DHCP dynamic host allocation protocol, widely used in the usual Internet, such as the router for home Internet is a DHCP server. When we set the client to automatically acquire the IP address, the DHCP server assigns the IP address to the client according to the DHCP protocol. The ONU can also be used as a DHCP server.
There are four main messages of DHCP protocol:
DHCP Discover: Send out by the client to discover the DHCP server.
DHCP Offer: Send by the DHCP server, tells the client that I can provide the IP address.
DHCP Request: Send by the client tells the corresponding DHCP server that I need the IP address.
DHCP ACK: Issued by the DHCP server to provide the IP address of the client response.
DHCP Release: Generally, the client is shut down or offline. This message will cause the DHCP server to release the IP address of the client that sends this message.
DHCP Inform: A message sent by the client that requests some information from the server.
DHCP Decline: When the client finds that the IP address assigned by the server is not available (such as IP address conflicts), this message is issued informing the server against the use of the IP address.
During DHCP communication, UDP is used as the transmission protocol. The host sends a request to the DHCP server port 67 and the server replies the message to the host port 68.
1. Discovery stage, the DHCP client finding DHCP server (DHCP discover)
The DHCP client sends DHCP discover discovery information by broadcast (because the DHCP is unknown the IP address for the client) to find the DHCP server, i. e. a specific broadcast information to the address 255.255.255.255. Every host on the network with the TCP / IP protocol installed receives this broadcast message, but only the DHCP server responds.
2. Supply stage, the stage when the DHCP server provides the IP address (DHCP offer)
The DHCP server that receives DHCP discover discovery information in the network responds, selecting an IP address that has not yet been leased to a DHCP client and sending the DHCP client a DHCP offer containing the leased IP address and other settings.
3. Selection stage, the stage when the DHCP client selects the IP address provided by a DHCP server (DHCP request)
If there are multiple DHCP and the server provides information to the DHCP offer sent by the DHCP client, the DHCP client accepts only the first received DHCP offer, and then broadcasts a DHCP request request information that requests the IP address from the DHCP server it selected. The broadcast answer is to notify all DHCP servers that he will select the IP address provided by a DHCP server.
4. Validation stage, when the DHCP server confirmed the provided IP address (DHCPack)
When the DHCP server receives the DHCP request request information answered by the DHCP client, it sends a DHCPack containing the client IP address and other settings to the DHCP client, confirming the information and telling the DHCP client to use the IP address it provides. Then the DHCP client will bind its TCP / IP protocol with the network card. In addition, except for the servers selected by the DHCP client, other DHCP servers will recover the IP address provided.
5. Re-login (DHCP request)
Every time the DHCP client logs on to the network, it does not need to send DHCP discover discovery information, but directly sends DHCP request request information containing the previous assigned IP address. When the DHCP server receives this message, it will try to get the DHCP client to continue with the original IP address and answer a DHCPack confirmation message. If this IP address is no longer assigned to the original DHCP client (more than this IP address has been assigned to another DHCP client), DHCP, the server answers an DHCPnack denial message to the DHCP client. When the original DHCP client receives this DHCPnack denial message, it must reissue the DHCP discover discovery message to request a new IP address.
6. Update the lease
DHCP, the IP address leased by the server to DHCP clients generally has a lease period, and the DHCP server will take back the leased IP address upon expiration. If the DHCP client is to extend its IP lease, it must update its IP lease. When the DHCP client starts and during the IP lease period, the DHCP client automatically sends information to the DHCP server to update its IP lease.
DHCP Dynamic host allocation is also one of our ONU series network products, and the popular network products of our company cover various types of ONU series products, including AC ONU / communication ONU / intelligent ONU / box ONU / double ON port ONU, etc. The above ONU series products can be used for the network requirements of each scene. Welcome to have a more detailed technical understanding of the products.