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CCNA. Cisco Certified Network Associate. Documenting your network. To efficiently diagnose and correct network problems, a network engineer needs to know how a network has been designed and what the expected performance. Network documentation should include these components:
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CCNA Cisco Certified Network Associate
Documenting your network To efficiently diagnose and correct network problems, a network engineer needs to know how a network has been designed and what the expected performance. Network documentation should include these components: Network configuration table End-system configuration table Network topology diagram
Documenting your network Commands that are useful to the network documentation process include: Ping telnet Show ip interface brief Show ip route Show cdp neighbor detail
Establishing the network performance baseline This information helps to determine the "personality" of the network and provides answers to the following questions: How does the network perform during a normal or average day? Where are the underutilized 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?
Steps for establishing a network baseline Determine what types of data to collect some good starting measures are interface utilization and CPU utilization. Identify devices and ports of interest Network device ports that connect to other network devices Servers Key users Anything else considered critical to operations Determine the baseline duration t is important that the length of time and the baseline information being gathered are sufficient to establish a typical picture of the network. This period should be at least seven days to capture any daily or weekly trends. Weekly trends are just as important as daily or hourly trends. 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. You would get an inaccurate measure of network performance if you performed a baseline measurement on a holiday or during a month when most of the company is on vacation. Analysis must be conducted regularly to understand how the network is affected by growth and other changes.
Steps for establishing a network baseline Sophisticated network management software is often used to baseline large and complex networks. For example, the Fluke Network SuperAgent module enables administrators to automatically create and review reports using its Intelligent Baselines feature.
Methodologies and tools The rocket scientist analyzes and reanalyzes the situation until the exact cause at the root of the problem has been identified and corrected with surgical precision. The caveman's first instinct is to start swapping cards, cables, hardware, and software until miraculously the network begins operating again.
Using Layered Models if the symptoms suggest a physical connection problem, the network technician can focus on troubleshooting the circuit that operates at the Physical layer. If that circuit functions properly, the technician looks at areas in another layer that could be causing the problem.
Methods There are three main methods for troubleshooting networks: Bottom up Top down Divide and conquer
Methods - Bottom up good approach to use when the problem is suspected to be a physical one. Most networking problems reside at the lower levels, so implementing the bottom-up approach often results in effective results. it requires that you check every device and interface on the network until the possible cause of the problem is found. Remember that each conclusion and possibility must be documented so there can be a lot of paper work associated with this approach. A further challenge is to determine which devices to start examining first.
Methods – Top Down Use this approach for simpler problems or when you think the problem is with a piece of software. The disadvantage with the top-down approach is it requires checking every network application until the possible cause of the problem is found.
Methods – Divide and conquer start by collecting user experience of the problem, document the symptoms and then, using that information, make an informed guess as to which OSI layer to start your investigation. Once you verify that a layer is functioning properly, assume that the layers below it are functioning and work up the OSI layers. If an OSI layer is not functioning properly, work your way down the OSI layer model. For example, if users can't access the web server and you can ping the server, then you know that the problem is above Layer 3. If you can't ping the server, then you know the problem is likely at a lower OSI layer.
Software Tools A wide variety of software and hardware tools are available to make troubleshooting easier. These tools may be used to gather and analyze symptoms of network problems and often provide monitoring and reporting functions that can be used to establish the network baseline. NMS tools Knowledge bases Baselining tools Protocol analyzer
Software Tools – NMS Tools Network management system (NMS) tools include device-level monitoring, configuration, and fault management tools. Examples of commonly used network management tools are CiscoView, HP Openview, Solar Winds, and What's Up Gold.
Software Tools – Knowledge bases The figure shows the Cisco Tools & Resources page found at http://www.cisco.com. This is a free tool providing information on Cisco-related hardware and software. It contains troubleshooting procedures, implementation guides, and original white papers on most aspects of networking technology.
Software Tools – Baselining tools Many tools for automating the network documentation and baselining process are available. They can help you draw network diagrams, help you to keep network software and hardware documentation up-to-date and help you to cost-effectively measure baseline network bandwidth use.
Software Tools – Protocol analyzer A protocol analyzer decodes the various protocol layers in a recorded frame and presents this information in a relatively easy to use format. Most protocol analyzers can filter traffic that meets certain criteria so that, for example, all traffic to and from a particular device can be captured.
Hardware Tools Network Analysis Module Digital Multimeters Cable Testers Cable Analyzers Portable Network Analyzers
Hardware Tools - Network Analysis Module A network analysis module (NAM) can be installed in Cisco Catalyst 6500 series switches and Cisco 7600 series routers to provide a graphical representation of traffic from local and remote switches and routers.
Hardware Tools - Digital Multimeters Instruments that are used to directly measure electrical values of voltage, current, and resistance.
Hardware Tools - Cable Testers Cabling testers can be used to detect broken wires, crossed-over wiring, shorted connections, and improperly paired connections. These devices can be inexpensive continuity testers, moderately priced data cabling testers, or expensive time-domain reflectometers (TDRs). TDRs are used to pinpoint the distance to a break in a cable. These devices send signals along the cable and wait for them to be reflected.
Hardware Tools - Cable Analyzers Cable analyzers are multifunctional handheld devices that are used to test and certify copper and fiber cables for different services and standards. The more sophisticated tools include advanced troubleshooting diagnostics that measure distance to performance defect (NEXT, RL), identify corrective actions, and graphically display crosstalk and impedance behavior.
Hardware Tools - Portable Network Analyzers Portable devices that are used for troubleshooting switched networks and VLANs. By plugging the network analyzer in anywhere on the network, a network engineer can see the switch port to which the device is connected and the average and peak utilization. The analyzer can also be used to discover VLAN configuration, identify top network talkers, analyze network traffic, and view interface details.
Wan Comunications WAN data transfer speed (bandwidth) is considerably slower than the common LAN bandwidth. WANs carry a variety of traffic types, such as data, voice, and video. The design selected must provide adequate capacity and transit times to meet the requirements of the enterprise. topology of the connections between the various sites, the nature of those connections, and bandwidth capacity.
Interpreting network diagrams – Physical network diagram Device type Model and manufacturer Operating system version Cable type and identifier Cable specification Connector type Cabling endpoints
Interpreting network diagrams – Logical network diagram Device identifiers IP address and subnet Interface identifiers Connection type DLCI for virtual circuits Site-to-site VPNs Routing protocols Static routes Data-link protocols WAN technologies used
