In this post, I would like to show you the steps you need to take in order to configure a DHCP server on a Cisco router.

If your router or switch does not have any configuration on it, you can follow these steps for adding a basic configuration: 8 easy steps for basic Cisco switch configuration.

If you are looking to pass the CCNA exam, be aware that DHCP configuration is included in the requirements for the CCNA certification. You can find the list of exam topics here.

Define the excluded IP addresses from the DHCP pool

Before starting to configure the DHCP server on your router, you need to think about how many IP addresses should be excluded from the pool. These IP addresses will be assigned as static IP addresses to different devices which require a static IP address. For example your router, switch or server.

On the router, you need to run a similar command. Please adjust the commands according to your environment.

R2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#ip dhcp excluded-address 192.168.100.1 192.168.100.100
R2(config)#

Configure the DHCP pool

After identifying the static IP addresses which were excluded from the pool, you need to define a pool on the router. The DHCP clients will receive an IP address dynamically from this pool.

Add the following command on your router:

ip dhcp pool DHCPRouter # define a name according to your needs

Define the IP subnet

After creating the DHCP pool, you need to configure the subnet /network from which the IP addresses will be allocated to the clients.

Run a similar command on your router. Adjust it according to your environment.

R2(config)#ip dhcp pool DHCPRouter
R2(dhcp-config)#network 192.168.100.0 255.255.255.0
R2(dhcp-config)#

Specify the default router used by your DHCP clients

Next, you need to specify the default router (gateway) which will be allocated to your DHCP clients.

default-router 192.168.100.1

Specify the DNS server used by your DHCP clients

If you also want to assign a DNS server dynamically to your DHCP clients, you need to add a similar command on your router.

dns-server 192.168.100.1

Specify the domain name used by your DHCP clients

If your hosts are part of a domain and you want it added to your DCHP clients, you need to configure the domain name.

domain-name gulian.uk

Configure the lease time

By default, the Cisco router allocates the IP address to your DHCP clients for 1 day. If you want to change the default lease time, you can change it with the lease command:

R2(config)#ip dhcp pool DHCPRouter
R2(dhcp-config)#lease ?
  <0-365>   Days
  infinite  Infinite lease

R2(dhcp-config)#lease 7
R2(dhcp-config)#

Save the config and test if the DHCP server is working properly

The last step you need to take is to save the running-config to startup-config and to test if the DHCP server is working as intended.

R2#copy running-config startup-config
Destination filename [startup-config]? 
Building configuration...


  [OK]
R2#

In my lab, I will use 2 clients – a Cisco switch and a Ubuntu laptop – in order to test if DHCP server is working properly.

I will start with the Cisco switch. The switch is connected to the Cisco router via an Ethernet cable. The switch interface is configured to acquire its IP address through the DHCP protocol.

SW1#show running-config interface fastEthernet 0/24
Building configuration...

Current configuration : 66 bytes
!
interface FastEthernet0/24
 no switchport
 ip address dhcp
end

SW1#show ip int brief fastEthernet 0/24            
Interface              IP-Address      OK? Method Status                Protocol
FastEthernet0/24       192.168.100.103 YES DHCP   up                    up      
SW1#

For more details regarding your DHCP server and the IP address allocated to your switch run the below commands.

show dhcp server
show dhcp lease

Lets see if the Ubuntu laptop received an IP address from the DHCP server running on the Cisco router.

It seems that the DHCP server is working properly and the clients are able to acquire the IP address via DHCP protocol.

If you want to check the statistics for your DHCP server, you need to run the below command:

R2#show ip dhcp server statistics 
Memory usage         57602
Address pools        1
Database agents      0
Automatic bindings   2
Manual bindings      0
Expired bindings     0
Malformed messages   0
Secure arp entries   0

Message              Received
BOOTREQUEST          0
DHCPDISCOVER         19
DHCPREQUEST          8
DHCPDECLINE          0
DHCPRELEASE          3
DHCPINFORM           0

Message              Sent
BOOTREPLY            0
DHCPOFFER            6
DHCPACK              6
DHCPNAK              2
R2#

To find out how many clients are using IP addresses from your DHCP pool, run a similar command on your device.

R2#show ip dhcp binding 
Bindings from all pools not associated with VRF:
IP address          Client-ID/	 	    Lease expiration        Type
		    Hardware address/
		    User name
192.168.100.101     01f8.b46a.ba31.38       Apr 02 2023 12:25 PM    Automatic
192.168.100.103     0063.6973.636f.2d65.    Mar 27 2023 12:12 PM    Automatic
                    3862.612e.3730.3930.
                    2e61.3034.312d.4661.
                    302f.3234
R2#

I hope you find this post useful. Share it on your social media channels so that other people can read it too.