DHCP review

(centos7)

brief introduction

Dynamic Host Configuration Protocol （DHCP） It's a kind of be based on UDP agreement And only in LAN Network protocol used internally , It is mainly used in large LAN environment or LAN environment with many mobile office devices , The purpose is to automatically allocate data for equipment or network suppliers within the LAN IP Address and other parameters , Provides information about network configuration “ Family bucket ” service .

dhcpd yes Linux Used in the system to provide DHCP The service procedure of . The package name is dhcp-server

DHCP Common terms involved

• Scope ： A complete IP Address segment ,DHCP Manage the distribution of the network according to the scope 、IP Address assignment and other configuration parameters .
• Superscope ： Used to manage multiple logical subnet segments in the same physical network , It contains a list of scopes that can be managed uniformly .
• Exclusion range ： Put some... In scope IP Address exclusion , Make sure these IP The address will not be assigned to DHCP client .
• Address pool ： Is defined. DHCP After the exclusion scope is applied , The rest is used to dynamically allocate to the client IP Address range .
• lease ：DHCP The client can use dynamically allocated IP Time of address .
• make an appointment ： Ensure that specific devices in the network always get the same IP Address .

working principle

One . Four steps to lease

2.1 DHCP Client to IP request

2.2 DHCP Server responds to requests

2.3 DHCP Client selection IP

2.4 DHCP Server confirms lease

Two . Renewal

/etc/dhcp/dhcpd.conf

#
# DHCP Server Configuration file.
# see /usr/share/doc/dhcp-server/dhcpd.conf.example
# see dhcpd.conf(5) man page
#

 dhcpd Common parameters and functions used in the service program configuration file 

 Parameters 	 effect 
ddns-update-style  type 	 Definition DNS The type of service dynamic update , Types include ：
none（ Dynamic update not supported ）、interim（ Interactive update mode ） And ad-hoc（ Special update mode ）
allow/ignore client-updates	 allow / Ignore client updates DNS Record 
default-lease-time 21600	 Default timeout 
max-lease-time 43200	 Maximum timeout 
option domain-name-servers 8.8.8.8	 Definition DNS Server address 
option domain-name "domain.org"	 Definition DNS domain name 
range	 Define the IP Address pool 
option subnet-mask	 Define the subnet mask for the client 
option routers	 Define the gateway address of the client 
broadcast-address  Broadcast address 	 Define the broadcast address of the client 
ntp-server IP Address 	 Define the client's network time server （NTP）
nis-servers IP Address 	 Define client's NIS Address of domain server 
hardware  Hardware type  MAC Address 	 Specify the type of network card interface and MAC Address 
server-name  Host name 	 towards DHCP Client notification DHCP The hostname of the server 
fixed-address IP Address 	 To fix something IP Address assigned to the specified host 
time-offset  Offset difference 	 Specifies the offset difference between the client and Greenwich mean time 

[[email protected] ~]# vim /etc/dhcp/dhcpd.conf
ddns-update-style none;					 Set up DNS The service does not automatically update dynamically 
ignore client-updates;					 Ignore client updates DNS Record 
subnet 192.168.10.0 netmask 255.255.255.0 {
    		 The scope is 192.168.10.0/24 Network segment 
        range 192.168.10.50 192.168.10.150;		IP The address pool is 192.168.10.50-150（ about 100 individual IP Address ）
        option subnet-mask 255.255.255.0;		 Define the client's default subnet mask 
        option routers 192.168.10.1;			 Define the gateway address of the client 
        option domain-name "linuxprobe.com";	 Define default search fields 
        option domain-name-servers 192.168.10.1;  Define client's DNS Address 
        default-lease-time 21600;				 Define the default lease time （ Company ： second ）
        max-lease-time 43200;					 Define the maximum appointment time （ Company ： second ）
}


