How to build a DHCP server in Linux

systemctl start dhcpd

cp /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example /etc/dhcp/dhcpd.conf

  7 option domain-name "server.com"; 
      ##Domain name: see /etc/resolv.conf
  8 option domain-name-servers 172.25.10.254;
      ##Specify DNS servers, separate multiple servers with commas.
 30 subnet 172.25.10.0 netmask 255.255.255.0 {
      ##Specify subnet and subnet mask 31 range 172.25.10.10 172.25.10.20;
      ##Specify IP range 32 option routers 172.25.10.254;
 ##Specify the default gateway 33 }
 34#### Delete lines 27, 28, 34 and beyond

DEVICE=eth0
BOOTPROTO=dhcp
###The key part is dhcp
ONBOOT=yes

systemctl restart network
###In this experiment, I encountered the following problem: an error occurred when executing the command, and an IP address could not be obtained through the DHCP server. The solution is: DHCP is usually a communication protocol used in a local area network. It mainly sends broadcast data packets to all hosts in the entire physical network segment through the client. Only when there is a DHCP server in the local area network will it respond to the client's IP parameter requirements. Therefore, the DHCP server and client should be in the same physical network segment. The entire DHCP packet interaction between the server and the client is shown in Figure (1):
###So I guess the firewall is blocking the transmission of data packets###The solution I took is:
Both virtual machines execute the command:
firewall-cmd --permanent --add-service=dhcp
firewall-cmd --reload 
Check whether DHCP is working:
firewall-cmd --list-all
The problem is solved after restarting the virtual machine. 

#dhcpd.conf
#
# Sample configuration file for ISC dhcpd
#

# option definitions common to all supported networks...
option domain-name "example.org";
option domain-name-servers 192.168.0.199;

default-lease-time 600;
max-lease-time 7200;

# Use this to enable / disable dynamic dns updates globally.
#ddns-update-style none;

# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
#authoritative;

# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;

# No service will be given on this subnet, but declaring it helps the 
# DHCP server to understand the network topology.


# This is a very basic subnet declaration.

subnet 192.168.0.0 netmask 255.255.255.0 {
  range 192.168.0.10 192.168.0.20;
  option routers 192.168.0.199;
}