Chapter 3 “Configuring and Managing the DHCP Server Role”

Thursday, February 14, 2013

  DHCP is the role Windows Server 2008 uses to manage IP addresses.  DHCP functions at the application layer of the Open System Interconnection (OSI) reference model.  The key aspect of DHCP is that it‘s dynamic, meaning  the network is configured to assign IP addresses to any devices connected to the network.  The different message types that DHCP uses to communicate between a client and a server are, DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, DHCPDECLINE, DHCPACK, DHCPNACK, DHCPRELEASE, and DHCPINFORM.  The first of four messages that are used for the initial lease process are DHCPDISCOVER, which is the first message the client sends looking for a DHCP server.  The second message used is DHCPOFFER, which is when the DHCP server receives the DHCPDISCOVER message and replies with a message that contains IP address information for the client.  The third message is DHCPREQUEST, which is the client letting the server know that it will use the IP information supplied by the DHCP server.  The fourth and last message in the initial lease process is DHCPACK, which is the DHCP server acknowledging the client and assigning the IP address information.  The four step process is easier to remember by using the acronym DORA, for DISCOVER, OFFER, REQUEST, and ACK.  DHCP uses scopes to determine which IP addresses are allocated to client computers.  Administrators can create one or more scopes, however, caution must be taken so multiple DHCP servers are not using the same IP addresses.  Windows server 2008 supports automatic or manual backups.  Backing up the database is very important for fault tolerance in case of a DHCP server failure.