internal

External testing evaluates everything reachable from the public internet: firewalls, VPN gateways, exposed services, and email infrastructure. The goal is to determine what an anonymous attacker on the internet could reach and exploit without any prior access.

Internal testing simulates an attacker who has already gained a foothold, whether through a phishing email or a compromised device, and evaluates how far they could move laterally, what privileges they could escalate to, and what critical systems they could ultimately reach.

Most organizations start with an external assessment since it reflects the most likely initial attack path, then follow with internal testing to understand the potential blast radius of a successful breach.