Reference
Glossary
Plain-English definitions of the networking terms we use across the site. Tap a dotted term in any article to see these inline — or browse the lot here.
backbone
The high-capacity, long-haul carriers (often Tier-1 networks) that move traffic between ISPs and across continents — the internet's motorways.
BGP
Border Gateway Protocol — how independent networks announce which destinations they can reach and choose paths between each other. The internet's routing "gossip."
CGNAT
Carrier-Grade NAT — your ISP shares one public IP among many customers to cope with IPv4 scarcity, so your "public" address often isn't really yours.
DHCP
Dynamic Host Configuration Protocol — hands out IP addresses (plus gateway and DNS settings) to devices automatically when they join a network.
ICMP
Internet Control Message Protocol — the internet's built-in messaging system for errors and diagnostics. Ping and traceroute both rely on it (think "Time Exceeded" and "Echo Reply").
ISP
Internet Service Provider — the company that connects you to the internet (your cable, fiber, or DSL provider).
MPLS
Multiprotocol Label Switching — carriers tag packets with labels to switch them quickly across their backbone (and to build private VPNs). Still common in carrier cores; SD-WAN has eroded its enterprise-edge use.
OSI model
A seven-layer map of how networks work, from physical cables (Layer 1) up to the app you use (Layer 7). Engineers use it to pinpoint which layer a problem lives on.
packet capture
Recording raw network packets off the wire (with tools like tcpdump or Wireshark) to see exactly what's being sent — the network engineer's microscope.
QoS
Quality of Service — rules that prioritise time-sensitive traffic (voice, video) over the rest, so latency-sensitive apps stay smooth when the link is busy.
TCP SYN
The opening packet of TCP's three-way handshake — a "shall we talk?" request. Traceroute can use these to slip past firewalls that block ping.
VLAN
Virtual LAN — splits one physical switch or network into separate logical networks, so devices in different VLANs can't talk to each other without a router in between.