Cisco router configuration DHCP service and relay
topology
The network segment on the LAN side of R1 is and 192.168.10.0/24the default gateway is192.168.10.1
The network segment on the R2 LAN side is and 192.168.20.0/24the default gateway is192.168.20.1
The DNS server address is192.168.10.2
The address of G0/0 of R0 is10.1.1.1
The G0/1 address of R0 is10.1.1.2
configuration
Exclude addresses from the pool
The purpose of excluding IP addresses is to reserve some fixed IPs to prevent conflicts caused by the allocation of the IPs.
For example, exclude the first 10 IPs of R1 and 192.168.10.254(note that the configuration is on R0)
R0(config)#ip dhcp excluded-address 192.168.10.1 192.168.10.10
R0(config)#ip dhcp excluded-address 192.168.10.254
This process is the same for R2.
Create and configure a DHCP address pool
Create an address pool on R0 for the R1 LAN side
R0(config)#ip dhcp pool R1-LAN
set network address
R0(dhcp-config)#network 192.168.10.0 255.255.255.0
Specify the default gateway for this network
R0(dhcp-config)#Default-router 192.168.10.1
specify DNS server
R0(dhcp-config)#dns-server 192.168.10.2
Configure the domain name (you can not match it if there is no requirement)
R0(dhcp-config)#domain-server example.com
relay
Enter the G0/0 interface configuration mode of R1
R1(config)#interface g0/0
Set helper-address (the configured address is the interface of R0 closest to R1)
R1(config-if)#ip helper-address 10.1.1.1
Note: If a single DHCP provides DHCP service, the helper-address address is the DHCP server address (as shown in the figure below)
At this time, the command in the R1 G0/0 interface configuration mode in the above figure is
R1(config-if)#ip helper-address 192.168.11.6
Precautions
Cisco routers enable DHCP service by default. To disable it, execute the following command
Router(config)#no service dhcp