Application and principle of DHCP in Enterprise Network Park

First, DHCP Introduction:

DHCP Full name Dynamic Host Configuration Protocol (Dynamics host Configuration Protoco), commonly used in local area network, using UDP protocol, is mainly used to assign IP addresses to machines in the internal network, so as to facilitate administrators to centrally manage the IP allocation of computers in the network.

Two, the composition of the DHCP:

It consists of the server side and the client. The server side is responsible for processing client DHCP requests. Negotiate with the client, and then assign an IP address to the client.

Three, DHCP address allocation is divided into three ways:

Human allocation: Also known as static IP, often for some servers or a few special features of the computer binding fixed permanent IP.

Automatic allocation: Automatically assigns the IP address to the client, and the lease period is permanent.

Dynamic allocation: This approach is now most commonly used to assign temporary IP addresses to clients.

The difference between four or three ways of distribution:

Single scope: manages a single scope. Contains only one network.

Superscope: can contain multiple DHCP scopes to contain multiple subnets. Use two DHCP servers to manage separate logical IP networks on the same physical network segment. A flat based network.

DHCP Relay: A network that belongs to a hierarchy.

V. The process of dynamic distribution mode:

Diagram:

1. The client uses 0.0.0.0 broadcast address to send DHCP Discover packets, waiting for the DHCP server to answer

2. After receiving the message, the DHCP server returns a DHCP offer, and the client receives the DHCPREQUEST packet, which includes the IP address of the server providing the offers.

3. When other DHCP servers receive DHCP request messages, their own offer messages are recycled.

4. The server that provides the offer information sends the client a DHCP ACK acknowledgement message, and the client will initialize its TCP/IP protocol again after receiving it.

VI. procedures for DHCP clients to update addresses:

Because dynamically assigned leases are temporary, the DHCP client automatically attempts to renew leases when the lease duration reaches 50%. Sends a dhcprequest, and if the server receives it, it sends a dhcpack, and if the server is down, the client continues to use the current configuration information. When the lease expires at 87.5%, the client broadcasts a DHCPDISCOVER message to update his lease. If you receive a server-side DHCP offer message response at this time, the current lease is updated, the client can continue to use it normally, and if there is no response, continue to use the previous IP configuration information. If the lease time reaches 100% (the lease expires), the client must release the IP address that is currently in use. The client then sends the DCHP discover again, waiting for a response.

(Attached: The file for viewing leases in Linux is:/var/lib/dhcpd/dhcpd.leases)