Networking 101

Jargon Decoder

Search 100+ networking terms explained in plain English — no experience required

Term	Plain-English Definition
Access Port	A switch port that belongs to a single VLAN. Devices connected here don't know anything about VLANs — the switch handles it all. Most end-device ports (PC, phone) are access ports.
ACL (Access Control List)	A list of rules on a router or switch that permit or deny traffic. Think of it as a bouncer's list at the door — if your name is on it, you get in; if not, you're denied.
Address	A unique identifier for a device. MAC addresses are hardware addresses; IP addresses are logical addresses assigned by software/DHCP.
AP / WAP	Access Point or Wireless Access Point — the box on the ceiling that broadcasts Wi-Fi. Connects wireless devices to the wired network.
ARP	Address Resolution Protocol — how a device figures out the MAC address of another device when it only knows the IP address. "Who has 192.168.1.1? Tell me your MAC."
ASN	Autonomous System Number — a unique ID given to organisations that run their own public routing (usually ISPs and big companies using BGP).
Backbone	The high-speed core of a network that carries the bulk of the traffic. Usually fiber-connected switches or routers in the data center.
Bandwidth	The maximum amount of data a link can carry per second (e.g. 1 Gbps). Not the same as speed — it's more like the width of a pipe, not how fast the water flows.
BGP	Border Gateway Protocol — the routing protocol that runs the internet. Used between ISPs and large enterprises to exchange routing information between autonomous systems.
Broadcast	A message sent to all devices on a network at once. Like shouting in a room instead of whispering to one person.
CDP / LLDP	Cisco Discovery Protocol / Link Layer Discovery Protocol — protocols that let network devices announce themselves to their neighbors. Useful for mapping what's connected to what.
CIDR	Classless Inter-Domain Routing — a way to write IP addresses with their prefix length: e.g. 192.168.1.0/24. The /24 tells you how many bits are the network part.
CLI	Command Line Interface — the text-based interface you use to configure routers and switches. No mouse, just typing commands.
Collision Domain	The group of devices that share a single network segment. Old hubs had one big collision domain; switches give each port its own, eliminating most collisions.
Convergence	When all routers in a network agree on the best routes after a change (like a link going down). During convergence, traffic may be temporarily disrupted.
CRC	Cyclic Redundancy Check — a math checksum attached to Ethernet frames so the receiver can detect if bits got corrupted in transit. Bad CRCs usually mean a cable or NIC issue.
CSMA/CD	How old Ethernet shared a cable — devices listen before transmitting and back off if a collision happens. Mostly irrelevant now that switches give each device a full-duplex link.
Default Gateway	The router's IP address on your subnet. When your PC wants to reach something outside its own network, it sends traffic here first. Usually ends in .1 (e.g. 192.168.1.1).
DHCP	Dynamic Host Configuration Protocol — automatically gives IP addresses, subnet masks, gateways, and DNS servers to devices when they join the network. No manual config needed.
DMZ	Demilitarized Zone — a network segment that sits between the internet and your internal network, used for public-facing servers (web, email). Isolated so a compromise doesn't reach internal systems.
DNS	Domain Name System — translates names like google.com into IP addresses. Like a phone book for the internet. Without it you'd need to memorise IPs for every website.
Duplex	Whether a link can send and receive at the same time. Full-duplex = simultaneous send/receive (modern). Half-duplex = only one direction at a time (old hubs). Mismatched duplex causes errors.
EIGRP	Enhanced Interior Gateway Routing Protocol — a Cisco proprietary routing protocol. Faster convergence than RIP, simpler than OSPF. Used inside enterprise networks.
Encapsulation	Wrapping data in headers at each OSI layer as it travels down the stack. Like putting a letter in an envelope, then that envelope in a box, then shipping the box.
Ethernet	The most common wired networking standard. Uses frames with MAC addresses. Runs over copper (Cat5e/6/6a) or fiber cable. Speeds: 100 Mbps, 1 Gbps, 10 Gbps, 25 Gbps, 100 Gbps.
Failover	When a primary link or device fails and traffic automatically switches to a backup. Good network design always has a failover plan.
Firewall	A device (or software) that enforces rules about what traffic is allowed in or out of a network. Can block ports, protocols, or specific IP addresses.
