Why VLAN networks?


I am trying to put together a concise list of reasons to VLAN out a decent sized network.  While I know the advantages of VLANs, sometimes I have a hard time articulating them to clients or people who think they know everything and they have realtime and non-realtime apps running on a flat network.  Can anyone help out?
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JohnBusiness Consultant (Owner)Commented:
VLAN's add complexity. The simple reason to use them is to (a) separate two (or more) company networks on a single ISP feed and / or (b) to segregate a guest wireless network that cannot access a company network.

Otherwise there is not much need to use one. Avoid the complexity if you can.

... Thinkpads_User
Daniel HelgenbergerCommented:
They are the same for using virtual machines; better any virtualized stuff. If you can sell your client virtual machines rather than physical - which might be a lot easier to comprehend for them - you can sell them VLANs for the same reasons.

They both add complexity - but this is the only downside and true for a lot of stuff. But, the flexibility you get with them outweighs the disadvantage by far. How can you get a lot of networks to your VM's if not by VLANing? And, most of the hardware nowadays can do it for 'free'.
Also, it adds a lot of security. Ask if they want to provide Guest WAN access. There you have it. I deploy several VLANs even on relatively small networks. For some technologies like RADIUS/WPA-Enterprise you even need them.
Further you often need to separate Out Of Band Management and production networks. In medium- to larger networks not using VLANs will make things manageable in the long run.

Keep in mind, with the switches today there is not 'no VLAN' any more. They all use a default VLAN.
AkinsdNetwork AdministratorCommented:
Why would a school break 1 grade to many classes?

View those classes as vlans

1. 1st benefit
Ease of management
- limit broadcast, limit collisions, apply access list that affects only a group, allow access eg, a vlan can access internet, while others can't etc

2. Computers are chatty and send out lots of arp messages (broadcasts)
Vlans help keep broadcast messages within the VLAN local to them.
Cisco recommends maximum of 500 workstations per VLAN for this reason /23 network.

3. Isolation or security
eg. It is best practice to isolate accounting and management (together or separately), visitor's wifi, servers etc. The list is endless and depends totally on perspective. VOIP, Video etc need to be on separate vlan for best quality.
Vlans let you configure Quality of Service (QoS) with more flexibility.

You can put 2 computers per VLAN if you desire. How many rooms you create in your house is your prerogative depending on your goals.
Choose your design based on the 3 reasons I provided

If none of those matter to you, you can lump all networks into 1 vlan as long as they are less that 500 hosts, otherwise, your network speed will be hampered severely.

You can still achieve the aforementioned goals with 1 vlan .......................
You get the picture, I believe

Vlans are not complex if you understand the concept.
It is actually very very easy to configure
You are missing a LOT if you are not using vlans in an enterprise environment.

All the best

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ClearBlueTechnologiesAuthor Commented:
Thanks for the feedback!
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