CCNA study guide question

[seepy83]

A fried of mine gave me a study guide for the CCNA and I came across this multiple choice Question...I'm not sure that I agree with the answer. Looking for comments.

What are some of the characteristics of a typical VLAN found in a switched LAN? (Select all that apply)
(A) VLANs logically divide a switch into multiple, independent switches at Layer 2
(B) Trunk links can carry traffic for multiple VLANs.
(C) A VLAN can span multiple switches
(D) VLANs typically increase the number of switches needed
(E) VLAN implementation significantly increases traffic due to added trunking information
(F) VLANs typically decrease the number of switches needed.

My answer - A, B, C, F

Study Guide answer - A, B, C.

I don't agree that F is not correct. In order to achieve the same configuration that can be achieved from VLANs, without using VLANs, you would need to purcahase additional switches.

Anyone care to tell me why i'm wrong? Or if you also think the Study Guide is wrong?

Thanks

 

[jlazzaro]

under certain circumstances i can see where you're coming from, but the question is worded more so from a switchport perspective rather than overall network design.

the official (err, rather TestKing) answer:

The number of total switches needed in a network is the result of the number of devices on the entire LAN that need to be connected. Whether VLANs are used or not will have little, if any, impact on the total number of switches needed in a LAN.

 

[spidey07]

Not to mention you can assume any switch from Cisco will have vlan functionality.

It's kind of a trick question because of D and F, it looks like they want you to pick one position when it really has zero impact.

 

[Pheran]

Seepy, I can see where you are coming from if you are assuming that the starting point is unmanaged switches. I think the question is poorly constructed and could be interpreted either way. As long as you understand the concept, and it seems that you do, you should do fine on the actual exam.

 

[seepy83]

Thanks for the comments.

Spidey - I think the fact that all switches from Cisco support VLANs is really the only good argument for it not being a correct answer.

Definitely a poorly worded question and I hope the real exam is less ambiguous. If I had that question on the exam I definitely wouldn't answer any differently than I did...

 

[drebo]

Well, technically, even if not every Cisco switch supported VLANs, it still wouldn't necessarily increase the number of switches needed. You can run multiple layer 3 networks over the same layer two network. It's an ARP nightmare, but you don't need to logically divide the layer 2 network in order to logically divide the layer 3 network. Now, I'm not saying I'd ever set something up like this, but the fact that you can invalidates F as a correct answer under any circumstances.

 

[seepy83]

Originally posted by: drebo
Well, technically, even if not every Cisco switch supported VLANs, it still wouldn't necessarily increase the number of switches needed. You can run multiple layer 3 networks over the same layer two network. It's an ARP nightmare, but you don't need to logically divide the layer 2 network in order to logically divide the layer 3 network. Now, I'm not saying I'd ever set something up like this, but the fact that you can invalidates F as a correct answer under any circumstances.

VLANs create different Broadcast Domains. The only way to achieve that without using VLANs is to use a different switch for each subnet.

 

[drebo]

I'm aware of that, but that's not what the question asked. Different broadcast domains are not a necessity for separating LAN traffic. While I'd agree that they're an excellent idea, they're not technically needed. Multiple layer 3 networks can run over a single layer 2 segment without VLANs. It's not a good idea, but it's possible. As such, F cannot be a correct answer.

If I have 20 devices that I want to be in 20 different layer 3 networks and I don't have a managed switch, I can still do that with a single 24 port switch. It's a horrible idea, but it is possible.