How to Setup DHCP for Multiple VLANs

This tutorial shows how to setup DHCP for multiple vlans.

DHCP Servers are used for allocating dynamic IP addresses to users on the network. In a multi vlan environment, where there are multiple networks, DHCP servers are configured with multiple scopes, which would provide IP addresses to users on the vlans with respective IP address.

The DHCP servers are setup and configured on a specific vlan. Users belonging to other vlans, would contact the DHCP server through a feature called IP Helper address available on routers. DHCP clients on other vlans would be unable to reach DHCP servers which are configured on different networks or vlans, due to which the IP helper address feature is used. The feature is used on the sub interface of the vlan in which the DHCP clients reside and would point to the IP address of the DHCP Server.

How to setup DHCP for Multiple VLAN

In the above topology, the DHCP server is configured on VLAN 3. There are two scopes on the DHCP Server, which would provide IP address in the range to VLAN 2 and to VLAN 3. For users in VLAN 2 to contact the DHCP Server in VLAN 3, the IP Helper address feature is used.

The details of the configuration are shown below.
router(config)#interface fastethernet 0/0.1 (VLAN 2 Sub interface )
router(config-if)#ip helper-address (IP address of DHCP Server)

This is a sample content from the book – VLAN Network Design

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