Internet Protocol version 6 (IPv6) is the successor to IPv4, designed to solve IPv4 address exhaustion with a 128-bit address space (340 undecillion addresses). Unlike IPv4's 32-bit addresses, IPv6 fundamentally redesigns packet headers for efficiency, mandates IPsec support, and integrates autoconfiguration directly into the protocol through Stateless Address Autoconfiguration (SLAAC) and Neighbor Discovery Protocol (NDP). Understanding IPv6 is critical for modern networking: address representation rules differ significantly from IPv4, with hexadecimal notation, compression rules, and prefix-based subnetting replacing traditional subnet masks. The most important concept to internalize is that every interface always has multiple addresses simultaneously—link-local for local communication, global unicast for internet routing, and often temporary privacy addresses—all coexisting on the same interface.
What This Cheat Sheet Covers
This topic spans 15 focused tables and 122 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
Table 1: Address Format and Representation
Reading and writing IPv6 addresses correctly is the first hurdle for anyone coming from IPv4. These notations are all valid ways to write the same 128 bits — the compression rules (dropping leading zeros, collapsing runs of zeros to ::) exist purely to make the long hexadecimal strings manageable, while the bracket and zone-ID forms handle the edge cases that trip people up in URLs and on link-local interfaces.
| Format | Example | Description |
|---|---|---|
2001:0db8:0000:0042:0000:8a2e:0370:7334 | • 128 bits divided into eight 16-bit hextets separated by colons • each hextet written as 4 hexadecimal digits (0-9, a-f). | |
2001:db8:0:42:0:8a2e:370:7334 | • Leading zeros within each hextet can be omitted • 0042 becomes 42, but at least one digit must remain per hextet | |
2001:db8::8a2e:370:7334 | • Consecutive all-zero hextets replaced with :: to shorten address• :: may appear only once per address to avoid ambiguity | |
2001:db8::/32fe80::/10 | • Slash notation indicates network prefix length in bits (similar to IPv4 CIDR) • replaces subnet mask concept entirely in IPv6. |