Local VLANs

Local VLANs
Unlike an end-to-end VLAN, a
local VLAN
is configured by physical location and not by function,
project, department, and so on. Local VLANs are used in corporations that have centralized
server and mainframe blocks because end-to-end VLANs are difficult to maintain in this
situation. In other words, when the 80/20 rule becomes the 20/80 rule, end-to-end VLANs are
more difficult to maintain, so you will want to use a local VLAN.
In contrast to end-to-end VLANs, local VLANs are configured by geographic location; these
locations can be a building or just a closet in a building, depending on switch size. Geographically
configured VLANs are designed around the fact that the business or corporation is using
centralized resources, such as a server farm. The users will spend most of their time utilizing
these centralized resources and 20 percent or less on the local VLAN. From what you have read
in this book so far, you must be thinking that 80 percent of the traffic is crossing a layer 3 device.
That doesn’t sound efficient, does it?
Because many modern applications are not very tolerant of delay (a bit like users), you must
design a geographic VLAN with a fast layer 3 device (or devices) for interconnecting your VLANs
and for general site-to-site connectivity. Fortunately, layer 3 devices themselves are becoming
faster. The benefit of this design is that it will give the users a predetermined, consistent method
of getting to resources. But you cannot create this design with a lower end layer 3 model. In the
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Chapter 14 
VLANs, Trunks, and VTP
past, these network types were only possible in large corporations with plenty of spending power,
but as technology develops, the price is going down.