From the last CCNA Tutorial, we have configured router’s interface ip address and subnet mask. Client hosts must have its own ip address to complete the network. With this, we manually assigned a static ip address to each and every hosts within the network. Thus, it would be time consuming if we are to maintain a medium to a large scale network.

It would simply be easy if DHCP service is enabled on the router. DHCP is a router service which handles all dynamic IP address assignments to every DHCP enabled  devices existing in the network. As a general rule, only shared devices, like printers, servers, routers, and switches needs a static ip address. All other devices should use DHCP-assigned IP addresses.

Cisco CCNA Video Tutorial: Cisco Router DHCP Configuration

For students and beginners, I recommend you read some of the basics in Cisco CCNA Tutorials and Practice Exams

For static ip configuration, refer to configure lan interface static ip addressing

Download Packet Tracer Practice Problem: DHCP Cisco Router Configuration

Note: Available video tutorial on Cisco Router DHCP Configuration

Steps to configure a DHCP Service in a Cisco Routers

1. Specify the DHCP Pool Name

In the global configuration mode, execute ip dhcp pool <pool name> to define a DHCP Pool Name which places you in dhcp pool configuration mode. As the dhcp configuration started, the prompt changes to (dhcp-config). DHCP pool naming is required in order to define and track multiple DHCP pools.

In this example, myLAN is the DHCP pool name from the command ip dhcp pool myLAN.

2. Specify the DHCP Network Address

We will be using Class C private ip address with its network address 192.168.0.0 and the subnet mask of 255.255.255.0. You may also use classless ip address (some uses this for multiple subnets).

The proper format for setting up network address in DHCP is network <network address> <subnet mask>. In this example, network 192.168.0.0 255.255.255.0.

3. Specify the Networks Domain Name (not available in packet tracer)

DHCP specifies the domain name your network hosts belongs to. We don’t have a registered domain name (such as bitsbyjohn.com), a local name such as .lan or .local can be used. We will use mydomain.local as domain name.

To set this up, the command domain-name <domain-name> is used. So, domain-name mydomain.lan specifies the domain name for DHCP clients.

4. Specify the Default Gateway

To access the external network, the default gateway should be specified. This can be set up through a command default-router <ip address>. In this exercise, we will be using the routers lan interface address. Using the command default-router 192.168.0.1 will specify any network clients to use 192.168.0.1 as the default gateway whenever the client users access to internet or external network.

5. Specify the DNS Server(s)

The Domain Name System most commonly known as the DNS is a service that looks for the ip address of the network hosts. The DNS Server holds the information of the hosts the returns the IP address. For example, a user browsed this site (www.bitsbyjohn.com) using Internet Explorer browser, the client’s computer asks the DNS server for the equivalent IP address for the bitsbyjohn.com web server (a computer that holds all website contents of the bitsbyjohn.com). In return, the DNS server replies the ip address of the bitsbyjohn.com web server.

In this exercise, we will assume that the dns server for lan is 192.168.0.2. (take note that the dns server ip address might came from your Internet Service Provider). To specify the dns addresses, use the format dns-server <ip address1> <ip address2>. Therefore, setting the dns server should be dns-server 192.168.0.2.

6. Specify WINS Server (not available in packet tracer)

Microsoft WINS (Windows Internet Name Service ) Server provides naming resolution if the query is not found in the DNS namespace.

To specify the WINS server, use the command netbios-name-server <WINS Server IP address>. In this example, assuming the WINS server holds the ip address of 192.168.0.3. Using netbios-name-server 192.168.0.3 appends WINS server address to clients. This setup is optional. If no server exists, this can be skipped.

7. Specify Lease Time for DHCP (not available in packet tracer)

The lease specifies how long the hosts may keep the DHCP assigned ip address. The command lease <days> <hours> <minutes> specifies until when the hosts will preserve the assigned ip address, after that period, the host will asks the dhcp server to keep that ip address or lease for another one.

To specify lease time of 2 hours, use the command lease 0 2 0 from the command line interface.

8. Specify DHCP Excluded IP Address Range

This line specifies the range of ip addresses that will not be leased by the cisco router. These ip addresses that belongs to the servers, printers, routers and switches which are manually assigned.

To specify the range, use ip dhcp excluded-address <starting ip address> <ending ip address>. In this exercise, ip dhcp excluded-address 192.168.0.1 192.168.0.5 was used.

9. Check the DHCP Server and Clients

From the command prompt in the client computers, verify the ip configuration by sending ipconfig (make sure that the client is configured to receive ip address from dhcp server).

To check the status of the DHCP Server, use the command show ip dhcp bind from the router’s command line interface.

Command Summary: Configuring DHCP Server in Cisco Router using Packet Tracer

Lab-R1> ena

Lab-R1# config t

Lab-R1(config)# ip dhcp pool myLAN

Lab-R1(dhcp-config)# network 192.168.0.0 255.255.255.0

Lab-R1(dhcp-config)# domain-name mydomain.lan

Lab-R1(dhcp-config)# default-router 192.168.0.1

Lab-R1(dhcp-config)# dns-server 192.168.0.2

Lab-R1(dhcp-config)# netbios-name-server 192.168.0.3

Lab-R1(dhcp-config)# lease 0 2 0

Lab-R1(dhcp-config)# exit

Lab-R1(config)# ip dhcp excluded-address 192.168.0.1 192.168.0.2