What should you do when you suspect network protocols are generating excessive traffic? Your answer may be the installation of a router.
In the first article of this series, I introduced Cisco Fusion, an integrated network architecture designed to solve networking problems in small- to medium-size businesses. Cisco divides such problems into three categories: media problems, protocol problems, and transport problems. Last week, we looked at media problems. In this installment, we’ll tackle the issue of protocol problems. You can catch up on our previous articles here:”Can Cisco Fusion solve your network problems? “”Is a switch the answer to your network problems?
Protocol problems occur when network protocols generate excessive network traffic, which can come in the form of multicast or broadcast packets.

The usual suspects
Network protocols such as AppleTalk and IPX generate considerable broadcast traffic. In a flat, switched network, this broadcast traffic is passed throughout the entire network. If there are too many devices on a segment, broadcast radiation can cause performance degradation.
Broadcast radiation refers to the way broadcast and multicast packets radiate from their source.
If broadcast and multicast traffic constitute more than 20 percent of LAN activity, it’s time to implement routing.

Take the router route
Unlike switches, which forward packets based on the MAC address (at the Data Link or second OSI layer), routers forward traffic based on OSI layer three (the Network layer). This layer uses the network address. Additionally, switches forward broadcasts to all connected segments. By default, routers do not forward broadcast traffic.

Routers, like switches, use tables to forward packets to their destination. However, routers only keep information on how to get to the remote networks, not to individual hosts. Routers offer increased functionality, manageability, and security. Using the Cisco IOS (Internetwork Operating System), a company’s routers can filter traffic, manage congestion, handle error and flow control, and provide multiple active paths to remote networks.

Of course, all of these added features do come at a cost. Because routers operate at the Network layer, they must examine more fields in a packet than a switch has to examine. Reading these additional fields adds overhead to the routing process that can result in a 30-40 percent loss of throughput. When routing time-sensitive applications like voice and video, the increased latency of the routing process can cause problems.

The challenge of moving large payloads through an internetwork is classified by Cisco’s small- to medium-size business framework as a transport problem. Join me next week for a detailed look at how to identify and resolve transport problems.

Warren Heaton CCDA, CCNA, MCSE+I is the Cisco Program Manager for A Technological Advantage in Louisville, KY.

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