IPv4 Private Address Space and Filtering

According to standards set forth in Internet Engineering Task Force (IETF) document RFC-1918, the following IPv4 address ranges are reserved by the IANA for private internets, and are not publicly routable on the global internet:

• 10.0.0.0/8 IP addresses: 10.0.0.0 – 10.255.255.255
• 172.16.0.0/12 IP addresses: 172.16.0.0 – 172.31.255.255
• 192.168.0.0/16 IP addresses: 192.168.0.0 – 192.168.255.255

Note that only a portion of the “172” and the “192” address ranges are designated for private use. The remaining addresses are considered “public,” and thus are routable on the global Internet.

Use caution when setting filters to exclude these private address ranges. In some cases, Regional Internet Registries (RIRs) have issued adjacent address space to their customers and that space is in use on the global Internet.

In August 2012, ARIN began allocating “172” address space to internet service, wireless, and content providers. There have been reports from the community that many network operators are denying access to devices having IP addresses from within the entire 172 /8 range. As a result, any device with a 172.x.x.x IP address may have difficulty reaching some sites on the global Internet. The only way to solve this problem is for those operators to reconfigure their routers or firewall access controls and filter only address space from the 172.16.0.0/12 range.