Specifications

Chapter 1 Understanding Networking and IP Addressing
Networking using IP
Niagara Release 2.3
Niagara Networking & Connectivity Guide Revised: May 22, 2002
1–23
IP Address Allocation
The organization responsible for ensuring the uniqueness of IP numbers is the
Internet Corporation for Assigned Names and Numbers (ICANN). It delegates the
assignment of the public address space to the Internet Assigned Numbers Authority
(IANA), which then distributes it to three Regional Internet Registries (RIRs),
located throughout the world. These regional authorities then allocate it further to
Local Internet Registries (LIRs). LIRs are also known as Internet service providers
or ISPs, and they commonly hold a number of address ranges to lease to customers.
However, due to the explosion of growth on the Internet, these public addresses are
rapidly being depleted.
Private IP
Addresses
The designers of IP anticipated this problem and set aside three blocks of IP
addresses for use in private networks. This allows organizations to implement IP
addressing without having to apply to an ISP for unique global IP addresses for every
host. Because these addresses are blocked by the global Internet routing system (the
routers will drop packets from these addresses), the address space can simultaneously
be used by many different organizations. However, hosts using these private
addresses cannot be reached directly from the Internet (nor can they communicate to
the Internet).
Table 1-9 lists the sanctioned private addresses for each class.
Network
Address
Translation
(NAT)
To overcome the reachability limitation, the use of private addresses is commonly
teamed with a technique called Network Address Translation (NAT) to provide
access to the Internet by hosts that require it. Typically, some device (such as a router,
firewall, or proxy server) has a supply of legitimate addresses and translates between
a private address and a public one for a host that needs access to or from the Internet.
240.0.0.0 to
247.255.255.255
These addresses are experimental and should never be assigned as a host
address.
10.0.0.0 to
10.255.255.255
172.16.0.0 to
172.31.255.255
192.168.0.0 to
192.168.255.255
See “Private IP Addresses”.
Table 1-8 Special IP addresses.
Table 1-9 Private address ranges.
Class Range Description
A 10.0.0.0 to 10.255.255.255 This provides one network of 16,777,216 hosts.
B 172.16.0.0 to 172.31.255.255 This range provides 16 networks, each with 65,534
hosts.
C 192.168.0.0 to 192.168.255.255 This address range provides 254 networks, each with
254 hosts.