Configure DHCP on Cisco Router

Configuring DHCP on a Cisco router is a key skill for every network administrator. DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses to devices on the network, saving time and reducing human errors.

In this lesson, you’ll learn how to configure, verify, and troubleshoot DHCP step by step on a Cisco router, just like in real network environments.

Figure 1 – DHCP Configuration Topology

The first step is to exclude a range of IP addresses that won’t be assigned to DHCP clients. These reserved addresses are meant for important devices like servers, routers, or printers that always need static IPs.

The command is : ip dhcp excluded-address

R1(config)# ip dhcp excluded-address 192.168.1.1 192.168.1.10

This command ensures that the IP addresses from 192.168.1.1 to 192.168.1.10 are excluded from the DHCP pool. This avoids conflicts between dynamically assigned IP addresses by the DHCP server and the statically assigned IP addresses for critical devices.

To dynamically assign IP addresses to clients, you need to create a DHCP pool.

A DHCP pool is a named configuration that defines the settings for DHCP clients. It acts as a container where you specify the range of IP addresses that can be assigned, along with other parameters like the default gateway and DNS servers.

To create a DHCP pool, use the following command: ip dhcp pool

R1(config)# ip dhcp pool MY_DHCP_POOL

This command creates a DHCP pool named MY_DHCP_POOL and enters DHCP configuration mode, where you can define the network settings for DHCP clients.

Once the DHCP pool is created, you need to specify the network range from which IP addresses will be assigned. This tells the router which subnet is available for DHCP clients.

To create a DHCP pool, use the following command: network

R1(dhcp-config)# network 192.168.1.0 255.255.255.0

or using CIDR notation:

R1(dhcp-config)# network 192.168.1.0 /24

Figure 2 – DHCP Network Topology

This means the router can allocate IPs from 192.168.1.1 to 192.168.1.254, except for excluded addresses.

The default gateway is the IP address that devices use to send traffic outside their local network.

Configuring the default gateway ensures that DHCP clients can communicate with external networks.

R1(dhcp-config)# default-router 192.168.1.1

In this example, the router's IP address (192.168.1.1) is set as the default gateway for DHCP clients, allowing them to reach other networks.

The DNS server resolves domain names into IP addresses, allowing devices to access websites and network resources using names like google.com.

R1(dhcp-config)# dns-server 8.8.8.8

In this example, Google’s public DNS server (8.8.8.8) is used. You can also specify an internal DNS server if needed.