what is a vlan

[ilpadrino]

I know this sounds stupid. I know how to configure the vlan and can identify my vlans, but I haven't found a good explanation of the purpose of a vlan. Can anyone explain to me why you would want to use a vlan?

Thanks.

 

[BuckWeet]

Basically a VLAN is a way to logically seperate traffic on a switch. This way if you had users that had to have data secure against other normal data traffic you could do this. The way to get between VLAN's is via a Layer 3 box that can participate among the multiple vlans. Its also good for if you doing a IP Telephony application. You would seperate the voice traffic from the data traffic to keep the QoS up to the max possible.


BuckWeet

 

[ilpadrino]

so workstations on different vlan's would not be able to communicate? in a basic LAN configuration, where workstations all accessed a few servers, there would be no need for a vlan.

suppose you had 2 vlans, how would they access the internet that came in on the same switch?

 

[oj88]

VLANs are typically used to divide broadcast domains. We all know that broadcasts are part of the ethernet and TCP/IP standards and is used for ARP and DHCP, to name a few. Imagine having 200 or so users sharing a single broadcast domain (single VLAN), each broadcasting every few seconds. Even a 100Mbps LAN would easily be saturated on peak hours. Dividing the LAN into, say, four VLANs of about 50 users each, would lead to a more efficient use of bandwidth because broadcasts are never propagated beyond the VLAN it originated from. The downside is, you need some way to route traffic between VLANs. These days, inter-VLAN routing is easily done using Layer-3 switches.

Orlando Palomar Jr
CCIE# 11206, CCNP
CIPT Operations Specialist
Phil-Data Business Systems, Inc.

 

[Twinmoon]

As I understand them, Vlans a logical LANs using a physical LAN. Else oj88 and BuckWeet are right.

Also, by going though a layer 3 device, you can prevent the R&D from getting out to unsecure areas via access-lists.