The Roles of Routers and Switches

Over the last fifteen years, the field of networking has evolved at a rapid pace. Much of this evolution has been driven by the need for sharing network resources and data along with the newer demands of video and voice. In addition, a mobile workforce has placed its own demands on networks. Network professionals face numerous challenges as networks evolve and network traffic increases.

In fact, it's not uncommon to address traffic congestion by breaking a large network into smaller networks, a process known as network segmentation. Using routers, bridges, and switches, network professionals address traffic congestion which can be caused by low bandwidth, broadcast storms, multicasting, too many hosts, excessive IPX or ARP traffic, and other factors.

Routers connect networks together, routing data between the connected networks. Broadcast domains are broken once a router has been put into place. When a network broadcast goes out, all network devices must process the information whether they need it or not. If a broadcast domain is too big, network devices must process more broadcasts resulting in slow network responses. By breaking up these domains with a router, the router can discard the broadcast and not forward it to its connected networks and devices. Routers also break up collision domains, too.

Using routers is advantageous because they do not forward broadcasts automatically. In addition, they can examine network layer information such as an IP address to filter the network. Routers serve several functions including: path selection, internetwork communication, packet switching, and packet filtering,

Switches serve a different purpose, adding functionality, improving LAN performance, and increasing bandwidth. While routers (layer 3 switches) "route" packets, switches (layer 2 switches) "switch" frames between ports in the switched network. Switches form a single broadcast domain but create separate collision domains while routers break up both broadcast and collision domains.

Routers provide "packet switching" using logical addressing and "packet filtering" using access-lists. When two or more networks are connected with a router using IP addresses, the resulting network is referred to as an "internetwork." A routing table of the internetwork allows routers to select paths and forward packets.

While there are endless ways to configure a network, the best one is one that meets business requirements. One LAN design may be perfect for one business but a complete failure for another due to varying business requirements. By thoroughly understanding Cisco internetworking topics, you'll be better able to configure a LAN that meets all business requirements using routers and switches.

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