Network Security Concepts and Fundamentals
The CIA Triad and Its Companions
Start with confidentiality, integrity, and availability, then extend to authentication, authorization, accounting (AAA), non-repudiation, and defense in depth. Questions often test which property a control protects: encryption at rest protects confidentiality; hashing protects integrity; redundancy protects availability; digital signatures provide integrity plus non-repudiation. A common trap is assigning a single control to multiple properties loosely - be precise about the primary property.
Core Vocabulary
Know the difference between a vulnerability (a weakness), a threat (a potential actor or event), a risk (likelihood times impact), and an exploit (the mechanism that abuses a vulnerability). Understand identification vs. authentication vs. authorization, and least privilege vs. separation of duties. Familiarize yourself with security models (Bell-LaPadula for confidentiality, Biba for integrity) and cryptographic primitives (symmetric vs. asymmetric, hashing, key exchange, certificates/PKI).
Protocols and Layers
Map controls to the OSI/TCP-IP layers: TLS for transport confidentiality, IPsec for network-layer tunnels, SSH for management, DNSSEC for name resolution integrity. Know port numbers and default behaviors for TLS, IPsec (AH/ESP), and common management protocols.
Worked Example / Rule of Thumb
When a stem asks which control best mitigates a risk, first name the property at stake, then pick the control that directly enforces it at the right layer. Example: to prevent credential theft on an untrusted network, the answer is a TLS-encrypted session, not a stronger password policy alone - the latter reduces but does not address interception.
Trap to watch: 'strongest' vs. 'most appropriate.' Exams often want the control that fits the layer and threat, not the theoretically strongest one.