DHCP principle and configuration

Catalog

What is? DHCP

DHCP The benefits of

DHCP The pattern of

DHCP The way of distribution

DHCP Lease process

experiment ：

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What is? DHCP

DHCP (Dynamic Host Configuration Protocol, Dynamic Host Configuration Protocol ） By Internet Designed and developed by the task force , Used exclusively for TCP/IP Computers in the network automatically assign TCP/IP Protocol of parameters , It's an application layer protocol , Use UDP Of 67 and 68 port .
DHCP The predecessor was BOOTP agreement (BootstrapProtocol),BOOTP It is created to automatically assign addresses to devices connected to the network , Was later DHCP To replace the ,DHCP Than BOOTP More complicated , More powerful .

DHCP The benefits of

Due to the uncertainty of online time and the different technical level of users , Assign a fixed... To each user IP Address , It's not just about IP Waste of address , For ISP Service providers bring high maintenance costs . While using DHCP Services have the following benefits ：

Reduce the workload of Administrators
Avoid the possibility of input errors
avoid IP Address conflict
When changed IP Address segment , There is no need to reconfigure each user's IP Address
Improved IP Address utilization
Facilitate client configuration

DHCP The pattern of

Set up a dedicated computer in the network DHCP The server , Responsible for centralized allocation of various network address parameters （ It mainly includes IP Address 、 Subnet mask 、 Broadcast address 、 Default gateway address 、DNS Server address ）; Other hosts act as DHCP The client , Configure the network card to get the address automatically , Can be with DHCP The server communicates , Complete the automatic configuration process .

DHCP yes C/S Pattern ,DHCP The server and client need to maintain communication ,DHCP be based on  UDP  agreement , Both sides may initiate communication with each other , Therefore, both sides need to listen to the port .

• Server End ：DHCP Server（ function dhcp service ）
• UDP service ： Listening port 67（bootps）
• Client End ：DHCP Client（ function dhcp Program ）
• UDP service ： Listening port 68 （bootpc）

DHCP The way of distribution

• Automatically assigned ： Assigned to a IP Permanent use after address
• Manually assign : from DHCP The server administrator specifically specifies IP Address
• Dynamic allocation : Release the after use IP, For other clients

DHCP Lease process

Client from DHCP Server get IP The process of addressing is called DHCP Lease process
It is divided into 4 A step

1. The client searches the network for servers

2. The server responds to the client service

3. The client sends a service request to the target server

4. The server provides services to the client

① When one DHCP When the client starts , The client has not IP Address , So the client has to go through DHCP Get a legal address

here DHCP The client sends... By broadcast DHCP Discover Find information to look for DHCP The server

②DHCP The server received a request from the client lP Address information when , In their own IP Check the address pool to see if there is any legal IP Address to client

If there is ,DHCP The server will IP Mark the address , Add to DHCP Offer In the news of , Then broadcast a DHCP Offer news

③DHCP The client receives the first DHCP Offer Extract... From the message IP Address , issue IP Address of the DHCP The server keeps the address , In this way, the address can no longer be assigned to another DHCP The client

④DHCP The server receives DHCP Request After the news , With DHCPACK Broadcast a successful acknowledgement to the client in the form of a message , The message contains IP Valid lease and other configurable information for the address

When the client receives DHCPACK When the news , To configure IP Address , complete TCP/IP The initialization

DHCP Every time a client logs back into the network , There is no need to send DHCPDiscover Information , Instead, send directly containing the last assigned IP Address of the DHCP Request Request information

DHCP service

DHCP service

• Automatically assign addresses to a large number of clients , Provide centralized management
• Reduce management and maintenance costs 、 Improve network configuration efficiency

The assignable address information mainly includes

• NIC IP Address 、 Subnet mask
• Corresponding network address 、 Broadcast address
• Default gateway address
• DNS Server address

experiment ：

 

  Configure the layer 2 switch

  Set the interface type , Divide vlan, configure gateway

 

 

  Set the network connection mode for the virtual machine

 

 

  After changing the configuration , Turn on the virtual machine , At this time, the virtual machine cannot log in , Must use root Sign in . Restart NIC , View network card information .

  install dhcp

 

  Get into DHCP Configuration file for , Modify the configuration