Ethernet Performance

Ethernet networks tend to be susceptible to performance problems as they grow, based on the CSMA/CD method of media access that they use. While implementing Layer 2 switching goes a long way towards better Ethernet performance, there are still a number of issues to consider when an Ethernet network begins to experience performance problems. Examples of reasons for congestion on Ethernet networks include having too many hosts on a given segment, not enough bandwidth available, broadcast storms, along with excessive broadcast or multicast traffic.

A few key metrics are used by Cisco to help decide when an Ethernet network is not performing at an appropriate level. These include:

  • Network utilization. A network utilization of over 40% on shared Ethernet segments represents that the network is saturated.

  • Broadcasts/multicasts. No Ethernet segment should have more than 20% combined broadcast and multicast traffic.

  • CRC Errors. There should be less than 1 CRC error per MB of network traffic.

  • Collisions. Less than 0.1% of network packets should be involved in collisions

While this data may seem difficult to obtain, a variety of network management tools can provide these particular metrics, along with many others. Examples include CiscoWorks and Cisco Netsys Performance Service Manager.

Author: Dan DiNicolo

Dan DiNicolo is a freelance author, consultant, trainer, and the managing editor of He is the author of the CCNA Study Guide found on this site, as well as many books including the PC Magazine titles Windows XP Security Solutions and Windows Vista Security Solutions. Click here to contact Dan.