A Note on IPv6

In brief

Why IPv6 exists, how to recognise an IPv6 address, and the blind spot it creates for IPv4-only tools.

Objectives

Recognise an IPv6 address
Explain why IPv6 was needed
Name the IPv6 blind-spot risk

IPv4 has about 4 billion addresses, and we ran out. IPv6 is the replacement: 128 bits, written as eight groups of hexadecimal, like 2001:db8::1. The number of addresses is effectively unlimited.

You do not need to master IPv6 yet, but you must recognise it — it is already carrying a large share of real traffic, and security tools that only watch IPv4 have a blind spot.

Defence

A firewall rule set written only for IPv4 quietly leaves IPv6 wide open. Whenever you harden a host, check both address families.

Recap

IPv6 is 128 bits, written in hex groups
It exists because IPv4 ran out
IPv4-only rules leave IPv6 exposed