port 1/1 on the main campus, the port description
on switch port 1/1 should be configured for the device (Router
A) on the other end. The port description can then be used for
adding clarity to the reports created from the baseline and
performance monitoring.
Content 1.1 Network
Baselining 1.1.4 Determining the duration of
the baseline IIt is important that the length of time and
the baseline information being gathered is sufficient to
establish a typical picture of the network. This period should
be at least seven days, in order to capture any daily or weekly
trends. Weekly trends are just as important as daily or hourly
trends. As an example, the engineers in Building 7 run a
massive backup and software refresh, on Sundays at 2 A.M., on
all 200 of their workstations. Because the backup server
happens to be in Building 9, the push and backup saturate the
corporate backbone. If the baseline was only performed from
Monday through Friday, the saturation would be missed. A
baseline needs to last no more than six weeks unless specific
long-term trends need to be measured. Generally, a
two-to-four-week baseline is adequate. Examples of baselines
for CPU utilization over various intervals of time can be
provided by the Multi Router Traffic Grapher (MRTG). This tool
can be found at http://mrtg.hdl.com/mrtg.html. It is
recommended that baseline measurement is not performed during
times of unique traffic patterns. As an example, it would not
be beneficial to perform the baseline over a holiday or during
December if most of the company is on vacation. However long
the initial baseline is chosen to last, plan to try different
durations on subsequent baselines. This will allow discovery of
the optimal analysis collection interval for the network.
Content 1.1 Network Baselining 1.1.5
Using the baseline data This is where all the attention
to detail when collecting baseline information pays off.
Policies have been defined including variables that measure the
policies. Also, data has been collected from critical devices
and connections for a period of time. By performing baseline
tests on the network, it is possible to gain a better
understanding of capacity and quality of service a network
delivers. Now it is time to analyze the snapshot. The data can
be used in the following ways to learn more about the network:
- Identifying undesired network behavior
- Identifying thresholds for fault and performance monitoring
- Predicting long-term performance and capacity trends
- Verifying policies
Content
1.1 Network Baselining 1.1.6
Identifying undesired network behavior An immediate benefit
of baselining the network is the objective identification of
undesired network behavior. By generating reports that identify
the most utilized lines, areas of the network that are either
experiencing problems or are prime candidates for failure, can
be readily identified. At the same time, under-utilized areas
of the network can be identified. Where redundancy is involved,
it may be discovered that traffic is routing almost entirely
over only one of the redundant connections. This may be
undesirable because the bandwidth could be almost doubled in a
properly configured network with load sharing. The
identification of undesired network behavior may lead to a
network redesign or a change in network policy. It may also be
discovered that a device is configured incorrectly.
Content 1.1 Network Baselining 1.1.7
Identifying thresholds Efficient troubleshooting
requires the setting of thresholds that reflect different
levels of warning. Arriving at the appropriate thresholds for
each of the network policies requires a baseline analysis.
Initially, most network administrators consult the network
device documentation or vendor technical support for a set of
recommended or default thresholds. Generally, the answer
received is It depends the thresholds vary according to
individual networks. Unfortunately, the nature of distributed
networking forces the process of identifying or predicting a
fault to be somewhat of an art form. Vendors who develop
performance and fault tools may provide a set of defaults.
Generally these default settings must be fine tuned to meet the
needs of individual networks. The baseline analysis provides
the data to study performance and fault patterns over a period
of time. From this data, the appropriate thresholds can be
determined, as it applies to network policies.
Content
1.1 Network Baselining 1.1.8
Predicting long-term performance and capacity trends As
part of the planning cycle for the network, it is necessary to
study network growth over a period of time. This study will
provide understanding of how the network may continue to grow
and provide data for obtaining funds for network expansion. As
stated earlier, baseline studies should be scheduled on a
regular basis. By comparing the data from each baseline,
long-term growth trends can be isolated. These types of reports
tend to be reported in terms of total bandwidth or total
capacity for each link, for each device, and for the network as
a whole. Network growth tends to occur in large bursts.
Monitoring the hardware components is just one aspect of
maintaining the performance of the network. The network
administrator must also coordinate the use and upgrade of
software applications, adjusting the network configuration,
accordingly.
Content 1.1 Network Baselining
1.1.9 Verifying policies Determining
whether a policy can be achieved in the network is a good use
of a network baseline. By reporting the data in terms of the
defined policies, it can be determined whether the network is
adhering to or violating a policy, and to what degree adherence
or violations are occurring. Figure displays a sample network
policy that often specifies the consequences of policy
violations. If the data reflects a policy violation, the issue
must be resolved. - How serious is the violation?
- How often does it occur?
- How long does it last?
- Is the source of the violation an incorrect
configuration?
Either the policy must be redefined,
based on what the network currently delivers or a network
redesign might be required. If the study reveals the need for a
network redesign, data from the baseline analysis can be used
objectively to justify the need for new equipment or service
purchases.
Content 1.2 Network Configuration
Documentation 1.2.1 Network configuration
documentation overview When troubleshooting a network, a
troubleshooter uses a baseline to efficiently diagnose and
correct network problems. The baseline information for a
network is captured in documentation such as network
configuration tables and topology diagrams. This section
discusses the creation of relevant and accurate network
documentation as a troubleshooting tool for returning an
underperforming, or failing, network back to an acceptable
condition. The information contained in this section assumes a
worst-case scenario where the network administrator is almost
completely unfamiliar with a network and needs to create
documentation from scratch. Useful network documentation will
facilitate more effective troubleshooting, thereby saving time
and effort. When the configuration of the network is failing or
underperforming, a network configuration table will provide a
saved configuration that should perform at an acceptable level.
Network documentation will also eliminate the time-consuming
and error-prone process of creating a network configuration
from scratch. Network configuration documentation should
include elements that provide a logical diagram of the network
and detailed information about each component. The
troubleshooter should find this information in a single
location, either hard copy or on the network at a protected
website. At a minimum, network documentation should include the
following details: - Network configuration tables