Windows Master DHCP server configuration

The primary role of a DHCP server is to assign a dynamic IP address to a network client. These assigned IP addresses are reserved by the DHCP server as a set of addresses consisting of multiple addresses, and they are typically a contiguous address (except for certain addresses that are excluded when the administrator configures the DHCP server). When a network client requests a temporary IP address, the DHCP server looks at the address database to assign a client an IP address that is still not in use. This section provides readers with some information about DHCP services and how to configure a DHCP server under Windows Server.

What is a DHCP service

In early network management, assigning IP addresses to network clients is a complex task for network administrators. Assigning an IP address is a very complex task for a larger network because each client computer must have a separate IP address to avoid a duplicate IP address and cause a network conflict.

To solve this problem, the generation of DHCP service is caused. DHCP is the acronym for Dynamic Host Configuration protocol, which is a communication protocol used in the TCP/IP communication protocol to temporarily specify a machine's IP address. You must have a DHCP server on the network when you use DHCP, while other computers perform DHCP clients. When a DHCP client sends a broadcast message asking for a dynamic IP address, the DHCP server provides an available IP address and subnet mask to the client based on the currently configured address. In this way, the network administrator does not have to set the IP address for each client computer one at a time, the DHCP server automatically assigns IP addresses to the Internet computer, and the client computer only applies the IP address to the DHCP server when it is powered on, and returns it immediately after completion.

Using a DHCP server to dynamically assign IP addresses not only saves network administrators from assigning IP addresses, but also ensures that assigned addresses are not duplicated. In addition, the IP address of the client computer is allocated when it is needed, thus increasing the usage of the IP address. To learn more about the role of DHCP, let's look at how it works.

There are usually three ways DHCP assigns IP addresses, the first is a fixed IP address, each computer has its own fixed IP address, this address is fixed, suitable for each workstation in the area network address, unless the network architecture changes, otherwise these addresses can usually be used forever. The second is dynamic allocation, where the DHCP server gives an IP address whenever the computer needs to access network resources, but when the computer leaves the network, the IP address is released and available for use by other workstations. The third type is assigned by the network manager in a manual manner. If DHCP is used with a WINS server, the mapping relationship between the computer name and the IP address can be handled automatically by the WINS server.

When a client computer that is configured to use DHCP starts on the first time, it undergoes a series of steps to obtain its TCP/IP configuration information and obtain a lease. A lease is a client computer that receives a full TCP/IP configuration from a DHCP server that a client computer receives TCP/IP configuration information from a DHCP server and typically leases it again after a certain period of time specified by the server.

The brief steps for a client computer to obtain a lease from a DHCP server are: initialization → selection → request → binding. These steps are discussed in more detail below.

Initialization: When the DHCP client computer starts, its IP address does not have any settings. It then sends the DHCP Discover message to the local subnet. The DHCP discover contains the client media access control (MAC) address and the client system name. The MAC address is the only address saved by all network adapters. By using a MAC address in a message, the customer is guaranteed to be uniquely identified on the network.

Option: When a DHCP server receives a DHCP discover message from a client computer, it responds with DHCP offer information. The DHCP offer information contains the MAC address of the client computer, provides the TCP/IP address, the subnet mask, and the IP address of the DHCP server, which is sent directly to the client computer, not to broadcast messages. After the DHCP server sends DHCP offer information, it retains the address sent to the client computer temporarily and waits for the customer who is to obtain the address

Confirmation information.

If the DHCP client does not receive DHCP offer messages with the DHCP server during boot time, it will try to communicate five times with the DHCP server every five minutes. The four retry intervals were 2, 4, 8, 16 seconds, and the other at any interval between 0-100 milliseconds.

Request: When a DHCP client receives a DHCP offer message, it decides which message to use, because there may be multiple DHCP servers on the network, and customers may receive more than one DHCP offer message.

In general, the client computer uses the first message received. The client computer then sends a HDCPREQUEST message to the DHCP server. This message tells the server that the DHCP client accepts the provided TCP/IP address and requires any other configuration information, such as the default gateway address, because the client computer does not have all the DHCP servers to confirm that it has received the TCP/IP address. You still need to use broadcast messages based on the MAC address of the server to pass DHCP request messages to all DHCP servers. This way, if there are other DHCP servers on the web and DHCP offer messages are provided to client computers, they can be released back to the available address pool after they receive broadcast messages.

Binding: When a DHCP Client service DHCP server receives a DHCP request message from a client computer, the DHCP server answers DHCP request with a DHCP ACK message. The DHCP ACK message tells the client computer that it now has a valid lease. The server sends DHCP messages to the client using directed messages, and once the client computer receives the DHCPACK, it completes its own IP configuration and becomes a fully-rented customer.

A DHCP client has a lease that is date and expires. The time period that determines the lease expiration is set by the DHCP server the first time the client system receives a lease. Depending on the time the system takes to receive rollover confirmations from the DHCP server, the customer will extend their leases by rolling over and binding two steps. These two steps are described in detail below.

Rollover: The DHCP client computer sends a DHCP request message to the DHCP server to start the rollover process when half of the lease time is lost. Unless the DHCP client computer is restricted, the server automatically rollover the client lease and make a lease acknowledgement to the client computer by sending a DHCPACK message. Note that the client computer's lease request is a message, not a broadcast, because the DHCP client computer currently has a TCP/IP configuration and is able to communicate with the server using the protocol.

Rebind: The DHCP client computer enters the rebind state when it uses 87.5% of the lease time and the DHCP client computer has not yet extended the lease. At this point, the DHCP client computer broadcasts DHCP request messages to the network, attempting to establish contact with any of the DHCP servers. The DHCP server can then respond with DHCPACK, automatically rollover the client computer lease, or the DHCP server forces the DHCP client computer to start the lease process again.