Detailed DHCP server workflow (1)

Currently, the general network structure of an enterprise is an internet and an Intranet. A lan merges an Internet. In the LAN Settings, we usually use the relevant protocol settings of the DHCP server. In common small networks, such as the home network and Student Dormitory Network), network administrators use the method of manually assigning IP addresses. However, in medium and large networks, this method is not suitable. In medium and large networks, especially large networks, there are often more than 100 clients. It is not appropriate to manually assign IP addresses. Therefore, we must introduce an efficient IP Address Allocation Method. Fortunately, DHCPDynamic Host Configuration Protocol solves this problem for us.

Advantages and disadvantages of DHCP

DHCP service has many advantages: the network administrator can verify the IP address and other configuration parameters, instead of checking each host. DHCP does not lease the same IP address to both hosts; the DHCP administrator can restrict specific computers to use specific IP addresses. Multiple options can be set for each DHCP scope. clients do not need to reset IP addresses when moving between different subnets.

But there are also many disadvantages: DHCP cannot find IP addresses that are already in use by non-DHCP clients on the network; When Multiple DHCP servers exist on the network, a DHCP server cannot find the IP address that has been rented out by other servers. The DHCP server cannot communicate with clients across vrouters unless the vrobooallows BOOTP forwarding.

Workflow

The DHCP Service works like this:

1. Discovery stage: the stage in which the DHCP Client searches for the DHCP server. The DHCP Client sends DHCP discover discovery information to find the DHCP server in broadcast mode because the IP address of the DHCP server is unknown to the client. That is, it sends specific broadcast information to the IP address 255.255.255.255. Every host installed with TCP/IP protocol on the network will receive this broadcast information, but only the DHCP server will respond 1 ).

2. The provision phase, that is, the IP address provided by the DHCP server. The DHCP server that receives the DHCP discover discovery information in the network will respond, it selects a DHCP client from the IP address that has not been rented, send a DHCP offer containing the IP address for rent and other settings to the DHCP client. 2 ).

3. Select the phase, that is, the IP address provided by a DHCP server is selected by the DHCP client. If Multiple DHCP servers provide information to DHCP offer, the DHCP client accepts only the information provided by the first DHCP offer, then, it answers a DHCP request information in broadcast mode, which contains the content that requests IP addresses from the selected DHCP server. The answer should be broadcast in order to notify all DHCP servers that they will select the IP address provided by a DHCP server 3 ).