User VLAN Do Not Acquire DHCP Address

When configuring VLANs on a layer 3 Cisco switch we often tend to segment our network by grouping devices in certain VLANs for security/departmental/geographical purposes.

Enabling inter-VLAN routing allows all the devices on different VLANs to communicate with each other.

If you’ve placed DHCP devices on a VLAN separate from the DHCP server you’ll notice that those devices will not receive an IP address.

For example, your DHCP server is on VLAN 2 and your users are on VLAN 3. To allow your users’ computers to acquire an IP address from the DHCP server on VLAN 2 you’ll have to configure the ip helper-address command on VLAN 3:

Enter VLAN 3 interface configuration

conf t
int vlan 3

configure the ip helper-address command to point to your DHCP server

ip helper-address 192.168.1.5
exit

When the DHCP devices on VLAN 3 send a broadcast over the network for DHCP, VLAN 3 will forward this request to 192.168.1.5. Be sure to replace 192.168.1.5 with your own DHCP server.

Related posts:

1. How To Configure a Router-on-a-Stick
2. 5 Easy Steps to Securing Your Cisco Switch or Router
3. Virtual LANs Notes