In this lab, we will simulate 2 different DHCP server on the same network for failover backup. Our primary DHCP server is 192.168.30.100 and secondary DHCP server is 192.168.100.100 . We have 4 VLANs;
VLAN 10 and VLAN 20 are used for end users. VLAN 30 and VLAN 100 are used for system and network management purposes. We will configure end user VLANs with 2 different DHCP server as primary and secondary. So just in case if any issue happens on first server, devices will be able to get IP addresses from secondary DHCP server.
Cisco does not natively support DHCP failover like Windows DHCP (with lease replication), but we can simulate DHCP backup using:
- DHCP helper addresses (on Layer 3 interface).
- Primary & secondary IP helper-addresses pointing to both servers.
- To set a DHCP server for each VLAN we will use this syntax on CLI “ip helper-address 192.168.x.x“
CORE SWITCH CONFIGURATION
Switch>enable
Switch#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#hostname CORESW
CORESW(config)#vlan 10
CORESW(config-vlan)#vlan 20
CORESW(config-vlan)#vlan 30
CORESW(config-vlan)#exit
CORESW(config)#vlan 100
CORESW(config-vlan)#exit
CORESW(config)#interface vlan 10
CORESW(config-if)#
%LINK-5-CHANGED: Interface Vlan10, changed state to up
CORESW(config-if)#ip address 192.168.10.1 255.255.255.0
CORESW(config-if)#ip helper-address 192.168.30.100
CORESW(config-if)#ip helper-address 192.168.100.100
CORESW(config-if)#no shutdown
CORESW(config-if)#exit
CORESW(config)#interface vlan 20
CORESW(config-if)#
%LINK-5-CHANGED: Interface Vlan20, changed state to up
CORESW(config-if)#ip address 192.168.20.1 255.255.255.0
CORESW(config-if)#ip helper-address 192.168.30.100
CORESW(config-if)#ip helper-address 192.168.100.100
CORESW(config-if)#no shutdown
CORESW(config-if)#exit
CORESW(config)#interface vlan 30
CORESW(config-if)#
%LINK-5-CHANGED: Interface Vlan30, changed state to up
CORESW(config-if)#ip address 192.168.30.1 255.255.255.0
CORESW(config-if)#no shutdown
CORESW(config-if)#exit
CORESW(config)#interface vlan 100
CORESW(config-if)#
%LINK-5-CHANGED: Interface Vlan100, changed state to up
CORESW(config-if)#ip address 192.168.100.1 255.255.255.0
CORESW(config-if)#no shutdown
CORESW(config-if)#exit
CORESW(config)#ip routing
CORESW(config)#interface range g1/0/1-2
CORESW(config-if-range)#switchport mode trunk
CORESW(config-if-range)#
%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/1, changed state to down
%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/1, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan10, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan20, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan30, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan100, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/2, changed state to down
%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/2, changed state to up
CORESW(config-if-range)#switchport trunk allow vlan all
CORESW(config-if-range)#no shutdown
CORESW(config-if-range)#exit
CORESW(config)#interface g1/0/3
CORESW(config-if)#switchport mode access
CORESW(config-if)#switchport access vlan 30
CORESW(config-if)#no shutdown
CORESW(config-if)#description
CORESW(config-if)#description DHCP_SERVER_1
CORESW(config-if)#exit
CORESW(config)#interface g1/0/4
CORESW(config-if)#switchport mode access
CORESW(config-if)#switchport access vlan 100
CORESW(config-if)#description DHCP_SERVER_2
CORESW(config-if)#no shutdown
CORESW(config-if)#exit
CORESW(config)#do copy run start
Destination filename [startup-config]?
Building configuration…
[OK]
ACCESS SWITCH 1 CONFIGURATION
Switch>enable
Switch#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#hostname ACCESS1
ACCESS1(config)#vlan 10
ACCESS1(config-vlan)#vlan 20
ACCESS1(config-vlan)#exit
ACCESS1(config)#interface g1/0/2
ACCESS1(config-if)#switchport mode access
ACCESS1(config-if)#switchport access vlan 10
ACCESS1(config-if)#no shutdown
ACCESS1(config-if)#exit
ACCESS1(config)#interface g1/0/3
ACCESS1(config-if)#switchport mode access
ACCESS1(config-if)#switchport access vlan 20
ACCESS1(config-if)#no shutdown
ACCESS1(config-if)#exit
ACCESS1(config)#interface g1/0/1
ACCESS1(config-if)#switchport mode trunk
ACCESS1(config-if)#switchport trunk allow vlan all
ACCESS1(config-if)#no shutdown
ACCESS1(config-if)#exit
ACCESS1(config)#do copy run start
Destination filename [startup-config]?
Building configuration…
[OK]
ACCESS SWITCH 2 CONFIGURATION
Switch>enable
Switch#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#hostname ACCESS2
ACCESS2(config)#interface g1/0/1
ACCESS2(config-if)#switchport mode trunk
ACCESS2(config-if)#switchport trunk allow vlan all
ACCESS2(config-if)#no shutdown
ACCESS2(config-if)#exit
ACCESS2(config)#vlan 10
ACCESS2(config-vlan)#exit
ACCESS2(config)#vlan 20
ACCESS2(config-vlan)#exit
ACCESS2(config)#interface g1/0/2
ACCESS2(config-if)#switchport mode acc
ACCESS2(config-if)#switchport access vlan 10
ACCESS2(config-if)#no shutdown
ACCESS2(config-if)#exit
ACCESS2(config)#interface g1/0/3
ACCESS2(config-if)#switchport mode access
ACCESS2(config-if)#switchport access vlan 20
ACCESS2(config-if)#no shutdown
ACCESS2(config-if)#exit
ACCESS2(config)#do copy run start
Destination filename [startup-config]?
Building configuration…
[OK]
DHCP SERVER 1 192.168.30.100 (vlan 30)
DHCP SERVER 2 192.168.100.100 (vlan 100)
We set the same IP subnets on both servers as shown.
FAILOVER TEST
We will shutdown the first DHCP server to see if our config is working fine. After shutting down first DHCP server, go to one end user computer and from Desktop tab, click on DHCP option then it should receive an automatic IP address from assigned subnet.
If you have any further questions, dont hesitate to contact with me.
Happy networking đŸ™‚
You can download the Cisco Packet Tracer simulation from this link
