Multiple vlans with same subnets

[Asfandyar70754]

Hello everyone

Hope you are doing good today,

Is it possible to use same subnet (for say 192.168.36.x) on multiple vlans and both vlans will be Data vlans.

I am using Cisco 3560 Switch.

[rasmus.elmholt]

If the VLAN is only setup as a L2 switch then it does not care what subnets are used on the different vlans.

But if you want to have the same subnet on different SVI on a L3 switch you need to take a look at VRF's.

[Reza Sharifi]

Hi,

You can but not common and with limitations. If you want to put say port 5, 6 in vlan 200, and port 7,8 in vlan 300, all in the same vlan (192.168.1.0/24)  you can as long as there is no layer-3 SVL for either vlans, because if you try to configure say 192.168.1.1/24 for vlan 100 and 192.168.1.2/24 for vlan 300, the switch will complain about the same subnet being configured on 2 different SVIs. So, to overcome this you want one subnet per vlan.

HTH

[Richard Burts]

We do not know much about the environment here. There might be some situations where we could get it to work. But in general the answer is that no it does not work to have several vlans (perhaps vlans 10 and 20) and to have the same IP subnet (192.168.36.x) on both vlans. Part of the issue, as mentioned in a previous response) is that you would not be able to configure vlan interfaces for both vlans if both are using the same subnet. The other part of the issue is that if a device in vlan 10 (perhaps at 192.168.36.10) wants to communicate with a device in vlan 20 (perhaps at 192.168.36.20) then the device will arp for the destination address. The arp request is a broadcast and will be forwarded to all devices in vlan 10. But it will not be forwarded to vlan 20 and so the destination device will not see the request. The source device gets no response to arp and therefore can not communicate.