A+ Core 1 High-yield

SSH (Secure Shell)

Port 22 TCP | Encrypted CLI remote terminal

Telnet

Port 23 TCP | Unencrypted CLI remote terminal

RDP (Remote Desktop Protocol)

Port 3389 TCP | Windows GUI remote desktop

FTP (File Transfer Protocol)

Ports 20/21 TCP | File transfer (20 Data, 21 Control)

SMB (Server Message Block)

Port 445 TCP | Modern Windows file & printer sharing

HTTP vs HTTPS

HTTP = Port 80 TCP (Unencrypted) | HTTPS = Port 443 TCP (Encrypted)

SMTP

Port 25 TCP | Outgoing email sending between servers

POP3 vs IMAP

POP3 (110 TCP) = Single device download | IMAP (143 TCP) = Multi-device sync

DNS

Port 53 TCP/UDP | Resolves domain names to IP addresses

DHCP

Ports 67/68 UDP | Auto-assigns IP configurations (67 server, 68 client)

NetBIOS / NetBT

Ports 137-139 TCP/UDP | Legacy Windows local network name resolution & sessions

SNMP

Ports 161/162 UDP | Network device monitoring (161 queries, 162 traps)

LDAP

Port 389 TCP/UDP | Active Directory user credential lookup

APIPA Range

169.254.0.1 to 169.254.255.254 | Auto-assigned when DHCP server is unreachable

Private IPv4 Ranges

Class A: 10.x.x.x | Class B: 172.16.x.x-172.31.x.x | Class C: 192.168.x.x

Loopback IPv4 Address

127.0.0.1 | Tests local network stack hardware functionality

Laser Printer - Ghosting

EP Drum or dirty wiper blade retaining residual charge

Laser Printer - Smudging / Toner Rubs Off

Fuser Assembly failure (insufficient heat or pressure)

Laser Printer - Vertical Black Lines

Scratched EP drum

Laser Printing 7-Step Process Order

Processing -> Charging -> Exposing -> Developing -> Transferring -> Fusing -> Cleaning

Inkjet Printer - Streaks or Missing Lines

Clogged printhead nozzles (run head cleaning utility)

Thermal Printer - Blank Pages

Thermal paper loaded upside down

Print Queue Stuck / Nothing Printing

Restart Windows Print Spooler service (spoolsv.exe)

Garbled / Junk Text Print Output

Incorrect or corrupted print driver installed

Printer Console Test Page vs OS Test Page

Console test = Local hardware only | OS test = Driver, spooler, and network path

6-Step Troubleshooting Methodology Sequence

1. Identify problem -> 2. Establish theory -> 3. Test theory -> 4. Plan/Implement -> 5. Verify system -> 6. Document findings

Port Forwarding (Port Mapping)

Routes incoming external port traffic to a specific internal private IP address

Static IP vs DHCP Reservation

Static = Typed on client device | Reservation = Binds MAC address to IP inside router

Single-Mode Fiber (SMF) vs Multimode Fiber (MMF)

SMF = Narrow core, Laser, Long distance (Yellow) | MMF = Wide core, LED, Short distance (Orange/Aqua)

RAID 0 / 1 / 5 / 10 Specs

RAID 0 = Striping | RAID 1 = Mirroring | RAID 5 = Parity (Min 3) | RAID 10 = Striped Mirrors (Min 4)