We've now covered the major pieces of technology that compose internetworks. Routers, switches, firewalls, and access servers are cabled together to form network topologies. Most configurations run over twisted-pair copper feeding into fiber-optic backbones that move data at speeds from 100 Mbps up to a mind-boggling 10 Gbps. While network devices vary in type and size, most look like PCs or servers in that they have memory, CPUs, and interface cards. They are, however, diskless, seldom have monitors, and use their interfaces to connect networks instead of peripherals.
Cisco's software infrastructure to make it all go is its various operating systems, like the Internetwork Operating System (IOS). IOS is a lean package of commands, protocol software, and the all-important config file. IOS software images differ greatly, depending on the type of device. The switch has a modest version of IOS, while the behemoth Cisco 12000 Series Gigabit Router is loaded with protocols and specialized management software packages. Regardless of device type or IOS functionality, network behavior is controlled by setting parameters in the config file.
As we saw in the previous chapter, perhaps the most sophisticated internetworking technology of all is the routing protocol. Routing protocols give internetworks a level of self-awareness and self-adaptation without which large-scale configurations wouldn't be practical. They do this by constructing a hierarchy of LANs and autonomous systems to find optimal paths to get across the office campus-or to the other side of the world.
It takes more than optimal routes to run an internetwork, though. The ability to selfoperate is only part of the network management equation. Routing protocols may be able to handle most minute-to-minute issues, but internetworks still require constant management effort from people. Without persistent review and intervention from administrators, an internetwork's ability to self-operate will be overwhelmed by a progressive deterioration in operating conditions. Internetworks must be constantly updated and even upgraded to accommodate problems, growth, and change. Network teams need tools for managing change and anticipating problems (and, hopefully, avoiding them).
If left alone, even a perfectly configured internetwork will degrade under the strain of added users, increased loads, shifting traffic, new hardware and software versions, and new technology. Network administrators must monitor, reconfigure, and troubleshoot without end. The recent boom in users-and the increase in the amount of traffic generated per user-has left network teams scrambling to keep up. Routing protocols and other automated features only make effective internetwork management feasible, they don't make it easy. Network management tools are needed also. The industry's response has been a stream of standards, technologies, and products focused on the configuration and operation of internetworks.