Only a portion of the “172” and the “192” address ranges are designated for private use. The remaining addresses are “public,” and routable 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 router or firewall access control and filter only address space from the 172.16.0.0 /12 range.