An IPv4 network is defined by a combination of an IPv4 network number plus a network mask, or netmask. An IPv6 network is defined by its site prefix, and its subnet prefix, if subnets are used.
To enable the private network to communicate to external networks in the Internet, you must obtain a registered IP number for your network from the appropriate organization. This address becomes the network number for your IPv4 addressing scheme or the site prefix for your IPv6 addressing scheme.
ISPs provide IP addresses for networks with pricing that is based on different levels of service. Investigate with various ISPs to determine which provides the best service for your network. ISPs typically offer dynamically allocated addresses or static IP addresses to businesses. Some ISPs offer both IPv4 and IPv6 addresses.
If your site is an ISP, you obtain IP address blocks for your customers from the Internet Registry (IR) for your locale. IANA is ultimately responsible for delegating registered IP addresses to IRs around the world. Each IR has registration information and templates for the locale that the IR services. For information about the IANA and its IRs, refer to the IANA's IP Address Service page.