Logical sources of performance and availability issues

Insightful analysis by consultants Steve Taylor and Jim Metzler, plus links to the latest WAN news headlines

As was mentioned in the last WAN newsletter, an organization that has a large complex network needs visibility into the operational architecture and dynamic behavior of the network. However, given the distributed intelligence of IP combined with the fact that each router makes its own forwarding decision, there is no single repository of routing information in the network.

This lack of information is an issue because routing tables are automatically updated and the path that traffic takes to go from point A to point B may change on a regular basis. These changes may be precipitated by a manual process such as adding a router to the network, the misconfiguration of a router or by an automated process such as automatically routing around a failure.

The variability of how the network delivers application traffic across its multiple paths over time can undermine the fundamental assumptions that organizations count on to support many other aspects of application delivery, such as troubleshooting a problem. For example, routing instabilities can cause packet loss, latency, and jitter on otherwise properly configured networks. In addition, alternative paths might not be properly configured for QoS. As a result, applications perform poorly after a failure.

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As was mentioned in the last WAN newsletter, an organization that has a large complex network needs visibility into the operational architecture and dynamic behavior of the network. However, given the distributed intelligence of IP combined with the fact that each router makes its own forwarding decision, there is no single repository of routing information in the network.

This lack of information is an issue because routing tables are automatically updated and the path that traffic takes to go from point A to point B may change on a regular basis. These changes may be precipitated by a manual process such as adding a router to the network, the misconfiguration of a router or by an automated process such as automatically routing around a failure.

The variability of how the network delivers application traffic across its multiple paths over time can undermine the fundamental assumptions that organizations count on to support many other aspects of application delivery, such as troubleshooting a problem. For example, routing instabilities can cause packet loss, latency, and jitter on otherwise properly configured networks. In addition, alternative paths might not be properly configured for QoS. As a result, applications perform poorly after a failure.

The issue is that most IT organizations are well equipped to detect device specific failures such as device or interface failures, device out of memory condition or a failed link. However, the vast majority of IT organizations are not well equipped to detect logical factors such as sub-optimal routing or intermittent routing instability.

To identify the significance of this problem, we recently surveyed 188 IT professionals and asked them to indicate the percentage of time that an application is either unavailable or is exhibiting degraded performance is the cause logical? Is the cause device specific? Forty-two percent of the survey respondents indicated that at least half of the time, the cause was logical.

The next WAN newsletter will discuss route analytics, a technology that can help IT organizations gain visibility into the operational architecture and dynamic behavior of the network. Route analytics is one of the topics that will be discussed at Network World’s IT Roadmap conference, which will be held in Boston on March 6. If you live in the area, hopefully you will attend the conference.

Read more about lans & wans in Network World's LANs & WANs section.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Jim Metzler is vice president of Ashton, Metzler & Associates.