Shulou(Shulou.com)06/02 Report--

DHCP message type description

1. When the DHCP Discover DHCP client requests the address, it does not know the location of the DHCP server, so the DHCP client will broadcast the request message in the local network. This message becomes the Discover message, and the purpose is to find the DHCP server in the network. All the DHCP servers that receive the Discover message will send a response message, so the DHCP client can know the location of the DHCP server that exists in the network.

2. After receiving the Discover message, the DHCP Offer DHCP server will look for a suitable ip address in the configured address pool, add the corresponding lease term and other configuration information (gateway, DNS server, etc.), construct an Offer message, send it to the customer, and inform the user that the server can provide it with an IP address. (just tell client that it can be provided, it is pre-allocated, and client is required to detect whether the IP is duplicated through ARP.)

3. The DHCP Request DHCP client will receive a lot of Offer, so you must choose one of these responses. Client usually chooses the first server that responds to Offer messages as its target server, and responds to a broadcast Request message to advertise the selected server. After the DHCP client has successfully obtained the IP address, it will send a unicast Request message to the DHCP server to renew the lease period when the address has used the lease term 1 to 2. If it does not receive the DHCP ACK message, it will send a broadcast Request message to extend the lease period when the lease term has passed 3 times 4.

4. After receiving the Request message, the DHCP ACK DHCP server looks for the corresponding renewal record according to the user MAC carried in the Request message, and if so, sends the ACK message in response, informing the user that the assigned ip address can be used.

5. DHCP NAK if the DHCP server does not find the corresponding lease record after receiving the Request message or cannot properly assign the ip address for some reason, it will send the ACK message in response, informing the user that the appropriate ip address cannot be assigned.

6. When the user no longer needs to assign an ip address, DHCP Release will send a Release message to the DHCP server, informing the server that the user no longer needs to assign an ip address, and the DHCP server will release the bound lease.

7. After receiving the ACK message from the DHCP server, the DHCP Decline DHCP client sends a Decline message to inform the server that the assigned ip address is unavailable if it finds that the address assigned by the server conflicts or cannot be used for other reasons.

8. If the DHCP Inform DHCP client needs to obtain more detailed configuration information from the DHCP server, it sends an Inform message to the server to make a request. After receiving the message, the server will find it according to the lease, find the corresponding configuration information, and send an ACK message to respond to the DHCP client (rarely used).

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