6.1. Key Security Concepts

💡 First Principle: Security is about managing risk, not eliminating it. Every threat exploits a vulnerability using an exploit. Your job is to implement mitigations that reduce risk to an acceptable level. Think of it like home security—you can't prevent all burglaries, but locks, alarms, and lights make your house harder to rob than your neighbor's.

What happens without security awareness: Consider this scenario—a network engineer leaves default credentials on a new router ("admin/admin") and plans to change them later. An automated scanner finds the device within hours. The attacker now has enable access to a core router: they can intercept traffic, redirect it to malicious servers, create backdoor accounts, and pivot to attack internal systems. One "temporary" oversight compromises the entire network.

The security mindset: Think like an attacker. Every service you enable, every port you open, every user account you create is a potential entry point. What could go wrong? How could someone abuse this? That paranoid thinking helps you design more secure systems.

Why network engineers need security knowledge:

• Misconfigured ACLs create holes attackers walk through
• Default credentials on network devices are publicly known
• Unencrypted protocols (telnet, HTTP, SNMPv1/v2c) expose sensitive data
• Physical access to network equipment bypasses all logical controls