Content Overview To effectively
troubleshoot a network, a baseline must first be established.
The baseline information will be included in the network
documentation. This module discusses the basic requirements for
establishing a baseline and creating a coherent set of network
documentation. Some of the biggest challenges facing the IT
world are the expenses incurred as a result of network outages.
The negative impact of these expenses makes it a high priority
of network professionals to be able to diagnose and correct a
network problem as efficiently as possible. To assist in
accomplishing this, a baseline must be established to provide a
snapshot of the configuration of a network while it is
performing at an acceptable level. Using baseline information
as a standard reduces the time that a troubleshooter needs to
spend learning about the structure and configuration of the
network. It also helps troubleshooters know when they have
reached the goal of returning the network to its baseline
level. Without a baseline, troubleshooters have to make guesses
and estimates about whether they have reached their goal.
Troubleshooting in this manner is haphazard and inefficient.
Content 1.1 Network Baselining
1.1.1 Network baselining overview When networks
are first designed and installed, user requirements are
gathered, analyzed, and translated into a network topology that
satisfies the user requirements. The user requirements may be
further extended into network performance goals such as
bandwidth utilization, network latency and delay, and collision
and error thresholds. In order to validate and document that
the goals were achieved, specialized network monitoring and
data collection is required. The process of network monitoring
and collecting data is called baselining. The interpretation of
the collected data is called baseline, or performance,
analysis. 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. After identifying data of interest for a policy,
baselining allows a snapshot of the current state of variables
throughout the network. Establishing a baseline for a network
provides answers to the following questions: - How does
the network perform day to 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. The
task of baselining can best be accomplished in large, complex
networks, using sophisticated network management software with
integrated remote monitoring network devices. In simpler
networks, these data collection tasks may require a combination
of hand collection of data, augmented with simple network
protocol instectors like Fluke Protocol Inspector or other
shareware utilities that can be downloaded from the Internet at
sites such as http://www.statscout.com. 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. Another reason for conducting a baseline is that
no two networks operate or behave the same way. 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, by
collecting current data and comparing it to the baseline,
require sufficient time 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. It also simplifies
the setting of effective thresholds. 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
Content 1.1 Network Baselining 1.1.2
Planning for the first baseline When conducting the
initial baseline, start by selecting a few variables that
represent the defined policies. If too many data points are
selected, the amount of data can be overwhelming, making
analysis of the collected data difficult. Hence, start out
simply and fine tune along the way. Generally, some good
starting measures are interface utilization and CPU
utilization. Collect data for a day or two before starting the
actual baseline study to determine whether the right data is
being gathered from the right devices. After recording a couple
of days’ worth of data, graph the collected data in different
ways in order to better show where the network needs
improvement. Slicing through the data in different ways can
reveal interesting and sometimes surprising observations. Pick
the top few reports that are relevant and study them to
determine whether there is more information needed, in order to
understand a particular pattern or trend. Then, fine tune the
data to be collected and begin the actual baseline study.
Baseline analysis of the network should be conducted on a
regular basis. Perform an annual analysis of the entire network
or baseline different sections of the network on a rotating
basis. Analysis must be conducted regularly in order to
understand how the network is affected by growth and other
changes. Gathering the information in a consistent manner and
analyzing the data will allow informed design decisions as well
as expedite fault isolation.
Content 1.1
Network Baselining 1.1.3 Identifying devices
and ports of interest As part of planning a baseline, the
devices and ports of interest must be identified. Ports of
interest include those network device ports that connect to
other network devices, servers, key users, and anything else
considered critical to the operation. By narrowing the ports
polled, the reports will be more clear and network and device
management load will be minimized. Remember that an interface
on a router or switch can be a virtual interface, such as a
switch virtual interface (SVI). After the ports have been
identified, it must be ensured that processes are in place to
either keep that connection from being changed or to generate a
report informing the network administrator that a change has
occurred. Without this assurance, reports will become
inaccurate. A report may indicate that a backbone port on a
particular device is performing fine, when in fact the device
connected to that port is not a router, but a PC, due to an
undocumented change. One method to track the ports of interest
is to use the port description fields on devices to indicate
what is connected. If backbone Router A is connected to switch