Understanding the network.pdf - Back to Home

need. This method not only allocates the Layer 2 bandwidth in a more
efficient manner, but also enhances network security by allowing
hosts to see only the Layer 3 traffic they need to see.
VLAN Usefulness
Although proprietary (and now standards-based) VLAN capability has
been part of many switch manufacturers'feature sets for years, the
implementation of VLANs has not become as prevalent as the
implementing of "plain vanilla" Layer 2 switching. There are three
main reasons for this.
The first reason is the complexity of using distributed VLANs.
Deploying VLANs properly requires planning and, in many cases,
major network redesign. When switching hit the marketplace, many
manufacturers pushed Layer 2 switches as the panacea for large,
congested, Layer 3 segmented networks. "Get rid of your routers,
flatten your network," was their sales pitch. What most customers
missed was that in order to correctly implement this idea, they
needed to replace their shared networks with switched networks. Well,
an entire switched network is quite expensive, but the idea sounded
good. So, they bought some switches, attached multiport repeaters
and MAUs to them, and then flattened their networks. For many, this
resulted in networks with excessively large broadcast domains, with
40 percent of the network traffic being utilized for network broadcasts.
So, when the same vendors came around a few years later and
started talking about reducing broadcast domains and using multiport
routers to manage multiple "virtual" Layer 3 networks, they got their
hats handed to them.
The second reason VLANs are not as prevalent is that standards
migration only affected those who really kept up on the evolving
technology. Until the IEEE 802.1q standard was released, network
administrators were forced to use only a single vendor's switching
implementation, for compatibility reasons. Large-scale enterprise
network administrators tend to keep away from non-standards-based
solutions unless they have no other choice. Therefore, with no
standards, no cross-vendor compatibility, and no real enhancement
to the network that could not be achieved by other means, VLANs did
not catch on with the individuals who could have really used them.
Now, with standards-based VLANs available, utilization is starting to
become more common, particularly in high bandwidth/speed data
farms in WWW and database application services.