Q: I've heard that I can now use non-RFC 1918 IP addresses in an Azure virtual network; what does this mean?
A: RFC 1918 specifies IP addresses that are assigned to be used internally (i.e., within an organization) and will not route on the Internet. Specifically, these are:
When you create an Azure virtual network, an IP address range is assigned that's then divided into virtual subnets. The IP address range selected prior to this update required the IP addresses to be from the RFC 1918 range (i.e., non-routable on the Internet). However, numerous customers had very large IP address spaces that were Internet-routable and they wanted to use those addresses in Azure, the same way they use them on-premises. The update to Azure virtual networks announced at TechEd Europe 2014 now allows virtual networks to use non-RFC 1918 IP address ranges. Of course, it's important to use non-RFC 1918 addresses only for IP spaces that you own in your organization. For most organizations, the use of RFC 1918 ranges is still the best option, and non-RFC 1918 use would be on an exception basis.