Explain how to configure a Linux server to act as a DHCP server, including the essential configuration file and parameters.

To configure a Linux server to act as a DHCP (Dynamic Host Configuration Protocol) server, you need to install a DHCP server software package, configure its settings, and enable the service. One of the most common DHCP server packages is `isc-dhcp-server`. First, install the `isc-dhcp-server` package using your distribution's package manager. For example, on Debian-based systems, you would use the command `sudo apt-get install isc-dhcp-server`. On Red Hat-based systems, you would use the command `sudo yum install dhcp`. Second, configure the DHCP server settings in the configuration file. The essential configuration file for `isc-dhcp-server` is `/etc/dhcp/dhcpd.conf`. You will need to edit this file to define the DHCP server's settings, such as the IP address range to assign, the default gateway, and the DNS servers. Important parameters in the `/etc/dhcp/dhcpd.conf` file include: `subnet`: Defines the subnet for which the DHCP server will provide addresses. For example: `subnet 192.168.1.0 netmask 255.255.255.0`. `range`: Specifies the range of IP addresses that the DHCP server can assign. For example: `range 192.168.1.100 192.168.1.200`. `option routers`: Sets the default gateway for the clients. For example: `option routers 192.168.1.1`. `option domain-name-servers`: Specifies the DNS servers for the clients. For example: `option domain-name-servers 8.8.8.8, 8.8.4.4`. `default-lease-time`: Sets the default lease time for IP addresses. For example: `default-lease-time 600`. `max-lease-time`: Sets the maximum lease time for IP addresses. For example: `max-lease-time 7200`. You can also define static IP address assignments for specific devices based on their MAC addresses using the `host` directive. For example: `host printer { hardware ethernet 00:11:22:33:44:55; fixed-address 192.168.1.50; }`. Third, specify the network interface on which the DHCP server should listen for requests. This is typically done in the `/etc/default/isc-dhcp-server` file (on Debian-based systems) or in the `/etc/sysconfig/dhcpd` file (on Red Hat-based systems). Set the `INTERFACES` variable to the name of the network interface. For example: `INTERFACES="eth0"`. Fourth, start and enable the DHCP server service. Use the following commands to start and enable the service: `sudo systemctl start isc-dhcp-server` and `sudo systemctl enable isc-dhcp-server`. Fifth, verify that the DHCP server is working correctly by connecting a client device to the network and checking if it receives an IP address from the DHCP server. You can also examine the DHCP server logs (typically located in `/var/log/syslog` or `/var/log/messages`) for any errors or warnings.