Lab 34: DHCP Relay

Lab Objective:

The objective of this lab exercise is for you to learn and understand how Cisco IOS routers forward DHCP requests to remote DHCP servers.

Lab Purpose:

Configuring Cisco IOS routers to forward DHCP requests to remote DHCP servers is a fundamental skill. In some cases, DHCP servers are located in a central location (such as the Headquarters) and DHCP requests from local clients need to be forwarded on to these servers. By default, Cisco IOS routers do not forward broadcast traffic. Therefore (because DHCP requests are broadcast packets), configuration is required on the Cisco IOS devices to forward these broadcasts to the DHCP servers. As a Cisco engineer, as well as in the Cisco CCNA exam, you will be expected to know how to configure Cisco IOS routers to forward DHCP requests to remote DHCP servers.

Certification Level:

This lab is suitable for CCENT and CCNA certification exam preparation.

Lab Difficulty:

This lab has a difficulty rating of 5/10.

Readiness Assessment:

When you are ready for your certification exam, you should complete this lab in no more than 10 minutes.

IMPORTANT NOTE: In order to test DHCP functionality, you will need a workstation DHCP client configured to receive IP addressing information via DHCP. If you do not have a DHCP client, feel free to substitute it with another Cisco IOS router configured as a DHCP client as illustrated in the previous lab.

Lab Topology:

Please use the following topology to complete this lab exercise:

Lab 34: DHCP Relay 3

Task 1:

Configure the hostnames on R1, R2, and Sw1 as illustrated in the topology.

Task 2:

Configure R1 to provide clocking information for R2 at a speed of 256 Kbps. Configure the IP addresses on R1 and R2 S0/0 interface as illustrated in the topology.

Task 3:

Configure VLAN300 named DHCP_VLAN on Sw1. Assign the FastEthernet0/2 and FastEthernet0/3 interfaces on Sw1 to this VLAN. Ensure that the ports immediately transition to the Spanning Tree Forwarding state.

Task 4:

Configure R2 as a Cisco IOS DHCP server with the following settings:

  • DHCP pool name: REMOTE-DHCP-POOL
  • DHCP network:
  • DNS server:
  • WINS server:
  • Default gateway:
  • DHCP lease time: 8 days

You will need to add a static route to the 10 network on R2 because it will otherwise drop any traffic not listed in its routing table.

Task 5:

Configure R1 to forward DHCP requests from DHCP clients connected to F0/0 to R2 (the IOS DHCP server).

Task 6:

Verify your DHCP configuration on the connected workstation (or other DHCP client), and also verify that your Cisco IOS DHCP server is showing a leased DHCP address.

Configuration and Verification

Task 1:

For reference information on configuring hostnames, please refer to earlier labs.

Task 2:

For reference information on configuring DCE clocking and IP addressing, please refer to earlier labs.

Task 3:

Sw1#config t 
Enter configuration commands, one per line.  End with CTRL/Z. 
Sw1(config)#vtp mode transparent 
Setting device to VTP TRANSPARENT mode. 
Sw1(config-vlan)#name DHCP_VLAN 
Sw1(config)#interface range fastethernet0/2 – 3 
Sw1(config-if-range)#switchport mode access 
Sw1(config-if-range switchport access vlan300 
Sw1(config-if-range)#spanning-tree portfast 
%Warning: portfast should only be enabled on ports connected to a single host. Connecting hubs,
 concentrators, switches, bridges, etc... to this interface when portfast is enabled, can cause
 temporary bridging loops. 
Use with CAUTION 
%Portfast will be configured in 2 interfaces due to the range command but will only have effect
 when the interfaces are in a non-trunking mode. 
Sw1(config-if-range)#no shutdown 

Task 4:

R2#config term 
Enter configuration commands, one per line.  End with CRTL/Z.
R2(config)#ip dhcp pool REMOTE-DHCP-POOL 
R2(dhcp-config)#network /24 
R2(dhcp-config)#lease 8 
R2(config)#ip dhcp excluded-address 
R2(config)#ip route s0/0 

Task 5:

R1#conf t 
Enter configuration commands, one per line.  End with CRTL/Z. 
R1(config)#int fastethernet0/0 
R1(config-if)#ip helper-address 

NOTE: The ip helper-address command is used to point an interface connected to a subnet with DHCP clients to a remote DHCP server. You can specify more than one DHCP server with this command; however, the first one configured will always be tried first.

Task 6:

R2#show ip dhcp pool REMOTE-DHCP-POOL 

Utilization mark (high/low)    : 100 / 0 
Subnet size (first/next)       : 0 / 0 
Total addresses                : 254 
Leased addresses               : 1 
Pending event                  : none 
1 subnet is currently in the pool : 
Current index    IP address range                    Leased addresses                 1

R2#show ip dhcp binding 
Bindings from all pools not associated with VRF: 
IP address       Client-ID/          Lease expiration        Type Hardware address/ User name         0100.1d09.d402.38   Mar 09 2017 04:27 AM    Automatic

Lab 34: DHCP Relay 4

NOTE: If you decided to use another Cisco IOS device as a DHCP client, you will need to add the command below to the FastEthernet interface:

R3(config-if)#ip address dhcp 
R3(config-if)#no shut 
*Mar  1 00:04:55.603: %LINK-3-UPDOWN: Interface FastEthernet0/0, changed state to up
*Mar  1 00:04:56.603: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/0, changed state to up 
*Mar  1 00:05:07.375: %DHCP-6-ADDRESS_ASSIGN: Interface FastEthernet0/0 assigned DHCP address, mask, hostname R3

You can check your DHCP configuration by issuing the show dhcp server command (if you are using a router as a host) as illustrated in the following output:

R4#show dhcp server 
DHCP server: ANY ( 
Leases:   3 
Offers:   3      Requests: 3     Acks: 3     Naks: 0 
Declines: 0      Releases: 6     Bad:  0 
DNS0:,   DNS1: 
NBNS0:,   NBNS1: 
Subnet:   DNS Domain:
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