IPv6
the Internet Protocol, version 6IPv6 is IPv4’s successor, built to never run out of addresses. It gives every host a 128-bit address, configures itself with no DHCP server, and restores end-to-end connectivity without NAT — the same job as IPv4, with room to spare.
IPv6 is IPv4 with a vastly bigger address space and no need for NAT.
How it works
Eight groups of four hex digits. Runs of zeros collapse to ::, so this shortens to 2001:db8:85a3::8a2e:370:7334.
No header checksum, no router fragmentation, optional features moved into extension headers — so routers do less work per packet than with IPv4.
What IPv6 does, step by step
A host learns the network prefix from a router advertisement and builds its own address — SLAAC, no DHCP needed.
128-bit source and destination — enough that every device on earth can have a public address.
Routers forward by prefix, dropping the Hop Limit each step — the same idea as IPv4’s TTL.
Options like fragmentation or IPsec live in chained extension headers, keeping the base header lean.
In cybersecurity
IPv6 fixes some IPv4 problems and adds its own: a huge space that’s hard to scan, but public addresses that expose hosts directly.
A /64 holds 18 quintillion addresses, so brute-force host discovery is effectively impossible.
Hosts are globally reachable, so a real firewall — not NAT — must do the shielding.
Neighbour Discovery replaces ARP and inherits similar on-link spoofing risks; RA Guard helps.
Random interface IDs stop a stable address from tracking a device across networks.
Running IPv4 and IPv6 together doubles the policy to get right — an easy place to leave a hole.
Long or crafted header chains can slip past filters that don’t parse them fully.