Private IP Address (RFC 1918)
Under the present IPv4 addressing scheme, the IP address space is divided into two types: public IP address
space and private IP address space. The public IP address space is routable via the Internet and is managed by
one of the Regional Internet Registries (RIR). A small part of the address range, shown in Table 2-1, has been
set aside and designated as a "reserved" or "private" IP address range, as documented in RFC 1918. These
addresses are reserved for use by private networks and are not routed on the Internet. These private IP address
ranges must be filtered on border routers so that no traffic with a private address as source is allowed from the
Internet. Table 2-3 includes the details of the private address ranges.
Table 2-3. RFC 1918 Address Ranges Reserved for Private Use
Class Range of Addresses
A 10.0.0.0 through 10.255.255.255
B 172.16.0.0 through 172.32.255.255
C 192.168.0.0 through 192.168.255.255
In addition to the previously described RFC 1918-based private addresses range, the IANA has blocked a special
Class B private address range and reserved it for automatic private IP addressing (APIPA). For example, when
using Dynamic Host Configuration Protocol (DHCP), if the DHCP server cannot be found for an assigned IP
address, the operating system will automatically assign addresses from this special block to enable
communication.
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