Network management basics: DHCP servers

As an administrator, DHCP servers cannot be unfamiliar. Here we will explain the relevant knowledge. DHCP is short for Dynamic Host Configuration Protocol. It is a type of TCP/IP Protocol cluster and is mainly used to assign Dynamic IP addresses to network clients. These allocated IP addresses are a set of IP addresses reserved by the DHCP server in advance, and they are generally consecutive IP addresses.

Understanding DHCP Service

When using DHCP, you must have a DHCP server on the network, while other machines execute DHCP clients. When the DHCP client sends a message requesting a dynamic IP address, the DHCP server will provide an available IP address and subnet mask to the client based on the configured IP address.

1. Advantages of DHCP

DHCP enables the server to dynamically provide IP addresses for other servers in the network. By using DHCP, you do not need to set or maintain static IP addresses for any server except DHCP, DNS, and WINS servers in the Intranet. Using DHCP can greatly simplify the configuration of client TCP/IP, especially when some TCP/IP parameters change, such as the IP address and subnet mask changes caused by large-scale network reconstruction.

A DHCP Server is a computer running Microsoft TCP/IP, DHCP Server software, and Windows NT Server. a dhcp client is a TCP/IP host that requests TCP/IP configuration information. DHCP uses the client/server model. The network administrator can create one or more DHCP servers that maintain TCP/IP configuration information and provide it to the client.

The IP address database on the DHCP server contains the following items:

● Valid configuration parameters for all clients on the Internet.

● The valid IP address specified for the client in the buffer pool and the reserved IP address manually specified.

● The server provides the lease time, which is the time available for the specified IP address.

Configuring a DHCP server in the network has the following advantages:

● Administrators can specify TCP/IP parameters for common and specific subnets for the entire Internet, and define the parameters of clients that use reserved addresses.

● Provides secure and trusted configurations. DHCP avoids configuration errors caused by manually entering numbers on each computer and prevents Computer Configuration address conflicts on the network.

● Using a DHCP server can greatly reduce the configuration overhead and reconfigure the computer time on the network. The server can configure all additional configuration values when assigning an address lease.

● The client does not need to manually Configure TCP/IP.

● When the client moves between subnets, the old IP address is automatically released for reuse. When the client is started again, the DHCP server will automatically reconfigure the TCP/IP for the client.

● Most routers can forward DHCP configuration requests. Therefore, no DHCP server is required for each subnet on the Internet.

Note: If you want to use a DHCP server to support subnets that span multiple routers, the router may need hardware upgrades. The vro must support RFC 1533, 1534, 1541, and 1542.

2. DHCP Address Allocation Method

DHCP uses the Client/Server mode. The Network Administrator establishes one or more DHCP servers and saves the TCP/IP configuration information that can be provided to the client. This information includes the valid configuration parameters of the network customer, the valid IP address pool allocated to the customer (including the address reserved for manual configuration), and the lease duration provided by the server.

If you set a computer on a TCP/IP network to obtain an IP address from a DHCP server, these computers become DHCP clients. When a DHCP Client is started, it communicates with the DHCP server to receive necessary TCP/IP configuration information. The configuration information must contain at least one IP address, subnet mask, and lease related to the configuration.

The DHCP server can assign TCP/IP addresses to DHCP clients in three ways:

● Manual allocation: during manual allocation, the network administrator manually configures the IP address of the DHCP client on the DHCP server. When the DHCP client requires network services, the DHCP server passes the manually configured IP address to the DHCP client.

● Automatic allocation: in automatic allocation, no manual IP Address Allocation is required. After a DHCP Client rents an IP address from the DHCP server for the first time, the IP address is permanently assigned to the DHCP Client, instead of being assigned to other clients.

● Dynamic Allocation: When a DHCP Client rents an IP address from the DHCP server, the DHCP server only temporarily assigns an IP address to the client. Once the lease term expires, the address will be returned to the DHCP server for use by other clients. If the DHCP Client still needs an IP address to complete the work, you can request another IP address.

The dynamic allocation method is the only method that can automatically reuse IP addresses. It is especially convenient for DHCP clients temporarily connected to the Internet, it is also a good way to assign IP addresses to new hosts that are permanently connected to the network. The DHCP client gives up the IP address when it no longer needs it. If the DHCP client needs to shut down normally, it can release the IP address to the DHCP server, then, the DHCP server can assign the IP address to the DHCP Client requesting the IP address.

The dynamic allocation method can solve the problem of insufficient IP addresses. For example, a class C network supports only 254 hosts, and more than three hundred hosts on the network, however, if there are a maximum of 200 users online at the same time, manual or automatic allocation will not solve this problem. The IP address in the dynamic allocation mode is not always assigned to a client. If there is an idle IP address, the DHCP server can allocate it to the client with the required IP address. When the client no longer needs an IP address, the DHCP server recovers the instance.