© 2006 Cisco Systems, Inc. All rights PublicITE I Chapter 6 1 Network Troubleshooting Accessing the…

© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicITE I Chapter 6 1

Network Troubleshooting

Accessing the WAN – Chapter 8

© 2006 Cisco Systems, Inc. All rights reserved. Cisco PublicITE 1 Chapter 6 2

Objectives Establish a network baseline

Describe troubleshooting methodologies and troubleshooting tools

Describe the common issues that occur during WAN implementation

Troubleshoot enterprise network implementation issues


Documenting Your Network

To efficiently diagnose and correct network problems, a network engineer needs to know how a network has been designed

What the expected performance for this network should be under normal operating conditions.

This information is called the network baseline and is captured in documentation such as configuration tables and topology diagrams.

Network configuration documentation provides a logical diagram of the network and detailed information about each component.

This information should be kept in a single location, either as hard copy or on the network on a protected website. Network documentation should include these components:

Network configuration table

End-system configuration table

Network topology diagram


Establish a Network Baseline


Conti…


Conti… Login :-login to undocumented device

Interface discovery:-Discover relevant information about the device

Document:-record device information in the network configuration table

Is it a component of the topology diagram:- is this device information important to add to the topology diagram.

Diagram:-transfer relevant device information from network configuration table to topology table.

Has the device been completely documented:-is there any more information to discover for this device.

Device discovery:-what neighboring devices are connected to this device

Were any device determined to be undocumented:- Are any of the neighbor device undocumented.

Network documentation complete:- if no undocumented device exist then documentation is complete.

E.g ping, telnet, show ip interface, show cdp neighbors etc.


Conti…


Planning for the First Baseline Step 1. Determine what types of data to collect e.g some good starting

measures are interface utilization and CPU utilization.

Step 2. Identify devices and ports of interest

Devices and ports of interest include:

Network device ports that connect to other network devices

Servers

Key users

Anything else considered critical to operatio


Measuring Network Performance Data

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.

This feature compares current performance levels with historical observations and can automatically identify performance problems and applications that do not provide expected levels of service.


General Approach to Troubleshooting Network engineers, administrators, and support personnel realize that

troubleshooting is a process that takes the greatest percentage their time.

Using efficient troubleshooting techniques shortens overall troubleshooting time when working in a production environment.

Two extreme approaches to troubleshooting almost always result in disappointment, delay, or failure.

At one extreme is the theorist, or rocket scientist, approach.

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. While this process is fairly reliable, few companies can afford to have their networks down for the hours or days that it can take for this exhaustive analysis.

At the other extreme is the impractical, or caveman, approach.

The caveman's first instinct is to start swapping cards, cables, hardware, and software until miraculously the network begins operating again.


Conti… Systematic method is the generally the best approach

to troubleshooting


Conti… Systematic Approach


Conti… The stages of the general troubleshooting process are:

Stage 1 Gather symptoms –

Stage 2 Isolate the problem –

Stage 3 Correct the problem –

These stages are not mutually exclusive. At any point in the process, it may be necessary to return to previous stages.


Troubleshooting Methods There are three main methods for troubleshooting networks:

Bottom up :- In bottom-up troubleshooting you start with the physical components of the network and move up through the layers of the OSI model until the cause of the problem is identified.

Top down :- In top-down troubleshooting your start with the end-user applications and move down through the layers of the OSI model until the cause of the problem has been identified.

Divide and conquer:- When you apply the divide-and-conquer approach toward troubleshooting a networking problem, you select a layer and test in both directions from the starting layer.

In divide-and-conquer troubleshooting you 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.


Gathering Symptoms Step 1. Analyze existing symptoms - Analyze symptoms gathered from

the trouble ticket, users, or end systems affected by the problem to form a definition of the problem.

Step 2. Determine ownership - If the problem is within your system. If the problem is outside the boundary of your control, for example, lost Internet connectivity outside of the autonomous system, you need to contact an administrator for the external system before gathering additional network symptoms.