Frame	A Layer 2 packet. Contains source/destination MAC addresses, data payload, and a CRC checksum. Switches work with frames.
Full Mesh	A network topology where every device connects directly to every other device. Very resilient but expensive — connections grow exponentially with device count.
Gateway	Usually refers to the default gateway — the router interface on your subnet that forwards traffic to other networks. Sometimes used for application-layer gateways (API, email).
GRE	Generic Routing Encapsulation — a tunneling protocol that wraps packets inside other packets to carry them over a network that wouldn't normally support them (e.g. non-IP traffic over IP).
HSRP / VRRP	Hot Standby Router Protocol / Virtual Router Redundancy Protocol — protocols that let two routers share a virtual IP as the default gateway. If one fails, the other takes over invisibly.
Hub	Old networking gear that broadcasts all traffic to every port. Replaced by switches, which are smarter. You'll mostly see hubs in museums now.
ICMP	Internet Control Message Protocol — used by ping and traceroute. It's a diagnostic/control protocol, not for carrying user data. Firewalls often block it, which is why ping sometimes fails.
IDF	Intermediate Distribution Frame — the wiring closet on each floor or wing of a building. Connects to the MDF (main distribution frame) in the data center.
Interface	A physical or logical connection point on a device. A router port, a switch port, or a virtual interface (loopback, VLAN interface) are all interfaces.
IP Address	A unique logical address for a device on a network. IPv4: four numbers 0–255 separated by dots (e.g. 192.168.1.10). IPv6: eight groups of four hex digits (e.g. 2001:db8::1).
IPv4	The most common version of IP addressing — 32-bit addresses written as four decimal numbers (e.g. 10.0.0.1). About 4.3 billion possible addresses.
IPv6	The newer version — 128-bit addresses, allowing a virtually unlimited number. Written in hex groups separated by colons. Slowly replacing IPv4 but both coexist today.
ISP	Internet Service Provider — the company that connects your organisation to the internet. Examples: AT&T, Comcast, Spectrum, Lumen.
Jitter	Variation in the delay of arriving packets. High jitter causes choppy audio/video in VoIP and video conferencing calls.
Jumbo Frames	Ethernet frames larger than the standard 1500-byte MTU, typically 9000 bytes. Used in storage networks (iSCSI, NFS) to reduce overhead. All devices on a path must support them.
LAN	Local Area Network — the private network inside your building or campus. Switches connect devices on the LAN.
Latency	The time it takes a packet to travel from source to destination. Measured in milliseconds (ms). Low latency is good — important for real-time traffic like voice and video.
Layer 2	The Data Link layer of the OSI model — where switches and MAC addresses live. Concerned with getting frames between directly connected devices.
Layer 3	The Network layer of the OSI model — where routers and IP addresses live. Concerned with routing packets between different networks.
Loopback	A virtual interface on a router or switch (e.g. Loopback0) used as a stable management address that is always up as long as the device is running.
MAC Address	Media Access Control address — a hardware address burned into every NIC at the factory. Written as six pairs of hex digits: AA:BB:CC:DD:EE:FF. Switches use these to forward frames locally.
MDF	Main Distribution Frame — the central wiring hub, usually in the data center or main comms room. All IDFs connect back here.
MTU	Maximum Transmission Unit — the largest packet size a link can carry without fragmenting. Standard Ethernet MTU is 1500 bytes.
Multicast	Sending data to a specific group of devices simultaneously (not all, not one). Used for video streaming, IPTV, and routing protocol updates.
NAT	Network Address Translation — rewrites IP addresses on packets as they pass through a router. Most commonly used to let many private IPs share one public IP for internet access.
NIC	Network Interface Card — the hardware in your computer or server that connects to the network. Has a MAC address burned in at the factory.
NTP	Network Time Protocol — keeps all devices on the network synchronised to the same time. Critical for logging, authentication (Kerberos), and certificates.
OSPF	Open Shortest Path First — a popular routing protocol that automatically finds the best paths between networks. Routers share a map of all links and calculate routes using Dijkstra's algorithm.
Packet	A unit of data at Layer 3. Contains source and destination IP addresses plus the data payload. Routers move packets between networks.
PAT	Port Address Translation — a form of NAT where many internal IPs share one public IP by using different source port numbers. Also called NAT overload. Most home routers use this.
