Introduction to multi-vlan dhcp service settings

We all know that DHCP is a service for IP address management. In some network changes, we also need to modify the settings. Here we will explain how to configure the multi-vlan dhcp service. All aspects must be taken into account when upgrading the network, and how to implement the DHCP service in a multi-VLAN environment is one of them.

Multi-vlan dhcp service settings: Principles

To obtain IP addresses using DHCP, broadcast packets are required. Normally, DHCP can only be implemented in the same broadcast domain. The VLAN is created to isolate broadcast packets. Why can DHCP cross-network segments be implemented on layer-3 switches? This requires us to convert the broadcast packet of the DHCP request into a unicast request, and then forward the request to the VLAN of the DHCP server through a layer-3 route, so as to implement the cross-vlan dhcp service.

Multi-vlan dhcp service settings: Implementation Method

To implement the cross-vlan dhcp service, you must specify the IP address of the DHCP server on the vswitch and create a new scope on the DHCP server.

The following describes how to use Catlyst 4506 of Cisco as an example:

1. Configure the DHCP server on the vswitch:

Ip dhcp-server 192.168.0.69

2. Set the IP address of the same DHCP server for each VLAN in the vswitch:

Interface Vlan11

Ip address 192.168.1.254 255.255.255.0

Ip helper-address 192.168.0.69 DHCP Server IP

Interface Vlan12

Ip address 192.168.2.254 255.255.255.0

Ip helper-address 192.168.0.69 DHCP Server IP

3. On the DHCP server, set the network addresses to 192.168.1.0 and 192.168.2.0 respectively, and set the "Router" option of these scopes to the interface IP address of the corresponding VLAN.

The preceding operations are related to the multi-vlan dhcp service settings. Hope you can master it.