Cheat Sheets Networking

IPv6 Address Types Cheat Sheet

IPv6 special prefixes, from ::1 and fe80::/10 to fc00::/7, ff00::/8 and 2001:db8::/32, with multicast groups, notation rules and EUI-64, checked with Python.

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An IPv6 address is 128 bits written as eight groups of four hex digits. Its first bits say what kind of address it is. The ranges below were checked with Python's ipaddress module (first and last address of each block); the examples use the documentation prefix 2001:db8::/32. Check an address's syntax with the IPv6 Address Validator.

Writing IPv6 addresses

Rule Full form Short form
Drop leading zeros in each group 2001:0db8:0000:0000:0000:ff00:0042:8329 2001:db8:0:0:0:ff00:42:8329
Replace one run of zero groups with :: 2001:db8:0:0:0:ff00:42:8329 2001:db8::ff00:42:8329
:: only once, on the longest run (the leftmost if tied) 2001:0db8:0000:0000:0001:0000:0000:0001 2001:db8::1:0:0:1
Lowercase hex (RFC 5952) 2001:DB8::A 2001:db8::a
Brackets in URLs, with the port outside https://[2001:db8::1]:8443/

Convert in either direction with the IPv6 Address Compressor and the IPv6 Address Expander.

Special-purpose prefixes

Prefix Type Range (first to last) Notes
::/128 Unspecified :: "No address yet", used as a source during setup
::1/128 Loopback ::1 Same role as 127.0.0.1
::ffff:0:0/96 IPv4-mapped ::ffff:0.0.0.0 to ::ffff:255.255.255.255 An IPv4 address seen by a dual-stack socket: ::ffff:192.0.2.1
64:ff9b::/96 NAT64 well-known prefix 64:ff9b:: to 64:ff9b::ffff:ffff 192.0.2.1 becomes 64:ff9b::c000:201
64:ff9b:1::/48 Local-use NAT64 For private NAT64 deployments
100::/64 Discard-only Traffic sent here is dropped (blackholing)
2000::/3 Global unicast 2000:: to 3fff:ffff:...:ffff The public internet
2001::/32 Teredo IPv6 tunnelled over UDP/IPv4
2001:db8::/32 Documentation 2001:db8:: to 2001:db8:ffff:...:ffff For examples only; never routed
3fff::/20 Documentation (RFC 9637, 2024) 3fff:: to 3fff:fff:ffff:...:ffff Larger example space
2002::/16 6to4 Deprecated tunnelling; embeds an IPv4 address (2002:c000:201::1 carries 192.0.2.1)
fc00::/7 Unique local (ULA) fc00:: to fdff:ffff:...:ffff Private addressing; in practice only fd00::/8 is used
fe80::/10 Link-local fe80:: to febf:ffff:...:ffff On every interface; never routed; needs a zone: fe80::1%eth0
fec0::/10 Site-local Deprecated since 2004 (RFC 3879)
ff00::/8 Multicast ff00:: to ffff:ffff:...:ffff One-to-many; IPv6 has no broadcast

Create a random private prefix with the IPv6 ULA Generator: a ULA is fd followed by 40 random bits, giving a /48.

Multicast scopes and groups

The fourth hex digit of a multicast address is its scope.

Scope Prefix Reach
1 ff01:: Interface-local (loopback)
2 ff02:: Link-local: the local network segment
5 ff05:: Site-local
8 ff08:: Organisation-local
e ff0e:: Global
Group Members
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::fb mDNS
ff02::16 MLDv2-capable routers
ff02::1:2 All DHCPv6 servers and relay agents on the link
ff05::1:3 All DHCPv6 servers in the site
ff02::1:ff00:0/104 Solicited-node groups used for neighbour discovery

Solicited-node address: ff02::1:ff plus the last 24 bits of the unicast address. For 2001:db8::abcd:1234 it is ff02::1:ffcd:1234.

Common prefix lengths

Prefix Typical holder Contains
/32 ISP or large organisation 65,536 /48s
/48 One site 65,536 /64 subnets
/56 Home connection 256 /64 subnets
/64 One LAN 2^64 = 18,446,744,073,709,551,616 addresses
/127 Point-to-point router link 2 addresses
/128 One host (loopback, a single route) 1 address

Keep LANs at /64: SLAAC and many features expect it. Plan subnets with the IPv6 Subnet Calculator.

Interface identifiers (EUI-64)

SLAAC can build the last 64 bits from the MAC address: split it in half, insert ff:fe, and flip the seventh bit of the first byte.

Step Value
MAC address 00:1a:2b:3c:4d:5e
Insert ff:fe in the middle 00:1a:2b:ff:fe:3c:4d:5e
Flip bit 7 of the first byte (00 → 02) 02:1a:2b:ff:fe:3c:4d:5e
Link-local address fe80::21a:2bff:fe3c:4d5e

Because this exposes the hardware address, modern systems use random or stable-privacy identifiers (RFC 8981, RFC 7217) for global addresses instead.

Try these tools

IPv6 Address Compressor

Compress a full-form IPv6 address to its shortest valid :: representation.

IPv6 Address Expander

Expand a compressed IPv6 address (using ::) to its full 8-group form.

IPv6 Address Validator

Validate an IPv6 address and classify it as global unicast, unique local, link-local, multicast, or loopback.

IPv6 ULA Generator

Generate a random IPv6 Unique Local Address /48 prefix (fdxx:xxxx:xxxx::/48) with its /64 subnets.

IPv6 Subnet Calculator

Professional IPv6 subnet calculator.

See also

  • Glossary IPv6
    IPv6 is the newer version of the Internet Protocol, using 128-bit addresses to replace the nearly exhausted 32-bit IPv4 space.
  • Glossary Unique local address (ULA)
    A unique local address is a private IPv6 address in fc00::/7, used inside a site or between sites but not routed on the public internet.
  • Glossary CIDR
    CIDR (Classless Inter-Domain Routing) is the notation that writes an IP network as an address plus a prefix length, such as 192.168.1.0/24.
  • Cheat sheet CIDR and Subnet Mask Cheat Sheet
    Every IPv4 prefix from /8 to /32 with its subnet mask, wildcard mask, address count and usable hosts.
  • Guide How Subnetting Works
    How an IP address splits into network and host parts, how to find a network and broadcast address.

Frequently Asked Questions

That is normal. Every interface has a link-local fe80:: address, and usually one or more global addresses as well, such as a stable one plus temporary privacy addresses that change regularly for outgoing connections.

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