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Home > Forums > Communications Rack > Networking > Cisco: Switches Forum

Multiple vlans using same subnet

Read More Threads Like This One

Jeilaanni (TechnicalUser)

27 Jun 12 1:22

Hello,

Is it possible that multiple vlan using same subnet? Here is an example

switch 1: port 1 to 5 having vlan 11
switch 2: port 1 to 5 having vlan 3922

what are the required configuration to make the switch 1: port 1 to 5 able to communicate to switch 2: port 1 to 5 using same subnet ip address?

Carpua (ISP)

27 Jun 12 4:32

hi

You need a layer 3 device to do the routing between the Vlans. it can be a router or a mulyi-layer switch

chieftan (MIS)

27 Jun 12 10:04

He is asking about having 2 different VLAN's on the same subnet.

Carpua's response is correct if you are utilising different subnets for the VLAN's.

As far as I am aware, you cannot have 2 VLANs on the same subnet, that would completely defeat the purpose of VLANs (Security and Broadcasts).

unclerico (IS/IT--Management)

27 Jun 12 13:13

it is generally a best practice to have a 1-to-1 relationship between VLAN and subnet; however, it can be done where two VLANs reference the same subnet. chieftan hit it right on the head, there is no point in doing what you are proposing as you lose all of the benefits that VLANs provide.

VinceWhirlwind (TechnicalUser)

28 Jun 12 0:46

You can do that if you bridge the VLANs between Switch1 and Switch2.
ie, the Switch1 uplink interface is "Switchport mode access/switchport access vlan 11" & the Switch2 uplink interface is "Switchport mode access/switchport access vlan 3922".

You should provide us with more context explaining why you have this request.

Unless you have a *really* good reason, then follow UncleRico's "1-to-1 relationship" advice.

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