Several ranges of addresses are set aside as private for IPv4:
• 10.0.0.0/8
• 172.16.0.0/12
These addresses are considered bogons by services and therefore not routable on the public internet. You can use these addresses to build any kind of network that will not be connected to the global internet (unless the connection is through network address translation, described in a later section).
There is no explicit private address space set aside for ipv6; the
ip community generally assumes ipv6 addresses are so readily available that there is no point in using an address that is not globally routable. However, many people use the 2001:db8::/32 address space set aside for documentation and examples to build private networks.
Note
The fc007::/7 IPv6 address space is reserved for unique local addressing (ULA). In some situations, these addresses can be used to build a private network so long as it is a pure IPv6 network. The interaction between IPv4 addresses and IPv6 ULA addresses can be surprising.
Publicly Routable Address Space
Publicly routable addresses are obtained either through a service provider or through a Regional Internet Registry (RIR).
Figure 2-11 illustrates the flow of IP addresses in the global Internet.
Figure 2-11 IP Address Assignment Flow in the Global Internet The Internet Assigned Numbers Authority (IANA), an international nonprofit, controls the distribution of all number
and name resources used on the Internet. One part of IANA’s job is to control the distribution of IP addresses.
IANA can receive requests for address space from the IETF to reserve blocks of addresses, such as the private addresses discussed in the previous section.
IANA can also receive requests for publicly routable address space from a Regional Internet Registry. There are currently five RIRs, each of which assigns addresses within a region:
• The African Network Information Center (AFRINIC) serves
Africa.
• The American Registry for Internet Numbers (ARIN) serves the United States, Canada, parts of the Caribbean, and Antarctica.
• The Asia-Pacific Network Information Center (APNIC) serves East, South, and Southeast Asia.
• The Latin American and Caribbean Network Information
Center (LACNIC) serves most of the Caribbean and all of Latin America, including South America and North America up to
Mexico.
• The Réseaux IP Européens Network Coordination Centre
(RIPE) serves Europe, Central Asia, and West Asia.
Large organizations can request addresses directly from one of these RIRs; however, it is almost impossible to get IPv4 address space. Most of the RIRs have run out of free IPv4 space.
Organizations can also purchase IPv4 addresses from
specialized resellers.
RIRs are more willing to assign IPv6 addresses to organizations.
Requirements vary by RIR, so it is best to check the RIR for your region to find out how to obtain an IPv6 network address.
Operators and end users can also get addresses from their
service provider when they purchase Internet access; this is the most common way to obtain IP addresses.