 firewall-cmd --zone=public --permanent --add-service=dhcp
 firewall-cmd --reload

experiment

1. Basic experiments

server

yum install -y dhcp

vim /etc/dhcp/dhcpd.conf

subnet 192.168.10.0 netmask 255.255.255.0 {
    
        range 192.168.10.50 192.168.10.150;
        option subnet-mask 255.255.255.0;
     # option routers 192.168.10.1;
     # option domain-name "linuxprobe.com";
     # option domain-name-servers 192.168.10.1;
        default-lease-time 21600;
        max-lease-time 43200;

service dhcpd restart 


tail /var/log/message

Jun 20 07:20:11 localhost systemd: Started DHCPv4 Server Daemon.
Jun 20 07:20:13 localhost dhcpd: DHCPDISCOVER from 00:0c:29:d9:5e:93 via ens33
Jun 20 07:20:14 localhost dhcpd: DHCPOFFER on 192.168.10.50 to 00:0c:29:d9:5e:93 via ens33
Jun 20 07:20:14 localhost dhcpd: DHCPREQUEST for 192.168.10.50 (192.168.10.10) from 00:0c:29:d9:5e:93 via ens33
Jun 20 07:20:14 localhost dhcpd: DHCPACK on 192.168.10.50 to 00:0c:29:d9:5e:93 via ens33

2. Fixed address assignment

client

arp -a #  obtain mac

server

host test {
    
        hardware ethernet 00:0c:29:e3:2d:08
        fixed-address 192.168.10.160
}

3. Superscope

Can solve ip Not enough address , One arm router

server

cp -a /etc/sysconfig/network-scripts/ifcfg-ens33 /etc/sysconfig/network-scripts/ifcfg-ens33:1

 Change devcive,ipaddr

vim /etc/sysctl.conf
net.ipv4.ip_forward = 1

sysctl -p

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

vim /etc/dhcp/dhcpd.conf

:1,88d



shared-network 10-20 {
    
  subnet 192.168.10.0 netmask 255.255.255.0 {
    
    option routers 192.168.10.10;
    range 192.168.10.200 192.168.10.200;
  }
  subnet 192.168.20.0 netmask 255.255.255.0 {
    
    option routers 192.168.20.10;
    range 192.168.20.100 192.168.20.200;
  }
}

4. dhcp Relay server

dhcp The server vm10 192.168.10.10

vim /etc/sysconfig/network-scripts/ifcfg-ens33
IPADDR=192.168.10.10
NETMASK=255.255.255.0
DNS1=8.8.8.8
GATEWAY=192.168.10.20

service network restart
yum install dhcp -y 

vim /etc/dhcp/dhcpd.conf

subnet 192.168.10.0 netmask 255.255.255.0 {
    
  range 192.168.10.100 192.168.10.110;
  option routers 192.168.10.20;
}
subnet 100.100.100.0 netmask 255.255.255.0 {
    
  range 100.100.100.100 100.100.100.110;
  option routers 100.100.100.20;
}

dhcp relay vm10 192.168.10.20 vm11 100.100.100.20

vim /etc/sysconfig/network-scripts/ifcfg-ens33
IPADDR=192.168.10.20
NETMASK=255.255.255.0
DNS1=8.8.8.8
GATEWAY=192.168.10.20

vim /etc/sysconfig/network-scripts/ifcfg-ens34
IPADDR=100.100.100.10
NETMASK=255.255.255.0
DNS1=8.8.8.8
GATEWAY=100.100.100.20

service network restart
yum install dhcp -y 

cp /lib/systemd/system/dhcrelay.service /etc/systemd/system   # take dhcp Relay master configuration file replication 
vim /etc/systemd/system/dhcrelay.service                      # edit dhcp Relay master configuration file 

[Service]
Type=notify
ExecStart=/usr/sbin/dhcrelay -d --no-pid -i ens33 -i ens35 192.168.10.10




vim /etc/sysctl.conf 
net.ipv4.ip_forward = 1

sysctl -p

topic

https://www.linuxprobe.com/basic-learning-14.html