Need to Know

Port 20/21

FTP (File Transfer Protocol) — transfers files between client and server, 20 is data, 21 is control. Unencrypted.

Port 22

SSH (Secure Shell) — encrypted remote terminal access. Also handles SFTP and SCP file transfers.

Port 23

Telnet — unencrypted remote terminal access. Considered insecure, replaced by SSH.

Port 25

SMTP (Simple Mail Transfer Protocol) — sends email between mail servers.

Port 53

DNS (Domain Name System) — translates domain names to IP addresses. Uses UDP for lookups, TCP for zone transfers.

Port 67/68

DHCP (Dynamic Host Configuration Protocol) — 67 is server, 68 is client. Automatically assigns IP, subnet mask, gateway, and DNS.

Port 80

HTTP (Hypertext Transfer Protocol) — unencrypted web traffic.

Port 110

POP3 (Post Office Protocol 3) — downloads email to client and deletes it from the server.

Port 143

IMAP (Internet Mail Access Protocol) — reads email from server, keeps it there, syncs across multiple devices.

Port 137-139

NetBIOS/NetBT — older Windows name resolution and file sharing over a network. Largely replaced by DNS and SMB.

Port 389

LDAP (Lightweight Directory Access Protocol) — used to query and manage directory services like Active Directory.

Port 443

HTTPS (Hypertext Transfer Protocol Secure) — encrypted web traffic using TLS/SSL.

Port 445

SMB/CIFS (Server Message Block/Common Internet File System) — Windows file sharing and printer sharing across a network.

Port 3389

RDP (Remote Desktop Protocol) — remote desktop access to Windows machines. Should be behind a firewall or VPN.

TCP (Transmission Control Protocol)

connection-oriented, establishes a connection before sending data via three-way handshake, guarantees delivery, slower but reliable. Used by HTTP, HTTPS, FTP, SSH, SMTP, RDP.

UDP (User Datagram Protocol)

connectionless, sends data without establishing a connection, no guaranteed delivery, faster but unreliable. Used by DNS, DHCP, streaming, VoIP, gaming.

2.4 GHz

longer range, better at penetrating walls, slower speeds, more congested. Only 3 non-overlapping channels — 1, 6, and 11.

5 GHz

shorter range, faster speeds, less congested, more non-overlapping channels available.

6 GHz

newest band used by Wi-Fi 6E only. Fastest speeds, least congested, shortest range.

Channel width

wider channels (80MHz, 160MHz) mean faster speeds but more interference. Narrower channels (20MHz, 40MHz) are more stable in crowded environments.

Channel selection

choose non-overlapping channels to avoid interference. On 2.4 GHz use only channels 1, 6, or 11.

Regulations

channel availability is regulated by country. Not all channels are legal in all regions.

802.11a

5 GHz, up to 54 Mbps, short range, older standard.

802.11b

2.4 GHz, up to 11 Mbps, long range, slow, congested band.

802.11g

2.4 GHz, up to 54 Mbps, backward compatible with 802.11b.

802.11n

(Wi-Fi 4) 2.4 / 5 GHz dual-band, up to 600 Mbps, introduced MIMO.

802.11ac

(Wi-Fi 5) 5 GHz only, up to 3.5 Gbps, introduced MU-MIMO and beamforming.

802.11ax

(Wi-Fi 6 or 6E) 2.4 / 5 / 6 GHz, up to 9.6 Gbps, best in dense environments, uses OFDMA.

Bluetooth

short range personal area network, typically up to 10 meters. Used for peripherals, headsets, and phones.

NFC (Near Field Communication)

very short range communication of a few centimeters. Used for contactless payments, pairing devices, and access badges.

RFID (Radio-Frequency Identification)

uses radio waves to identify tagged objects. Used in inventory tracking, key fobs, and access cards. Longer range than NFC.

DNS server

resolves domain names to IP addresses for the network.

DHCP server

automatically assigns IP addresses to devices on the network.

File share server

stores and shares files across the network.

Print server

manages printers and print jobs across the network.

Mail server

sends, receives, and stores email.

Syslog server

collects and stores log files from network devices for monitoring and troubleshooting.

Web server

hosts websites and web applications. Examples: Apache, IIS.

AAA server (Authentication, Authorization, Accounting)

controls who can access the network, what they can do, and logs what they did. Example: RADIUS.

Database server

stores and manages databases for applications.

NTP server (Network Time Protocol)

syncs time across all devices on the network. Critical for logging and authentication.

Spam gateway

filters incoming email for spam and malware before it reaches users.

UTM (Unified Threat Management)

all-in-one security appliance combining firewall, antivirus, spam filter, VPN, and intrusion detection.

Load balancer

distributes incoming network traffic across multiple servers to prevent any one server from being overwhelmed.

Proxy server

sits between users and the internet, filters requests, caches content, and can anonymize traffic.

SCADA (Supervisory Control and Data Acquisition)

industrial control systems used to monitor and control physical equipment like power grids and water treatment. Often run older OS and are difficult to patch.

IoT devices

internet-connected devices like smart thermostats, cameras, and sensors. Often have weak security and limited update support.

A record

maps a domain name to an IPv4 address.

