r or acquisition. Think about how long it takes to put an IP address, subnet mask, and default gateway on a server. Not long at all when you're installing the server. Now think about what is involved when the IP address, subnet mask, or default gateway needs to be changed. The server must be taken offline, which usually involves a change control. In many environments, the change needs to happen during a change-control window, which may involve you coming into the office or data center at 2:00 a.m. Now imagine that your company has 100, 200, or 1,000 servers. Don't forget that DNS and/or WINS and Active Directory will need to be updated, too. IP network design is not a glamorous project. It is not something that the CTO will pat you on the back for in a meeting. IP network design is not something that many people will appreciate at all, until it is explained to them. Still, careful planning and design are required to create an IP schema that will allow growth for years to come. Public Versus Private IP Space If you've taken any certification exams, you should be familiar with the idea of public versus private IP space. In a nutshell, there are a select number of IP networks that should not be routed on the public Internet. These networks are described in RFC 1918 ("Address Allocation for Private Internets") as follows: 3. Private Address Space The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets: 10.0.0.0 - 10.255.255.255 (10/8 prefix) 172.16.0.0 - 172.31.255.255 (172.16/12 prefix) 192.168.0.0 - 192.168.255.255 (192.168/16 prefix) A quick note about these ranges is in order. First, the 172.16.0.0 network is not just the /16 range, and it is not the 172.0.0.0/8 range. The range allocated for 172.16.0.0 is a /12. The IP range included in this private range is 172.16.0.0-172.31.255.255. The ranges 172.0.0.0-172.15.255.255 and 172.32.0.0-172.255.255.255 are not composed of private addresses and should not be used as such. This is a common 