Networking Fundamentals · beginner · ~10 min
Read IPv4 and IPv6 addresses and tell public, private, and special ranges apart.
IPv4 = 32 bits, four octets (192.168.1.10). IPv6 = 128 bits of hex. Private ranges (10/8, 172.16/12, 192.168/16) aren't internet-routable; 127.0.0.1 / ::1 are loopback.
Recon starts with "what's in scope and what's reachable?" Public addresses are directly attackable; private ones need a foothold first. Recognising loopback and link-local keeps you from wasting time — or straying out of scope.
Octet range. Each IPv4 octet is 0–255 (8 bits). RFC 1918 private ranges. 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. Loopback. 127.0.0.1 / ::1 — the host itself. IPv6 compression. :: replaces one run of all-zero groups, once per address.
An IP address identifies a host on a network at the Internet layer.
32 bits, written as four dotted decimals: 192.168.1.10. Each octet is 0–255, so there are ~4.3 billion addresses — not enough, which is why NAT and IPv6 exist.
Not routable on the public internet; used inside homes and offices:
10.0.0.0/8172.16.0.0/12192.168.0.0/16127.0.0.1 — loopback (this machine). All the labs in this course target loopback.0.0.0.0 — "any/unspecified".169.254.0.0/16 — link-local (DHCP failed).128 bits, written as eight groups of hex: 2001:0db8:85a3::8a2e:0370:7334. Double-colon :: compresses one run of zero groups. Loopback is ::1. Link-local addresses start fe80::.
A public IP is globally routable and assigned by an ISP/registry. A private IP only works inside a local network and must be translated (NAT) to reach the internet. During recon, knowing whether an address is public or private tells you whether it's directly reachable.
IPv4 is 32 bits in dotted decimal; IPv6 is 128 bits in hex. Private ranges and loopback aren't publicly routable. Telling public from private is the first reachability question in recon.