NETWORK16 records
Networking Fundamentals
Plain-language technical references for the concepts behind every network: IP addressing, DNS, DHCP, NAT, subnets, gateways, MAC addresses, TCP and UDP.
These records explain the concepts that every port, command and error on this site assumes. Each one starts with a direct definition and goes as deep as the topic needs. Where a calculation is involved, the matching tool is linked from the sidebar.
IP addressing
How addresses, masks, prefixes and gateways fit together.
- CIDR notationPrefix lengths and address blocksCIDR notation writes an IP address followed by a slash and a prefix length, for example 192.168.0.0/24. The…
- Default gatewayThe router that handles traffic leaving your subnetThe default gateway is the router address a device sends packets to when the destination is outside its own…
- IPv4 vs IPv6Address formats, differences and coexistenceIPv4 uses 32-bit addresses written as four decimal numbers (192.0.2.1) and ran out of new space in 2011;…
- localhost and 127.0.0.1The loopback address127.0.0.1 is the IPv4 loopback address: traffic sent to it never leaves the computer and is delivered back…
- MAC addressHardware addresses on the local linkA MAC address is the 48-bit hardware identifier of a network interface, written as six hex pairs such as…
- Public vs private IP addressesRFC 1918 ranges and what they meanA private IP address comes from the ranges reserved in RFC 1918 (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16)…
- Static vs dynamic IP addressesWhen to fix an address and when to let DHCP assign itA dynamic IP address is assigned automatically by a DHCP server and may change over time; a static IP…
- Subnet maskHow a mask splits network from hostA subnet mask is a 32-bit value that tells a device which part of an IPv4 address identifies the network and…
Core network services
The protocols that make a network usable: names, addresses, translation.
- ARPAddress Resolution ProtocolARP (Address Resolution Protocol) finds the MAC address that belongs to an IPv4 address on the local…
- DHCPDynamic Host Configuration ProtocolDHCP (Dynamic Host Configuration Protocol) is the service that automatically gives a device its IP address,…
- DNSDomain Name SystemDNS (Domain Name System) is the distributed directory that translates human-readable names such as…
- DNS propagationWhy DNS changes take time to appear"DNS propagation" is the period after a DNS record changes during which some resolvers still serve the old…
- NATNetwork Address TranslationNAT (Network Address Translation) lets a router rewrite the private source addresses of outgoing packets to…
Transport & ports
TCP, UDP and the port-number system that sits on top of IP.
- Ephemeral portsClient-side source ports and the dynamic rangeEphemeral ports are the temporary source ports an operating system picks for the client side of each…
- Port number rangesWell-known, registered and dynamic portsPort numbers run from 0 to 65535 and IANA divides them into three ranges: system or well-known ports 0–1023…
- TCP vs UDPReliable streams versus lightweight datagramsTCP delivers a reliable, ordered byte stream over a connection established with a three-way handshake,…