Can also be a DHCP client

As a DHCP server, a Cisco router not only automatically assigns IP addresses to PCs and other devices, but can also be configured as a DHCP client. For example, if you have an Internet connection service and your ISP assigns you an IP address via DHCP, configure your Cisco router as a DHCP client.

Figure: Example of making a Cisco router a DHCP client
Figure: Example of making a Cisco router a DHCP client

Related articles

The details for configuring a Cisco router as a “DHCP server” are described in the following article.

N-Study
Cisco IOS DHCP Server Configuration and Verification Commands | N-Study
https://www.n-study.com/en/tcp-ip/cisco-ios-dhcp-server-configuration/
You can use a Cisco router as a DHCP server to distribute IP addresses to DHCP clients.This section describes the configuration and verification commands to make a Cisco router (Cisco IOS) act as a DHCP server.

N-Study
Cisco Router DHCP Server Configuration Example | N-Study
https://www.n-study.com/en/tcp-ip/cisco-dhcp-server-configuration-example/
Configure the Cisco router as a DHCP server; configure a DHCP relay agent and manual binding to assign a specific IP address.

DHCP Client Configuration

To automatically assign an IP address/subnet mask for an interface with a Cisco router as a DHCP client, use the following command in interface configuration mode.

IP address configuration DHCP Client

(config)#interface <interface-name>
(config-if)#ip address dhcp

<interface-name> : Interface name to be a DHCP client

The router connecting to the Internet must also be configured with a default route. In most cases, the default route is configured as a static route.

To use the IP address of the default gateway obtained by DHCP as the next hop for the default route, make the following configuration

Default route with DHCP default gateway as next hop

(config)#ip route 0.0.0.0 0.0.0.0 dhcp

Client ID

There is a client ID to identify the DHCP client; the default client ID for the ip address dhcp command is a string like this

“cisco-<MAC-address>-<interface-name>”

To make the client ID the MAC address of the interface, add the client-id option to the ip address dhcp command.

IP address configuartion DHCP Client Change Client ID

(config)#interface <interface-name>
(config-if)#ip address dhcp client-id <interface-name>

<interface-name> : Interface name to be a DHCP client

With the client-id option, the client ID is the MAC address of the interface. It is a hexadecimal number, not a string.

<MAC-address>

release/renew

To release the IP address/subnet mask assigned by DHCP, enter the following command in privileged EXEC mode

DHCP Release

#release dhcp <interface-name>

<interface-name> : Interface name configured as DHCP client

Also, if you want to reacquire the address via DHCP, use the following command in privileged EXEC mode.

DHCP Renew

#renew dhcp <interface-name>

<interface-name> : Interface name configured as DHCP client

DHCP Client Verification

As a DHCP client, use the following command to verify IP address and other assignments.

CommandsOverview
#show ip interfaceVerify detailed information at the Layer 3 level for the interface.
#show dchp leaseVerify the information assigned by DHCP.
Table: DHCP Client Verification commands

DHCP Client Configuration Example

Configure R1 in the following figure as a DHCP client.

Figure: Example of DHCP Client Configuration
Figure: Example of DHCP Client Configuration
  • Obtain the IP address/subnet mask of R1 Fa0/0 via DHCP.
  • Configure the default route as a static route on R1.

R1 DHCP Client Configuartion

Use the ip address dhcp command to make Fa0/0 on R1 a DHCP client. Also, specify dhcp as the next hop for the default route “0.0.0.0 0.0 0.0.0” in the static route configuration.

R1 DHCP Client Configuration

interface FastEthernet0/0
 ip address dhcp
!
ip route 0.0.0.0 0.0.0.0 dhcp

R1 DHCP Client Verification

The show ip interface fa0/0 shows that the IP address and subnet mask are assigned by DHCP.

R1 DHCP Client Verification show ip interface

R1#show ip interface FastEthernet 0/0
FastEthernet0/0 is up, line protocol is up
  Internet address is 10.0.0.2/24
  Broadcast address is 255.255.255.255
  Address determined by DHCP
  MTU is 1500 bytes
  Helper address is not set
-- omitted --

The show dhcp lease command shows the TCP/IP configuration information assigned by the DHCP server.

R1 DHCP Client Verification show dhcp lease

R1#show dhcp lease
Temp IP addr: 10.0.0.2  for peer on Interface: FastEthernet0/0
Temp  sub net mask: 255.255.255.0
   DHCP Lease server: 10.0.0.100, state: 3 Bound
   DHCP transaction id: 16EB
   Lease: 86400 secs,  Renewal: 43200 secs,  Rebind: 75600 secs
Temp default-gateway addr: 10.0.0.100
   Next timer fires after: 11:53:45
   Retry count: 0   Client-ID: cisco-cc01.20f4.0000-Fa0/0
   Client-ID hex dump: 636973636F2D636330312E323066342E
                       303030302D4661302F30
   Hostname: R1

In addition, a default route is registered in the routing table of R1 with the default gateway obtained by DHCP as the next hop.

R1 DHCP Client Verification show ip route

R1#show ip route
-- omitted --

Gateway of last resort is 10.0.0.100 to network 0.0.0.0

     10.0.0.0/24 is subnetted, 1 subnets
C       10.0.0.0 is directly connected, FastEthernet0/0
C    192.168.1.0/24 is directly connected, FastEthernet1/0
S*   0.0.0.0/0 [1/0] via 10.0.0.100

IP Addressing