In most cases, "High utilization detected" is relatively straight forward to interpret if you keep in mind that Delivery monitoring reports end-to-end characteristics to each layer 3 device along a path. For example, if Delivery monitoring measured the test path as 67Mbps with 94% frequency of "High utilization detected" and no packet loss, experience will lead you to understand that these results are typical of a certain NIC card running down-level drivers. Upgrade the NIC drivers and typically the Total Capacity increases and Utilization will reflect the actual traffic on the wire.

A more normal scenario would be where Total Capacity is measured at 94Mbps, and no "High utilization detected" message appears. In both these cases, Total Capacity and Utilization reflect the Apparent Network that is available to the application. However, in the second case, Utilization is reflecting the effects of actual traffic on the wire rather than flaws in the NIC driver.

Note that it is important that good packet drivers are installed on the monitoring point, so that Delivery monitoring can achieve good test results. This will allow you to properly isolate which devices along the test path are flawed.

High router CPU utilization

Occasionally you may run across a situation where utilization is high at an intermediate hop, but not at the target hop.

Let’s look at the following diagram:


When testing "through" an intermediate router, very little delay is realized. However, when testing "to" the router, test packets leave the high-speed path and other delays may be experienced. Usually delays occur because of a busy router management CPU. Therefore, if you see high utilization on a hop in the middle of a network, you will inevitably find that the router CPU is overworked.

There can be several reasons for high CPU utilization on a router. Fragmentation of large router advertisement and Layer 2 multicast traffic patterns are two examples. Most often the problem arises by attempting to use a router as a firewall. Depending on how Access Control Lists (ACLs) are used, large volumes of traffic may get redirected away from high-speed ASICs towards the slower router management CPU. To reduce router CPU utilization, (thereby increasing overall router performance) consider reordering or reworking the ACL list on the affected router.