IPv6 Address Types & Key Prefixes

Complete guide to IPv6 address types including unicast, multicast, anycast, and special-use prefixes.

IPv6 Address Categories

IPv6 addresses are organized into three main categories: - **Unicast**: One-to-one communication (most common) - **Multicast**: One-to-many communication - **Anycast**: One-to-nearest communication Unlike IPv4, IPv6 has no broadcast addresses. Multicast handles broadcast-like functions.

Unicast Address Types

Global Unicast
Prefix: 2000::/3
Range: 2000:: to 3fff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
Description: Internet-routable addresses, like IPv4 public addresses
Usage: Public websites, servers, internet-facing devices
Example: 2001:db8:85a3::8a2e:370:7334
Unique Local (ULA)
Prefix: fc00::/7
Range: fc00:: to fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
Description: Private addresses for local networks, like IPv4 RFC 1918
Usage: Internal networks, VPNs, private communication
Example: fd12:3456:789a::1
Link-Local
Prefix: fe80::/10
Range: fe80:: to febf:ffff:ffff:ffff:ffff:ffff:ffff:ffff
Description: Auto-configured on every interface, not routed beyond local link
Usage: Neighbor discovery, router advertisements, local communication
Example: fe80::1%eth0

Special Addresses

AddressNameDescriptionUsage
::1/128LoopbackIPv6 equivalent of 127.0.0.1Testing, local services
::/128UnspecifiedIPv6 equivalent of 0.0.0.0Default route, uninitialized addresses
::/0Default RouteMatches all addressesDefault gateway route
::ffff:0:0/96IPv4-MappedIPv4 addresses mapped into IPv6 spaceDual-stack applications, IPv4 compatibility

Multicast Address Scopes

All multicast addresses start with ff. The second byte indicates scope:

All Scope
Prefix: ff00::/8
Description: All multicast addresses start with ff
Interface-Local Scope
Prefix: ff01::/16
Description: Multicast within single interface
Common Addresses:
ff01::1 - All nodes (interface-local)
Link-Local Scope
Prefix: ff02::/16
Description: Multicast within local network segment
Common Addresses:
ff02::1 - All nodes (link-local)
ff02::2 - All routers (link-local)
ff02::5 - OSPFv3 routers
ff02::6 - OSPFv3 designated routers
Site-Local Scope
Prefix: ff05::/16
Description: Multicast within entire site/organization
Common Addresses:
ff05::2 - All routers (site-local)
Global Scope
Prefix: ff0e::/16
Description: Internet-wide multicast
Common Addresses:
ff0e::1 - All nodes (global)

Anycast Addresses

Anycast addresses look identical to unicast addresses but are assigned to multiple devices. Traffic goes to the "nearest" device with that address. There's no special prefix for anycast - they use the same ranges as unicast addresses.

Example
2001:db8::1 could be anycast if assigned to multiple servers

Common Anycast Uses

  • DNS root servers (multiple servers, same IP)
  • Content delivery networks (CDNs)
  • Load balancing across geographic locations
  • Subnet router anycast (all routers on a subnet)

Reserved Address Ranges

PrefixPurpose
0000::/8Reserved (includes ::1 and IPv4-mapped)
0100::/8Reserved
0200::/7Reserved
0400::/6Reserved
0800::/5Reserved
1000::/4Reserved
4000::/3Reserved
6000::/3Reserved
8000::/3Reserved
a000::/3Reserved
c000::/3Reserved
e000::/4Reserved
f000::/5Reserved
f800::/6Reserved
fc00::/7Unique Local Addresses
fe00::/9Reserved
fe80::/10Link-Local Addresses
fec0::/10Reserved (deprecated site-local)
ff00::/8Multicast

Quick Recognition Tips

Remember These Patterns
Most public IPv6 addresses start with 2 or 3
If you see fe80::, it's link-local (not routed)
If you see fd or fc, it's unique local (private)
If you see ff, it's multicast
::1 is IPv6 loopback (like 127.0.0.1)
:: means all zeros (like 0.0.0.0)