December 12, 2000, 2:15 PM — Simulators are all the rage these days. There are flight simulators, driving
simulators, city simulators -- and you and I have network simulators.
Although the first items I listed are diversions for most, network simulators are
serious business and can come with a serious price tag -- as much as $30,000. That's
certainly not pocket change, but it can be cheap compared to the cost of building a
prototype network using real hardware or implementing a new design on a production
Network simulation packages let you model enterprise network topologies and
enterprise applications. You can use them to estimate a network's performance and
capacity. They allow you to create what-if scenarios, which can be useful in
provisioning bandwidth and adding new network devices such as switches and routers.
If a simulator can accurately model a production network, it solves a quandary
confronting network architects and operators. Testing new equipment or designs on a
live production network is never advisable. On some networks, mission-critical
applications run 24 hours a day, seven days a week, and you don't want to be testing
when someone is depending on the network. Testing can result in short-term or (perish
the thought) long-term outages.
As a result, new designs are often relegated to a test network that tries, with
varying degrees of success, to replicate the production network. A scenario may work
just fine on the test network, but may collapse when moved to the production
Network simulators offer a way around this dilemma. Simulators use mathematical
models with a GUI front end. Most contain templates that model network devices,
including the interfaces you have on the real network and the infrastructure that
connects them. If the model is accurate, you can create networks that are good
simulations of your actual network. New designs and concepts can be safely modeled
using network simulators without endangering the actual network.
Many network simulators will automatically discover and import the devices and
topology of the production network, though not necessarily the traffic level. You can
specify traffic levels to test on the various simulated segments.
However, importing a snapshot view of the network may not always be a practical
approach. One reason is that networks are never static. From the time a model is
imported to the time a scenario is ready for testing, the network may have undergone
major changes in infrastructure or traffic flow. But an even more important reason to
avoid the import function is that it's not always as accurate as the vendors allege.