When networks are originally designed and installed, user requirements are
gathered, analyzed, and translated into a network topology. The user
requirements may be further extended into network performance goals such as
bandwidth utilization, network latency and delay, and collision and error
thresholds. To validate and document that the goals were achieved, specialized
network monitoring and data collection is required. The process of network
monitoring and data collection is called baselining.
Baselining allows discovery of the true performance and operation of the
network in terms of the policies that have been defined. Performance trends and
faults may be identified by comparing future performance metrics to the
baseline metrics.
Establishing a baseline for a network provides answers
to the following questions:
- How does the network perform during a normal or average day?
- Where are the under-utilized and over-utilized areas?
- Where are the most errors occurring?
- What thresholds should be set for the devices that need to be monitored?
- Can the network deliver the identified policies?
The purpose of conducting a network baseline is to measure the initial
performance and availability of critical network devices and links in order to
compare them to future performance. The baseline allows a network administrator
to determine the difference between abnormal behavior and proper network
performance. It also provides insight into whether the current network design
can deliver the required policies.
Sophisticated network management
software is often used to baseline large and complex networks. In simpler
networks, the baseline tasks may require a combination of manual data
collection and simple network protocol inspectors. The Fluke Protocol Expert is
an example of one network protocol inspector. Shareware protocol inspectors can
be downloaded from the Internet at http://www.statscout.com or other
shareware sites. Selected examples of tools that may be used for baselining are
discussed in Module 2, "Troubleshooting Methodologies and Tools"
.
The collected data will reveal the true nature of congestion or potential
congestion in a network. It may also reveal areas in the network that are
underutilized. Analysis after an initial baseline tends to reveal hidden
problems and quite often can lead to network redesign efforts based on quality
and capacity observations.
Without a baseline, no standard exists to
measure the optimum nature of network traffic and congestion levels.
Establishing an initial baseline or conducting a performance monitoring
analysis may require many hours or days to accurately reflect network
performance. Network management software or protocol inspectors and sniffers
may run continuously over the course of the data collection process. Hand
collection by way of show commands on individual network
devices is extremely time consuming and should be limited to mission critical
network devices.
The following sections describe the general methodology
for defining, collecting, and reporting a network performance baseline. This
entails the collection of key performance data from the ports and devices
considered to be mission critical. The baseline is a vital preliminary step in
determining the "personality" of the network.
The following
are steps to building a baseline:
- Planning for the first baseline
- Identifying devices and ports of interest
- Determining the duration of the baseline