Numbering your network

For private TCP/IP networks that are not directly or indirectly connected to the Internet, you can use any range of valid IP addresses from Class A, B, or C.

For private TCP/IP networks that are indirectly connected to the Internet by using a network address translator (NAT) or an application layer gateway such as a proxy server, the Internet Assigned Numbers Authority (IANA) recommends that you use the private IP addresses shown in the following table.

Private network ID	Subnet mask	Range of IP addresses
10.0.0.0	255.0.0.0	10.0.0.1 – 10.255.255.254
172.16.0.0	255.240.0.0	172.16.0.1 – 172.31.255.254
192.168.0.0	255.255.0.0	192.168.0.1 – 192.168.255.254

Numbers in these ranges are reserved by IANA for private use on TCP/IP networks and are not used on the Internet.

Usually, for security reasons, you should not connect more than a few TCP/IP systems within your network directly to the Internet. For any host systems on your network that connect to the Internet, you must obtain the use of registered IP addresses from your Internet service provider (ISP).

Notes

If your ISP cannot provide sufficient public addresses to accommodate your needs and you are located in the United States, you can apply directly to the American Registry for Internet Numbers (ARIN) to obtain an IANA-assigned IP network address. For more information about registering a public address, see the American Registry for Internet Numbers Web site.
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For more information about private IP address numbering for private networks, see RFC 1918, "Address Allocation for Private Internets."