Establish a Network Baseline (37.2.9)
The purpose of network monitoring is to watch network performance in comparison to a predetermined baseline. A baseline is used to establish normal network or system performance to determine the “personality” of a network under normal conditions.
Establishing a network performance baseline requires collecting performance data from the ports and devices that are essential to network operation.
A network baseline should answer the following questions:
- How does the network perform during a normal or average day?
- Where are the most errors occurring?
- What part of the network is most heavily used?
- What part of the network is least used?
- Which devices should be monitored and what alert thresholds should be set?
- Can the network meet the identified policies?
Measuring the initial performance and availability of critical network devices and links allows a network administrator to determine the difference between abnormal behavior and proper network performance as the network grows or traffic patterns change. The baseline also provides insight into whether the current network design can meet business requirements. Without a baseline, no standard exists to measure the optimum nature of network traffic and congestion levels.
Analysis after an initial baseline also tends to reveal hidden problems. The collected data shows the true nature of congestion or potential congestion in a network. It may also reveal areas in the network that are underutilized, and quite often can lead to network redesign efforts, based on quality and capacity observations.
The initial network performance baseline sets the stage for measuring the effects of network changes and subsequent troubleshooting efforts. Therefore, it is important to plan for it carefully.
Cisco Discovery Protocol (CDP) Overview (37.2.10)
The first thing you want to know about your network is what is in it. Where are these components? How are they connected? Basically, you need a map. This section explains how you can use Cisco Discovery Protocol (CDP) to create a map of your network.
CDP is a Cisco proprietary Layer 2 protocol that is used to gather information about Cisco devices that share the same data link. CDP is media and protocol independent and runs on all Cisco devices, such as routers, switches, and access servers.
The device sends periodic CDP advertisements to connected devices, as shown in Figure 37-19.
Figure 37-19 CDP Advertisements Sent Between a Router and a Switch
These advertisements share information about the type of device that is discovered, the name of the device, and the number and type of the interfaces.
Because most network devices are connected to other devices, CDP can assist in network design decisions, troubleshooting, and making changes to equipment. CDP can also be used as a network discovery tool to determine the information about the neighboring devices. This information gathered from CDP can help build a logical topology of a network when documentation is missing or lacking in detail.