IP Address Space

The IPv4 and IPv6 address space can be divided into different address types and sub-types. In this article, we elaborate on the different types that are most commonly used in networking.
Global Network Nodes Illustration

Reserved Addresses

The Internet Assigned Numbers Authority (IANA) reserves some prefixes for special use. For example, all private addresses used in home LANs are reserved addresses. Reserved addresses should not be used on the public Internet (ISPs generally drop packets routing to these "Martian networks").

IPv4 CIDRIPv6 CIDRDescription
0.0.0.0/8Used for Broadcast in a segment
10.0.0.0/8fc00::/7Used as Private address
127.0.0.0/8::1/128Used for loopback address (localhost)
169.254.0.0/16fe80::/10Used as link-local address
192.0.2.0/242001:db8::/32Used for documentation
224.0.0.0/4ff00::/8Used for Global multicast
255.255.255.255/32Used for Broadcast

Private Addresses

Private addresses are part of the reserved space and used in most LAN networks. IPv4 private subnets were defined by RFC1918, and the IPv6 private prefix was defined by RFC4193. Networks using private addresses rely on Network Address Translation (NAT) to route traffic to the global internet.

CIDRDescription
10.0.0.0/8Class A Private address
172.16.0.0/12Class B Private address
192.168.0.0/16Class C Private address
fc00::/7IPv6 unique local address (ULA)

Link Local Address

Link-local addresses are used by devices to auto-configure their own IP address without DHCP. In IPv6, link-local addresses are mandatory and widely used for routing protocol adjacencies.

  • 169.254.0.0/16: IPv4 link-local address (APIPA).
  • fe80::/10: IPv6 link-local address.

Global Addresses (Public Space)

Global or public IP addresses are unique addresses used by all devices connected to the Internet. They are distributed by the five Regional Internet Registries (RIR): AFRINIC, APNIC, ARIN, LACNIC, and RIPE.

PA and PI Addresses

  • Provider Aggregatable (PA): Addresses allocated by an ISP to an end user. The ISP aggregates these PA addresses and advertises the larger subnet via BGP.
  • Provider Independent (PI): Addresses allocated directly by the RIR to the end user. This allows an Autonomous System (AS) to advertise the prefix via BGP to multiple ISPs (Multihoming) and switch providers without changing IPs.