AAAA record

maps a domain name to an IPv6 address.

CNAME (Canonical Name)

alias that points one domain name to another. Example: www.site.com points to site.com.

MX record (Mail Exchanger)

tells email where to be delivered, points to the mail server for a domain.

TXT record

stores text information in DNS. Used for spam management and domain verification.

DKIM (DomainKeys Identified Mail)

adds a digital signature to outgoing email so receiving servers can verify it came from a legitimate source.

SPF (Sender Policy Framework)

lists which mail servers are authorized to send email for a domain. Prevents spoofing.

DMARC (Domain-based Message Authentication, Reporting, and Conformance)

policy that tells receiving servers what to do if SPF or DKIM checks fail. Options are reject, quarantine, or allow.

DHCP lease

temporary assignment of an IP address to a device for a set period of time.

DHCP reservation

permanently assigns the same IP address to a specific device based on its MAC address.

DHCP scope

the range of IP addresses the DHCP server is allowed to hand out.

DHCP exclusion

IP addresses within the scope that the DHCP server will never assign. Reserved for static devices like servers and printers.

VLAN (Virtual LAN)

logically segments a network into separate networks even though devices share the same physical switch. Improves security and reduces broadcast traffic.

VPN (Virtual Private Network)

creates an encrypted tunnel over the internet allowing remote users to securely connect to a private network as if they were on-site.

Router

connects different networks together and routes traffic between them. Operates at Layer 3. Handles NAT and DHCP in home networks.

Managed switch

switch with configuration options. Supports VLANs, QoS, and port monitoring. Used in enterprise environments.

Unmanaged switch

plug and play, no configuration needed. Used in home and small office environments.

Access point (WAP)

connects wireless devices to a wired network. Not the same as a router.

Patch panel

central termination point for network cables in a rack. Cables from wall jacks terminate here, then patch cables connect to the switch.

Firewall

monitors and filters incoming and outgoing network traffic based on security rules. Can be hardware or software.

PoE (Power over Ethernet)

delivers electrical power over an ethernet cable to devices like access points, IP cameras, and VoIP phones.

PoE injector

adds power to a single ethernet cable without needing a PoE switch.

PoE switch

switch with built-in PoE on all or some ports.

802.3af

PoE standard, up to 15.4W per port.

802.3at (PoE+)

PoE standard, up to 30W per port.

802.3bt (PoE++)

PoE standard, up to 100W per port.

Cable modem

connects to the internet via coaxial cable from the ISP. Converts cable signal to ethernet.

DSL (Digital Subscriber Line)

internet delivered over existing telephone lines. Slower than cable or fiber.

ONT (Optical Network Terminal)

converts fiber optic signal from the ISP to ethernet for home or office use. Required for fiber internet.

NIC (Network Interface Card)

hardware that connects a device to a network. Each NIC has a unique MAC address burned in at the factory.

MAC address

unique hardware identifier assigned to every NIC. Format is 6 pairs of hex characters. Used for Layer 2 communication.

IPv4 private addresses

10.0.0.0–10.255.255.255, 172.16.0.0–172.31.255.255, 192.168.0.0–192.168.255.255. Not routable on the public internet.

IPv4 public addresses

assigned by ISPs, routable on the internet, unique worldwide.

IPv6

128-bit addresses written in hexadecimal. Virtually unlimited addresses. No broadcast, uses multicast instead.

APIPA

169.254.0.1–169.254.255.254. Automatically assigned when DHCP fails. Seeing this address means DHCP is broken.

Static IP

manually assigned IP address that never changes. Used for servers, printers, and network devices.

Dynamic IP

IP address assigned by DHCP that can change over time. Used for most client devices.

Subnet mask

defines which portion of an IP address is the network vs the host. Example: 255.255.255.0 means the first 3 octets are the network.

Gateway

the IP address of the router. All traffic destined outside the local network is sent here first.

Satellite

internet via satellite dish. High latency, available anywhere including rural areas.

Fiber

fastest internet connection type, uses light through fiber optic cable. Very low latency.

Cable

internet over coaxial cable. Fast, widely available, bandwidth shared with neighbors.

DSL

internet over telephone lines. Slower than cable or fiber but widely available.

Cellular

internet over mobile network (4G LTE, 5G). Portable but can have data caps and variable speeds.

WISP (Wireless Internet Service Provider)

internet delivered via radio signals from a tower. Used in rural areas without cable or fiber.

LAN (Local Area Network)

network within a single building or small area.

WAN (Wide Area Network)

network spanning large geographic areas. The internet is the largest WAN.

PAN (Personal Area Network)

very short range network around a person. Example: Bluetooth connecting a phone to a headset.

MAN (Metropolitan Area Network)

network spanning a city or campus. Larger than LAN, smaller than WAN.

SAN (Storage Area Network)

high-speed network dedicated to storage devices. Used in data centers.

WLAN (Wireless Local Area Network)

LAN using wireless instead of wired connections. A home Wi-Fi network is a WLAN.

Crimper

tool used to attach RJ45 connectors to the end of ethernet cables.

Cable stripper

removes the outer jacket of a cable to expose the inner wires for termination.