IPv6 Essentials

Updated

September 4, 2026

IPv6 Essentials

IPv6 is not “IPv4 with longer addresses only.” Foundations need address types, prefix notation, link-local, and enough config to run dual-stack labs.

Learning goals

  • Read compressed IPv6 addresses and /prefix lengths
  • Distinguish link-local, unique local, global unicast
  • Configure a static IPv6 address on Linux
  • Know what Neighbor Discovery replaces (ARP, parts of ICMP discovery)

Why IPv6 in this book

  • Dual-stack labs mirror real networks
  • ND and SLAAC appear in operations
  • Many overlays and DC fabrics are IPv6-capable or IPv6-underlay

You do not need to memorize every transition technology here.

Address format

  • 128 bits, eight hextets, e.g. 2001:db8:1:2:3:4:5:6
  • Compress longest zero run with :: (once)
  • Prefix: 2001:db8:1::/64 (common LAN length is /64)

Documentation prefix: 2001:db8::/32 (use in examples).

Address kinds (must know)

Kind Pattern / notes Role
Link-local fe80::/10 On-link only; required on every interface
Unique local (ULA) fc00::/7 (commonly fd00::/8) Private-like lab space
Global unicast 2000::/3 (in practice) Internet-routable space
Multicast ff00::/8 One-to-many
Loopback ::1 Local host
Unspecified :: “Any” / not set 
ip -6 addr
ip -6 route

Interface identifiers and /64

LAN segments almost always use /64. Host bits can come from:

  • Manual config
  • SLAAC (router advertisements)
  • DHCPv6 (where used)

EUI-64 and privacy extensions exist; labs often set static addresses for clarity.

Linux static example

ip -6 addr add 2001:db8:1::10/64 dev eth1
ip link set eth1 up
ip -6 route add default via 2001:db8:1::1 dev eth1
ping -6 2001:db8:1::1

Neighbor Discovery (preview)

IPv6 uses ND (ICMPv6) instead of ARP:

  • Neighbor Solicitation / Advertisement
  • Router Solicitation / Advertisement

Details: ARP, ND, and Local Resolution.

Dual-stack thinking

Stack Failure isolation
IPv4 works, IPv6 fails v6 route, RA, ND, firewall ip6tables/nft
Prefer AAAA vs A Happy Eyeballs / app order

Test both when dual-stack is in scope:

ping -4 <host>
ping -6 <host>

Checkpoint

Write a dual-stack plan for one LAN: IPv4 /24, IPv6 /64 from 2001:db8:10::/64, gateway ::1 / .1, two hosts.

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