IP Basics

What an IP address is, IPv4 structure, public/private, subnetting

• What Is an IP Address? A Complete Plain-English Guide What an IP address does, how IPv4's 32 bits and dotted-decimal notation work, the network/host split, public vs private, IPv4 vs IPv6, and how to find your own IP on any OS.
• Public vs. Private IP Addresses and NAT Explained The difference between public and private IP addresses, the RFC 1918 ranges, other special ranges, and exactly how NAT and port translation let many devices share one public IP.
• How to Find My IP Address (Public and Private) Find your IP address in seconds. See your public IP at the top of this site, and learn how to find your private IP on Windows, macOS, Linux, iPhone and Android.
• Subnetting and CIDR Basics, with Worked Examples How subnet masks and CIDR notation relate, how to compute the network address, broadcast and host count, how to split a block (VLSM), and how IPv6 prefixes differ.
• Planning CIDR for AWS VPC (and Any Cloud) How to choose VPC and subnet CIDR ranges that avoid overlaps, leave room to grow, and play nicely with peering and VPNs.