How DHCP Servers Assign IP Addresses to Hosts

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DHCP (Dynamic Host Configuration Protocol) is a network protocol used by network devices such as routers or servers to automatically assign IP addresses and network configuration information to devices on a network.

DHCP server dynamically assigns IP addresses to hosts in the following way:

Option A: Addresses are permanently assigned so that the host uses the same address at all times. This option is not valid as it goes against the dynamic nature of DHCP, which is intended to allow for flexibility in addressing and network configuration.

Option B: Addresses are assigned for a fixed period of time. At the end of the period, a new request for an address must be made, and another address is then assigned. This option is called the "DHCP lease time." DHCP lease time can be configured to any value according to the network administrator's needs. When a host connects to the network, it broadcasts a DHCP discover message. The DHCP server responds with a DHCP offer message, offering an IP address and network configuration information. If the host accepts the offer, it broadcasts a DHCP request message, requesting the offered IP address. The DHCP server responds with a DHCP acknowledgment message, confirming the assignment of the IP address and the network configuration information to the host. The host can use the assigned IP address and network configuration information for the duration of the lease time. At the end of the lease time, the host must request a new DHCP lease.

Option C: Addresses are leased to hosts. A host will usually keep the same address by periodically contacting the DHCP server to renew the lease. This option is similar to option B, but instead of the host requesting a new DHCP lease at the end of the lease time, the host contacts the DHCP server to renew the lease. The DHCP server checks the lease database to see if the lease is still valid and, if so, renews the lease for the host. If the lease has expired, the DHCP server assigns a new IP address to the host.

Option D: Addresses are allocated after a negotiation between the server and the host to determine the length of the agreement. This option is not valid as there is no negotiation process in DHCP. The DHCP server assigns an IP address and network configuration information to the host based on the DHCP lease time configured on the server.

In summary, DHCP server dynamically assigns IP addresses to hosts by offering an IP address and network configuration information, assigning a lease time, and confirming the assignment with an acknowledgment message. The host can use the assigned IP address and network configuration information for the duration of the lease time, after which it must request a new DHCP lease or renew the lease by contacting the DHCP server.