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DHCP Deployment Design Goal: Allocating IP Addresses

Updated: November 10, 2008

Applies To: Windows Server 2008

DHCP enables the allocation of IP addresses to client computers and other devices in enterprise environments. If you look at your installed base of TCP/IP devices, you can roughly separate them into three categories:

  • Network devices: These include routers, firewalls, and switches.

  • Servers: Computers that provide services to other computers.

  • Clients: Computers that consume services provided by the servers.

Each of these devices needs an IP address to be fully functional. However, the method for allocating addresses to these devices can differ, depending on the category of the device.

The most widely deployed version of Internet Protocol (IP) is IP version 4, which defines an addressing scheme based on 32-bit addresses. Each address includes a network/subnet address component and an individual host address component; therefore, there are practical limitations to the numbers of addresses available. If all IP devices were required to have a globally unique IP address, the available pool of addresses would have run out long ago. Class C IP addresses, for example, have 24 bits reserved for network ID, which means that there are approximately 16 million network IDs available. This might seem like a lot of IDs, but each of them can have only 254 possible hosts on it (because there are only 8 bits left for host IDs).

Given the limitations of providing globally unique IP addresses, most enterprise networks use private IP addressing within the organization. The private IP address space is defined as three sets of IP addresses set aside by the Internet Assigned Numbers Authority (IANA) and is specified in RFC 1918. The reserved IP ranges are:

  • 10.0.0.1 through 10.255.255.254

  • 172.16.0.1 through 172.31.255.254

  • 192.168.0.1 through 192.168.255.254

Private addressing schemes are typically used in conjunction with technologies such as network address translation (NAT), which allows hosts with private addresses to access external services through proxy devices. NAT works by temporarily allocating a real registered address for the duration of a given session only.

If you need to use registered IP addresses for public devices, it is crucial that you do not waste addresses on unused hosts. However, even if you are using private addressing within the organization, your addressing scheme might require you to reuse addresses where possible. For this reason, an IP address allocation and management solution is required.

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