8 message types and feature servers for DHCP protocol

Source: Internet
Author: User
Tags ack

1) The host sends a DHCP Discover broadcast packet looking for a DHCP server on the network; unicast packets, addresses,
2) The DHCP server sends DHCP offer unicast packets to the host, including IP address, MAC domain name information, and address lease, address, domain name information, and the lease period;
3) The host sends a DHCP request broadcast packet, formally requesting the server to allocate the provided IP address;
4) unicast packet, confirm the request of the host. The DHCP server sends a DHCP ACK unicast packet to the host to confirm the host's request. Description: The packet, Description: The DHCP client can receive DHCP offer packets for multiple DHCP servers, and then the packet may accept any one of the DHCP offer packets, but the client usually only accepts the first packet received. Additionally, a DHCP offer packet. In addition, the address specified in the DHCP server DHCP offer differs from the final assigned address, which is typically the final assigned address, and typically the DHCP server retains the address until a formal request is made by the client. The official request. A broadcast packet is used to formally request the DHCP server to assign an address DHCP request uses a broadcast packet so that other servers can also receive the packet, and all DHCP servers that send DHCP offer packets are able to receive the packet and then release the pre-allocated address. The IP address of the client has been offered (pre-allocated). The packet contains invalid configuration parameters.
5) If the DHCP Offer packet sent to the DHCP client contains invalid configuration parameters, the guest packet refuses to accept the configuration information that has already been allocated. The client sends a DHCP decline packet to the server to refuse to accept the configuration information that has already been allocated. Information packets,
6) When the DHCP client sends a DHCP Request packet, the server rejects the Address Assignment table when responding to the DHCP ACK packet (the DHCP server finds the IP address Allocation table based on the MAC address in the Request packet, does not find its assigned address), and the DHCP Address), the DHCP server sends a DHCP NAK message to the DHCP client, causing the client to re-initiate the address request process. The process of re-initiating the address request. Release
7) DHCP client can send DHCP Release message to DHCP server discard network address and cancel existing lease message request configuration parameters only
(8) DHCP client can send DHCP Inform message to DHCP server only request configuration parameter (client address) machine already has IP address)


DHCP works as follows:
① when the DHCP client starts, the client broadcasts the DHCPDISCOVER message in the current subnet and requests an IP address from the DHCP server. After the
②dhcp   server receives the dhcpdiscover   message, it will provide it with a
   ip address that has not been assigned to the address in respect of that host. And temporarily mark the provided IP address as unavailable. The server is sent back to the host with a DHCPOFFER message. If the network contains more than
    one DHCP server, the client may receive several DHCPOFFER messages, the client will generally only recognize the first dhcpoffer. The
③ client receives Dhcpoffer and sends a DHCPREQUEST message to the server that contains the IP address provided by the DHCP server. If the
    client does not receive the dhcpoffer   message and remembers the previous network configuration, use the previous network configuration (if the configuration is still
    Validity period)
The ④DHCP server sends back to the client a reply (DHCPACK) that contains the IP address of the tablet and its allocation scheme. After the
⑤ client receives the DHCPACK message that contains the configuration parameters, it uses ARP to check for the same IP address on the network. If the check passes,
    the client receives the IP address and its parameters, and if a problem is found, the client sends DHCPDecline information to the server and restarts the
    The new configuration process. The server receives DHCPDecline information and marks the address as unavailable. The
⑥DHCP server can only assign that IP address to a DHCP client for a certain amount of time, and the DHCP client must update it before the lease expires. The
    client leases before the DHCP server update starts at intervals after 50% lease time has elapsed. If the DHCP server answers, rent
    postpone; If the DHCP server does not answer at all, the customer should contact any other DHCP server for a valid lease of 87.5%.

8 message types and feature servers for the DHCP protocol

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