1.2 Key Characteristics of Scalable Internetworks
1.2.1  Five characteristics of a scalable network
Although every large internetwork has unique features, all scalable networks have essential attributes in common. A scalable network has five key characteristics:
  • Reliable and available - A reliable network should be dependable and available 24 hours a day, 7 days a week. In addition, failures need to be isolated, and recovery must be invisible to the end user.
  • Responsive - A responsive network should provide Quality of Service (QoS) for various applications and protocols without affecting a response at the desktop. For example, the internetwork must be capable of responding to latency issues common for Systems Network Architecture (SNA) traffic but still allow for the routing of desktop traffic, such as Internetwork Packet Exchange (IPX), without compromising QoS requirements.
  • Efficient - Large internetworks must optimize the use of resources, especially bandwidth. Reducing the amount of overhead traffic, such as unnecessary broadcasts, service location, and routing updates, results in an increase in data throughput without increasing the cost of hardware or the need for additional WAN services.
  • Adaptable - An adaptable network is capable of accommodating disparate protocols, applications, and hardware technologies.
  • Accessible but secure - An accessible network allows for connections using dedicated, dialup, and switched services while maintaining network integrity.

The Cisco IOS offers a rich set of features that support network scalability. The remainder of this chapter outlines specific IOS features that work to promote these five key characteristics of a scalable network.