Computer Networks and Security
What this domain tests
Computer Networks and Security tests layered communication, addressing, and defensive reasoning. Expect OSI/TCP-IP layers, IP subnetting, TCP versus UDP, ports, DNS/HTTP/TLS, and the CIA triad.
Core rules and concepts
- Layers: application, transport, network, data link, physical. Each layer serves the one above and uses the one below.
- TCP is connection-oriented, ordered, and reliable; UDP is connectionless with no delivery guarantee, used for DNS queries, streaming, and VoIP.
- Private IPv4 ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16; they are not routed on the public internet.
- Symmetric encryption is fast but needs key distribution; asymmetric encryption solves distribution but is slower; hashing provides integrity, not confidentiality.
- HTTPS is HTTP over TLS, default port 443; HTTP is 80. A firewall filters traffic by rules; authentication proves identity, authorization grants access.
Worked example
For 192.168.10.0/26, the mask is 255.255.255.192. The block size is 256−192=64, so subnets start at .0, .64, .128, .192. Each has 2^(32−26)=64 addresses; usable hosts are 64−2=62 after network and broadcast. The first subnet is 192.168.10.0–192.168.10.63, broadcast .63, usable .1–.62. The /26 leaves 6 host bits, so 2^6−2 is the host count.
Traps that cost marks
Saying a /24 has 256 usable hosts; it has 254. Confusing a hub with a switch. Believing encryption alone guarantees integrity. Using port 443 for plain HTTP. Assuming private addresses are reachable without NAT or routing.