Network

IPv6 Cheat Sheet

IPv6 address types, special prefixes and prefix sizes on one page – a quick reference for planning and troubleshooting.

Address types

Prefix	Type	What it’s for
`2000::/3`	Global unicast	Public, routable addresses – what ISPs hand out.
`fc00::/7 (fd00::/8 in use)`	Unique local (ULA)	Private addressing inside a site, like 10.0.0.0/8. Pick a random /48 under fd00::/8.
`fe80::/10`	Link-local	Auto-configured on every interface; valid on one link only. Routers advertise from these.
`ff00::/8`	Multicast	One-to-many. IPv6 has no broadcast – ff02::1 reaches all nodes on the link.
`::1/128`	Loopback	The host itself, like 127.0.0.1.
`::/128`	Unspecified	No address yet (used as a source during DAD) – like 0.0.0.0.
`::ffff:0:0/96`	IPv4-mapped	Represents an IPv4 address in dual-stack sockets, e.g. ::ffff:192.0.2.1.
`64:ff9b::/96`	NAT64	Well-known prefix for translating to IPv4 (DNS64/NAT64).
`2001:db8::/32 · 3fff::/20`	Documentation	For examples and books only – never routed.
`2002::/16`	6to4	Legacy transition tunnels – deprecated.

Prefix sizes in practice

Prefix	Used for	Contains
`/32`	Typical RIR allocation to an ISP	65,536 × /48
`/48`	A business site (RIPE-690)	65,536 × /64
`/56`	A home or small office	256 × /64
`/60`	Minimum some ISPs give homes	16 × /64
`/64`	One LAN / VLAN – required for SLAAC	18.4 quintillion addresses
`/127`	Point-to-point router link (RFC 6164)	2 addresses
`/128`	A single host (loopbacks, host routes)	1 address

Well-known multicast groups

Address	Group
`ff02::1`	All nodes on the link
`ff02::2`	All routers on the link
`ff02::5 / ff02::6`	OSPFv3 routers / designated routers
`ff02::9`	RIPng routers
`ff02::1:2`	All DHCPv6 servers and relays
`ff02::1:ff00:0/104`	Solicited-node (neighbour discovery)
`ff02::fb`	mDNS

Writing addresses (RFC 5952)

8 groups of 4 hex digits: 2001:0db8:0000:0000:0000:ff00:0042:8329
Drop leading zeros: 2001:db8:0:0:0:ff00:42:8329
Replace the longest zero run with :: once: 2001:db8::ff00:42:8329
Lower-case hex; in URLs use brackets: https://[2001:db8::1]:8443/

Handy commands

Linux: ip -6 addr · ip -6 route · ping -6 ipv6.google.com
Windows: ipconfig · netsh interface ipv6 show address · Test-NetConnection -ComputerName ipv6.google.com
Neighbours: ip -6 neigh (Linux) · Get-NetNeighbor -AddressFamily IPv6 (Windows)
Path: traceroute -6 / tracert -6

A one-page reference for the IPv6 facts you look up most: which prefixes mean what, the prefix sizes used in real deployments, the multicast groups you’ll see in packet captures, how to write addresses correctly, and the commands to check them on Linux and Windows.

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