Ping	A basic test that sends an ICMP echo request to a device and waits for a reply. If you get replies, the path to that device is working. If not, there's a connectivity issue.
PoE	Power over Ethernet — delivers electrical power alongside data over the same Ethernet cable. Used to power APs, IP phones, cameras, and small switches without a separate power supply.
Port (physical)	The socket on a switch or router where you plug in a cable.
Port (logical)	A number (0–65535) that identifies which application or service traffic belongs to. HTTP = port 80, HTTPS = 443, SSH = 22. The Port Lookup tool lists them all.
Protocol	A set of rules that defines how devices communicate. Like a language — both sides must speak the same protocol to understand each other. Examples: TCP, IP, HTTP, OSPF, SNMP.
QoS	Quality of Service — policies that prioritise certain types of traffic (like voice and video) over others so they don't get delayed by bulk downloads.
RFC 1918	The standard that defines private IP address ranges: 10.x.x.x, 172.16–31.x.x, and 192.168.x.x. These addresses are not routed on the public internet.
RJ-45	The standard 8-pin connector on the end of an Ethernet cable. The plastic tab that breaks off if you're not careful.
Route	A path through the network to reach a destination. Routers store routes in a routing table and choose the best one for each packet.
Router	A Layer 3 device that moves packets between different IP networks. Looks at IP addresses to decide where to forward traffic.
SFP	Small Form-factor Pluggable — a hot-swappable module that goes into a switch or router to provide a specific type of connection (fiber, copper, 1G, 10G, etc.).
SNMP	Simple Network Management Protocol — used by monitoring systems to query and get alerts from routers, switches, and servers. Versions: v1 (insecure), v2c (common), v3 (secure).
Spanning Tree (STP)	A protocol that prevents network loops by blocking redundant paths. Without it, a loop would flood the network with traffic until it crashed.
SSH	Secure Shell — encrypted remote access to the CLI of a router, switch, or server. Replaced Telnet, which sent passwords in plain text.
Subnet	A logical subdivision of an IP network. Devices in the same subnet can communicate directly without going through a router. Splitting a big network into subnets improves security and performance.
Switch	A Layer 2 device that connects devices on the same network. Learns which MAC addresses are on which ports and forwards frames only to the correct port — unlike a hub.
TCP	Transmission Control Protocol — ensures reliable delivery of data. Breaks data into segments, sends them, and retransmits any that are lost. Used by HTTP, SSH, FTP, email.
Telnet	An old, unencrypted remote access protocol. Everything including passwords is sent in plain text. Use SSH instead.
Throughput	The actual amount of useful data transferred per second, after accounting for overhead and errors. Always less than the theoretical bandwidth of the link.
Traceroute	A tool that shows every router (hop) between you and a destination and how long each hop takes. Great for pinpointing where a connection is slow or breaking.
Trunk Port	A switch port that carries traffic for multiple VLANs simultaneously, tagged with 802.1Q headers. Used to connect switches together or connect a switch to a router.
UDP	User Datagram Protocol — fast, connectionless delivery of data. No guarantee of delivery or order. Used where speed matters more than perfection: DNS, VoIP, streaming, gaming.
Unicast	A one-to-one transmission — one source sends to exactly one destination. The most common type of network traffic.
Uplink	A port that connects a device "up" toward the core of the network. E.g. the port on an access switch that connects back to the distribution switch.
VLAN	Virtual LAN — a logical grouping of ports on a switch that behaves as if they were on a separate network. Separates traffic without needing separate physical hardware. E.g. VLAN 10 = Data, VLAN 20 = Voice.
VPN	Virtual Private Network — creates an encrypted tunnel over the internet, making remote devices appear to be on the local network. Examples: IPsec, SSL/TLS, OpenVPN, WireGuard.
VRF	Virtual Routing and Forwarding — multiple independent routing tables on one physical router. Like having separate routers inside one box. Used for network segmentation.
WAN	Wide Area Network — the network beyond your building: internet, MPLS circuits, SD-WAN. Connects your LANs across distances.
Wildcard Mask	The inverse of a subnet mask used in ACLs and OSPF statements. 0 means "must match," 1 means "don't care." e.g. 0.0.0.255 matches any host in a /24 network.

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