Glossary
Networking terms in one or two plain sentences, with a link to the guide or tool that covers each in depth.
A
- A record
- A DNS record that gives the IPv4 address for a name. DNS Lookup
- AAAA record
- A DNS record that gives the IPv6 address for a name. Pronounced "quad A". DNS Lookup
- ASNAutonomous System Number
- A number that identifies one large network on the internet, such as an internet provider or a cloud company. Networks use these numbers to exchange routes with each other. IP Lookup
C
- CGNATCarrier-grade NAT
- A setup where an internet provider shares one public IPv4 address between many customers. It blocks incoming connections such as port forwarding. What is CGNAT
- CIDRClassless Inter-Domain Routing
- A way to write a block of addresses as a starting address and a prefix length, such as 192.168.1.0/24. The number after the slash says how many leading bits are fixed. Subnet Calculator
- CNAME record
- A DNS record that makes one name an alias for another name. What is DNS
D
- Default gateway
- The address your device sends traffic to when the destination is outside your local network. At home this is your router. How to find your router's IP address
- DHCPDynamic Host Configuration Protocol
- The system a router uses to hand out addresses and network settings to devices automatically when they join.
- DNSDomain Name System
- The service that translates names like example.com into IP addresses. What is DNS
- DNS over HTTPSDoH
- A way to send DNS lookups inside an encrypted HTTPS connection so that others on the network cannot read them. What is DNS
- DNSSEC
- An extension to DNS that adds digital signatures, so a resolver can check that an answer is genuine and unaltered. It does not encrypt lookups.
- Dual stack
- Running IPv4 and IPv6 at the same time on one device or network. IPv4 vs IPv6
- Dynamic IP address
- An address your provider lends you for a period and may replace with a different one later. Most home and mobile connections use these. What is an IP address
F
- Firewall
- Software or hardware that decides which network connections are allowed through. Home routers block unrequested incoming connections by default.
G
- Geolocation
- Estimating where an IP address is used. The result is approximate and usually points to the provider's equipment, not the user. What your IP address reveals
H
- Hostname
- A human-readable name for a device or service on a network, such as mail.example.com.
I
- IANAInternet Assigned Numbers Authority
- The body that manages the global pool of IP addresses, the DNS root, and other shared internet numbering.
- IP address
- A number that identifies a device on a network so that data can be sent to it and replies can find their way back. What is an IP address
- IPv4
- The original version of the Internet Protocol. Addresses are 32 bits, written as four numbers like 203.0.113.42. IPv4 vs IPv6
- IPv6
- The current version of the Internet Protocol. Addresses are 128 bits, written as groups of hexadecimal digits like 2001:db8::1. IPv4 vs IPv6
- ISPInternet service provider
- The company that connects you to the internet and assigns your public IP address.
L
- Link-local address
- An address that only works on the local network segment. In IPv4 these start with 169.254 and usually mean no address was assigned. In IPv6 they start with fe80 and every device has one. Public vs private IP addresses
- Loopback address
- An address a device uses to talk to itself: 127.0.0.1 in IPv4 and ::1 in IPv6.
M
- MAC address
- A hardware identifier for a network adapter, used only within the local network. It is not visible to websites and is different from an IP address.
- MX record
- A DNS record that names the mail servers for a domain. Each has a priority, and the lowest number is tried first. DNS Lookup
N
- NATNetwork Address Translation
- The technique a router uses to let many devices with private addresses share one public address. Public vs private IP addresses
- NS record
- A DNS record that lists the authoritative name servers for a domain.
P
- Packet
- A small unit of data sent across a network. Each one is labeled with the address it came from and the address it is going to.
- Port
- A number from 0 to 65535 that identifies a specific service or connection on a device. Web traffic over HTTPS uses port 443.
- Port forwarding
- A router rule that sends incoming connections on a chosen port to a specific device inside the network. Public vs private IP addresses
- Prefix length
- The number after the slash in CIDR notation. It says how many bits identify the network. A larger number means a smaller block. Subnet Calculator
- Private IP address
- An address from a range reserved for use inside local networks, such as 192.168.1.20. It cannot be reached directly from the internet. Public vs private IP addresses
- Proxy
- A server that relays traffic for an application. The destination sees the proxy's address in place of yours. How to change or hide your IP address
- PTR record
- A DNS record that maps an IP address back to a name. Used for reverse DNS. Reverse DNS
- Public IP address
- An address that is unique across the internet. Your provider assigns one to your connection, and websites see it. Public vs private IP addresses
R
- Resolver
- The DNS server that looks up names on your behalf and caches the answers. By default it is run by your internet provider. What is DNS
- Reverse DNS
- Looking up the name associated with an IP address, the opposite of a normal DNS lookup. Reverse DNS
- RIRRegional Internet Registry
- One of five organizations that distribute IP address blocks within a region of the world.
- Router
- The device that connects your local network to your provider and passes traffic between them. How to find your router's IP address
S
- Static IP address
- An address that stays the same until it is deliberately changed. Used for hosting services and for allow-lists.
- Subnet
- A block of IP addresses that share the same leading bits and belong to one network, such as 192.168.1.0/24. Subnet Calculator
- Subnet mask
- The older way to write a prefix length in IPv4, as four numbers. 255.255.255.0 means the same as /24. Subnet Calculator
T
- TLDTop-level domain
- The last part of a domain name, such as com, org, or uk.
- Tor
- A network that routes traffic through several volunteer-run relays so that no single relay knows both the sender and the destination. How to change or hide your IP address
- TTLTime to live
- In DNS, the number of seconds a record may be cached before it must be looked up again. What is DNS
- TXT record
- A DNS record that holds text. Commonly used to prove domain ownership and to publish email security policies.
U
- User agent
- A line of text your browser sends with each request that names the browser, its version, and your operating system. User Agent viewer
V
- VPNVirtual private network
- An encrypted tunnel between your device and a server. Sites you visit see the server's address in place of yours. How to change or hide your IP address