Define configuration methodologies used by network hosts.
IP Configuration Methodology
Windows automates the process for providing a host IP address by using
DHCP manual assignment,
DHCP dynamic assignment, or
APIPA (Automatic Private IP Addressing) automatic assignment.
Depending upon the type of network device or client in your network,
you can use any of these IP configuration methods.
Some hosts on a network, such as special function servers (WINS and DNS), routers, and NAT devices, require manual configuration of the address, mask, and neighbor or gateway addresses. Server applications that assign IP addresses and resolve names to IP addresses require a fixed IP address, subnet mask, and default gateway. Addresses are usually configured manually for DHCP servers, DNS servers, WINS servers, routers, and non-Microsoft hosts that do not support DHCP.
DHCP Manual Method
A system administrator configures the address for a host in the DHCP database. The address is then issued to the host by using the DHCP. Use the manual configuration method for devices that function primarily as servers in a client/server relationship and require fixed IP addresses. You can also configure other network devices, such as routers, with reserved client addresses as well.
Reversed client addresses work well until you change out the network card of the network device that has the client reservation. Client reservations are based on the Media Access Control (MAC) address which is "burned" into the network card by the NIC manufacturer. When you change network cards on the network device, the MAC address will change for that device and thus invalidate the Client Reservation on the DHCP Server.
Request for IP address: When Windows starts, TCP/IP attempts to find a DHCP server on the attached network to obtain a dynamically assigned IP address.
No IP address returned: In the absence of a DHCP server, the client cannot obtain an IP address
APIPA generates an IP address in the form of 169.254.x.y (where x.y. is a unique identifier on the network that the client generates and a subnet mask of 255.255.0.0.
The client computer will continue to search for a DHCP server by issuing a DHCP Discover message every five minutes.
DHCP leases addresses from a scope defined for each subnet. Use dynamic address allocation if the majority of clients on a network support this method and do not require fixed IP addresses. By setting the lease time to infinite, you can also use DHCP to configure clients with a permanent IP address. Setting the lease time to infinite provides flexibility in allocating permanent addresses where the host is DHCP-enabled. However, be aware that the IP addresses assigned in this fashion are not the only permanent IP configuration parameters that will fail to refresh. One of the great advantages of using a DHCP server is that you can also change important network parameters such as the WINS, DNS, and default gateway addresses for large groups of computers without having to visit each computer or manually deleting their leases. If you set DHCP clients with permanent lease configurations,they may not receive updated TCP/IP networking information without additional administrative cost.
Automatic Private IP Addressing
APIPA allows a computer running Windows 2000 in a small, single-segment network to select an IP address automatically when DHCP is not available.
Click the learning bridge link if you would like to review APIPA. The next lesson wraps-up this module.