I have the following configuration: enter image description here I would like to provide every host from VLAN_101 with DHCP-provided IP addresses. There are two DHCP servers running - one grants adresses for every host below switch LAN_1 and the other one - below LAN_2. What can I do, except from turning one DHCP server off, to make hosts in VLAN_101 be in a single subnet? Is this manner correct? If not, what should I change to make it genuine? Any advices are welcome.

  • You can make another VLAN, e.g. 102, and put LAN_2 hosts in this VLAN. And then reconfigure your DHCP for new VLAN. Nov 30, 2017 at 15:03
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2 Answers 2


In your topology the host in VLAN 101 connected to switch LAN_2 are in a separate network that those connected to switch LAN_1. This is because you have a router between them.
So you have 2 distinct VLAN 101, which could be very confusing.

I strongly suggest you change the VLAN name for one of them.

Apart this, you have nothing special to do to provide different DHCP on those networks, since they are totally independent.


You can use one DHCP server for both LANs, but you need to put in a DHCP relay in the router. For Cisco devices, that is the ip helper-address command. You place it on the interface of the LAN without the DHCP server, and you configure scopes for both LANs on the one DHCP server.

Assume that the DHCP server is on LAN_1 at and that LAN_2 is connected to the router on interface FastEthernet0/2. Your DHCP relay would look something like this on R1:

interface FastEthernet0/2
  ip helper-address

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