Dynamic Host Configuration Protocol
DHCP is a protocol that allows client computers to startup and automatically receives an IP address, subnet mask, default gateway, DNS Server address, WINS address. The DHCP Server provides a client with an IP address in three steps.
1. The client boots and broadcasts a DHCP IP request to all nodes on the local network.
2. A DHCP server on the local network receives the request and prepares to distribute an IP address to the client in the form of a DHCP IP address lease.
3. After the DHCP Server has determined the right prerequisites information from the client, it issues the client with a DHCP IP address lease.
With the DHCP IP address lease, there is an important piece of information delivered, the lease duration. This informs the client how long the IP address can be used before the client must check back with the DHCP server to renew the lease or get a new lease. The DHCP client caches this information, and when the lease duration is nearly up or when the system is restarted or the network is reinitialized, the DHCP client contacts the DHCP server to ensure the lease can still be used so that it can be renewed or replaced with a new lease.
Automatic Private IP Addressing
Automatic Private IP Addressing is a feature of Windows clients and servers that allows systems on the same network to automatically establish network connectivity and communication with one another when no DHCP server is available. The IP addresses automatically assigned to adapters with this configuration are in the 169.254.0.0/16 subnet range.
DHCP Relay Agents
When a DHCP client broadcasts a DHCP client broadcast, that broadcast is normally only allowed on the local network, which means that if there is no local DHCP server, there is no DHCP server response. The role of a DHCP relay agent is to pick up the local DHCP client broadcast and to forward that request to a designated DHCP server on a remote network.
Before a DHCP server can be useful, it must be authorized, and a scope must be created and activated. DHCP authorization can be performed using the DHCP Post-Install Wizard or it can be performed from within the DHCP server console.
In Windows Server 2012 there is a new feature called DHCP Failover. Here two DHCP Servers can be configured to provide leases form the same pool of addresses.The servers then replicate lease information between them, which enables one server to assume responsibility for providing leases to all clients on the subnet when the other server is unavailable.
There are two configuration choices:
Load-Sharing mode (default): Leases are issued from both servers equally.
Hot-standby mode: Leases are issued from the primary server until it fails whereupon the lease data is automatically replicated to the secondary server which assumes the load. Limitations: 1. Only supports maximum of two server 2. Limited to IPv4 scopes and subnets