Step 3. Narrow the scope - Determine if the problem is at the core, distribution, or access layer of the network.

Step 4. Gather symptoms from suspect devices - Using a layered troubleshooting approach, gather hardware and software symptoms from the suspect devices.

Step 5. Document symptoms - Sometimes the problem can be solved using the documented symptoms.


Conti… Stages for gathering symptoms for troubleshooting a

network problem


Troubleshooting Tools A wide variety of software and hardware tools are available to make

troubleshooting easier.

NMS Tools Network management system (NMS) tools include device-level monitoring,

configuration, and fault management tools.

Knowledge Bases On-line network device vendor knowledge bases have become

indispensable sources of information. When vendor-based knowledge bases are combined with Internet search engines like Google, a network administrator has access to a vast pool of experience-based information.

Baselining Tools Many tools for automating the network documentation and baselining

process are available. E.g SolarWinds LAN surveyor and CyberGauge software.


Conti… Protocol Analyzers A protocol analyzer decodes the various protocol layers in a recorded

frame and presents this information in a relatively easy to use format.


Hardware Troubleshooting 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.

The NAM is a embedded browser-based interface that generates reports on the traffic that consumes critical network resources.

In addition, the NAM can capture and decode packets and track response times to pinpoint an application problem to the network or the server.


Conti… Digital Multimeters Digital multimeters (DMMs) are test instruments that are used to directly

measure electrical values of voltage, current, and resistance.

Cable Testers Cable testers are specialized, handheld devices designed for testing the

various types of data communication cabling.

Cable Analyzers Cable analyzers are multifunctional handheld devices that are used to test

and certify copper and fiber cables for different services and standards.

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.


WAN Communication A communications provider or a common carrier normally owns the data

links that make up a WAN. The links are made available to subscribers for a fee and are used to

interconnect LANs or connect to remote networks.

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


Steps in WAN Design Step1:Locate LANs – Establish the source and destination endpoints that

will connect through the WAN.

Step2: Analyze traffic - Know what data traffic must be carried, its origin, and its destination.

Step 3. Plan the topology - The topology is influenced by geographic considerations but also by requirements such as availability.

Step 4. Estimate the required bandwidth - Traffic on the links may have varying requirements for latency and jitter

Step 5. Choose the WAN technology - Suitable link technologies must be selected.

Step 6. Evaluate costs - When all the requirements are established, installation and operational costs for the WAN can be determined and compared with the business need driving the WAN implementation.


Conit…


WAN Connection Technologies A typical private WAN uses a combination of technologies that are usually

chosen based on traffic type and volume.

ISDN(64 or 128 kb/s up to 2 Mb/s, PRI)

DSL(up to 3 Mb/s)

Frame Relay (up to 45 Mb/s)or

leased lines (up to 45 Mb/s (E3/T3) )are used to connect individual branches into an area.


Common WAN implementation issues


Summary Network Baseline

How a network is expected to perform under normal conditions

Network documentation should include:– Network configuration table– End-system configuration table– Network topology diagram

Planning for the 1st baseline– Determine what type of data to collect– Identify devices and ports of interest– Determine baseline duration


Summary

3 stages of the troubleshooting process–Gather symptoms–Isolate problem–Correct problem

3 main methods for troubleshooting a network–Bottom up–Top down–Divide & conquer


Summary

Software troubleshooting tools–Cisco view–Solar winds–HP Open view

Hardware troubleshooting tools–Network analysis mode–Digital multi-meters–Cable testers–Network analyzer


Summary

Common WAN implementation issues include–QoS–Reliability–Security–Latency–Confidentiality–Public or Private

Using a layered approach to troubleshooting aids in

isolating and solving the problem


Documents

© 2006 Cisco Systems, Inc. All rights PublicITE I Chapter 6 1 Network Troubleshooting Accessing the…