5

What are the disadvantages of VLAN?

Whereas advantages are : Broadcast Control, Security and Fexibility

3

I think, managment is a little more complex, nothing out of this world, but, you need to make sure wich ports do you configured like access, and vlans permitted on trunk ports. This one is only done on the firs time, the you only need to permits vlans and configure the access for machines who needs to communicate.

The other thing is when you need to add a new vlan, you need to configured on all the switches on your networks, or configure VTP, a little more complex too.

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  • I think which interoperability can be a problem, don't you? – TMoraes Oct 26 '15 at 21:25
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    You are rigth, interoperability can be a problem, with the configuration of how one vlan can conmunicate with other, configuring on the router the vlan interfaces, or the gateway of that vlan, or a router on a stick, with the encapsulation dot1q. But, once you configured that, conf never be a origin of troubles, – Orlando Gaetano Oct 27 '15 at 18:27
4

They are a tool. like any other, and can be misapplied, like any other.

It's not infrequently the case that someone (possibly in management) will get all excited about VLANs and proceed to break (or order broken) a network by deploying VLANs willy-nilly, ignoring the need of various devices on the network to actually communicate over the network. With proper planning these needs can be met via inter-VLAN-routing, but proper planning is often engaged in only after the network suddenly stops working...

A common enough example is VLAN-ing a guest wireless network. A common enough result (entirely avoidable with planning) is that the guest wireless network ends up without a DHCP server or a route to the internet, because it's successfully "isolated" but the fact that this now means it's an entirely separate network that needs every service any network needs to function is neglected. Blame is then applied with a broad brush to the wireless AP vendor, who has nothing to do with the actual problem, but makes a handy target since the issue is with a wireless network not working.

As with many things, poor documentation can make a VLAN setup that actually worked fine when set up fall apart when details are forgotten, employees move on or forget details that are not documented, and some seemingly irrelevant change balkanizes a VLAN.

Implemented properly, these things don't happen. They happen commonly enough to suggest that proper implementation is not as common as it should be.

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