Introducing Network Design Concepts Avoiding Failures The network architect

Document Sample
Introducing Network Design Concepts Avoiding Failures The network architect Powered By Docstoc
					Avoiding Failures

The network architect should try to deliver a network that is unaffected
by failures and can recover fast in the event of a catastrophe. Core
Cisco routers and switches can have dual power supplies and fans, modular
chassis-based design as well as additional management components.

Redundant modules increase the cost of ownership, but they are typically
well worth the investment. It is a good practice for the Core layer
switches to have hot-swappable units whenever possible. Hot-swappable
units can be installed or detached without first having to turn off the
power to the switch. Using these devices decreases repair time and
problems to network services.

Larger corporations frequently install generators and big UPS devices.
These UPS devices stop small power outages from causing big network

Decreasing Human Error

Human mistakes contribute to network disasters. Unfortunately, adding
redundant links and network appliances cannot eradicate these factors.
Many network disasters are the outcome of poorly designed networks or
inappropriate new equipment. You should never make any change on a
production environment before first testing it in a lab environment!

Disasters at the Core Layer can cause extensive outages. It is very
important to have policies and procedures that describe how modifications
are approved, tested and installed. Create a back-out strategy to return
the systems to the previous state if changes are not as expected.

The appropriate routing protocol for the Core Layer is determined by the
scope of the network and the amount of redundant links that are
available. A key factor in choosing a routing protocol is how fast it
adjusts from a device failure.


Network convergence happens when all routers have comprehensive and
precise information about the network. When the convergence time is fast,
a network can react very quickly to a change in topology. Elements that
influence convergence time include: 1. the speed at which the routing
updates replicate in the network, 2. the time that it takes each router
to do the calculation to determine the best routes.

Picking a Routing Protocol

Many dynamic routing protocols provide tolerable convergence times in
small networks. In big networks, protocols like RIPv2 converge very
slowly and cannot prevent disruption of network services when a link
breaks. Usually, in a big enterprise network, EIGRP or OSPF offer the
most reliable routing solution.

Design Thoughts
Many networks use a mixture of dynamic and static routes. Network
architects should always consider the amount of routes required to
guarantee that all destinations in the network topology are accessible.
Long routing tables need substantial time to converge. Finally, the
network addressing scheme can seriously affect how well the routing
protocol can react to a disaster.

Manolis Skoras is a Cisco, Microsoft and HP Certified Trainer and
systems-network engineer. Recently he created a How To Pass CCNA exam
website to help his students and people around the world to better
understand the material they will be tested on, thus having greater
success rates. Check Certify4Sure today!

Shared By: