Knowledge material · ~6 min read

System Owner · Learner

Networking and security stop being jargon.

Overview

System Owners speak protocol. You stop saying 'the internet is down' and start saying 'DNS (Domain Name System) resolution is failing for external zones.' Learn the OSI (Open Systems Interconnection) layers, how DNS and DHCP (Dynamic Host Configuration Protocol) actually work, and the Security+ vocabulary your senior techs use casually. Once these click, every incident becomes a layer to test, not a black box.

OSI in working order

▸L1 Physical — cable, light, radio.
▸L2 Data Link — MAC (Media Access Control), switches, VLANs.
▸L3 Network — IP (Internet Protocol), routing, ICMP (Internet Control Message Protocol).
▸L4 Transport — TCP (Transmission Control Protocol)/UDP (User Datagram Protocol) ports.
▸L5–7 Session/Presentation/Application — TLS (Transport Layer Security), HTTP (Hypertext Transfer Protocol), SMB (Server Message Block), DNS.
▸Troubleshoot bottom-up: link light → IP → ping → port → app.

DNS in one breath

DNS resolves names to IPs. A record = name→IPv4, AAAA = name→IPv6, CNAME (Canonical Name record) = alias, MX (Mail Exchange record) = mail, TXT = SPF (Sender Policy Framework)/DKIM (DomainKeys Identified Mail)/verification. TTL (Time To Live) controls cache. Most 'site won't load' tickets are DNS or certificate, not network.

DHCP + subnetting cheat

▸DHCP DORA: Discover → Offer → Request → Ack.
▸/24 = 256 addresses (254 usable). /23 = 512. /25 = 128.
▸Reservations for printers/servers; scopes for users.
▸Conflicts mean two DHCP servers or a static IP inside the scope.

Security+ vocabulary

▸CIA (Confidentiality, Integrity, Availability) triad: Confidentiality, Integrity, Availability.
▸AAA: Authentication, Authorization, Accounting.
▸Threat / Vulnerability / Risk = bad actor / weakness / likelihood × impact.
▸Defense in depth — never trust one control.

Glossary

MAC address: L2 hardware address — unique per NIC (Network Interface Card).
Default gateway: Router IP a host uses for off-subnet traffic.
TTL: Time to live — DNS cache lifetime / IP hop counter.
TLS: Encrypts data in transit; cert chain must be trusted.

Common pitfalls

✗Trusting nslookup over dig — nslookup hides errors.
✗Flat /24 everywhere — kills broadcast domains at scale.
✗Calling 'DNS issue' before checking the cert and the proxy.

Practice drills

▸Trace a packet from your laptop to lovable.dev with traceroute.
▸Build a /27 subnet plan for a 25-person office.