© 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE I Chapter 6 1 Network Troubleshooting Accessing the WAN – Chapter 8 Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 2 Objectives  In this chapter, you will learn to: – Establish and document a network baseline. – Describe the various troubleshooting methodologies and troubleshooting tools. – Describe the common issues that occur during WAN implementation. – Identify and troubleshoot common enterprise network implementation issues using a layered model approach. Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 3 Documenting Your Network  To efficiently diagnose and correct network problems, a network engineer needs to know network baseline . –This information is captured in documentation.  Network documentation include 3 components: 1. Network configuration table 2. End-system configuration table 3. Network topology diagram 1. Network Configuration Table –Contains up-to-date records of hardware and software •Type of device, model designation •IOS image name •Device network hostname •Location of the device (building, floor, room, rack, panel) •If it is a modular device, include all module types and in which module slot they are located •Data link layer addresses •Network layer addresses •Any additional important information about physical aspects of the device Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 4 Documenting Your Network 2. End-system Configuration Table –Contains baseline records used in end-system devices such as servers, and desktop workstations. •Device name (purpose) •Operating system and version •IP address •Subnet mask •Default gateway, DNS server, and WINS server addresses •Any high-bandwidth network applications that the end- system runs 3. Network Topology Diagram –Graphical representation of a network, which illustrates how each device in a network is connected and its logical architecture. –Routing protocols can also be shown. •Symbols for all devices and how they are connected •Interface types and numbers •IP addresses •Subnet masks Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 5 Network Documentation Process  When you document your network, you may have to gather information directly from routers and switches.  Commands that are useful to the network documentation process include: –The ping command is used to test connectivity with neighboring devices. Pinging to other PCs in the network also initiates the MAC address auto-discovery process. –The telnet command is used to log in remotely to a device for accessing configuration information. –The show ip interface brief is used to display the up or down status and IP address of all interfaces. –The show ip route command is used to display the routing table in a router to learn the directly connected neighbors, more remote devices (through learned routes), and the routing protocols. –The show cdp neighbor detail command is used to obtain detailed information about directly connected Cisco neighbor devices. Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 6 Why is Establishing a Baseline Important?  Establishing a network performance baseline requires collecting key performance data from the ports and devices that are essential to network operation. –How does the network perform during a normal or average day? • Measuring the initial performance allows a network administrator to determine the difference between abnormal behavior and proper network performance. –Where are the underutilized and over-utilized areas? • 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. –Where are the most errors occurring? • In addition, analysis after an initial baseline tends to reveal hidden problems. –What thresholds should be set for the devices that need to be monitored? –Can the network deliver the identified policies? • The baseline also provides insight into whether the current network design can deliver the required policies. Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 7 Steps for Establishing a Network Baseline 3 steps for planning the first baseline:  Step 1. Determine what types of data to collect –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. • Generally, some good 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 operations. –By narrowing the ports polled, the results are concise, and network management load is minimized. Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 8 Steps for Establishing a Network Baseline  Step 3. Determine the baseline duration –This period should be at least seven days to capture any daily or weekly trends. –A baseline needs to last no more than six weeks. –Generally, a two-to-four-week baseline is adequate. • The figure shows examples of several screenshots of CPU utilization trends captured over a daily, weekly, monthly, and yearly period. • The work week trends are too short to accurately reveal the recurring nature of the utilization surge that occurs every weekend when a database backup operation consumes network bandwidth. • The yearly trend shown in the example is too long a duration to provide meaningful baseline performance details. –Baseline analysis of the network should be conducted on a regular basis. • Analysis must be conducted regularly to understand how the network is affected by growth and other changes. Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 9 Measuring Network Performance Data  Sophisticated network management software is often used to baseline large networks. – For example, Fluke Network SuperAgent module enables administrators to automatically create reports using 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.  In simpler networks, the baseline tasks may require a combination of manual data collection and simple network protocol inspectors. – Hand collection using show commands on individual network devices is extremely time consuming and should be limited to mission- critical network devices. Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter 6 10 General Approach to Troubleshooting  Using efficient troubleshooting techniques shortens overall troubleshooting time.  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. • While this process is fairly reliable, few companies can afford to have their networks down for the hours or days. – At the other extreme is the impractical, or caveman, approach. • The caveman's first instinct is to start swapping cards, cables, and software until miraculously the network begins operating again. • This approach may achieve a change in symptoms faster, it is not reliable.  the better approach is somewhere in the middle using elements of both. – It is important to analyze the network as a whole rather than in a piecemeal fashion. – A systematic approach minimizes confusion and cuts down on time otherwise wasted with trial and error. [...]... identified –Stage 3 Correct the problem - Having isolated and identified the cause of the problem, the network administrator works to correct the problem by implementing, testing, and documenting a solution If the network administrator determines that the corrective action has created another problem, the attempted solution is documented, the changes are removed, and the network administrator returns to gathering... is a the customer internal problem •This is why a network baseline is so important –Link from the edge of the user network to the edge of the ISP •This problem is ISP's responsibility –Backbone of the ISP the ISP can determine which link is causing the problem –Server being accessed •In some cases the slowness, being attributed to the network, may be caused by server congestion This problem is the. .. 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 WAN data transfer speed (bandwidth) is considerably slower than the common LAN bandwidth The charges for link provision are the major cost element, therefore the WAN implementation must aim to provide maximum bandwidth at acceptable cost ITE 1 Chapter 6 © 2006... system 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 –Use knowledge and experience to determine if the problem is a hardware or software problem Step 5 Document symptoms –Sometimes the problem can be solved using the documented symptoms If not, begin the isolating phase of the general troubleshooting... Nguyen Networking Academy WAN Traffic Considerations The table in the figure shows the wide variety of traffic types and their varying requirements of bandwidth, latency, and jitter that WAN links are required to carry –To determine traffic flow conditions and timing of a WAN link, you need to analyze the traffic characteristics specific to each LAN that is connected to the WAN ITE 1 Chapter 6 © 2006 Cisco... links –A three-layer hierarchy is often useful when the network traffic mirrors the enterprise branch structure and is divided into regions, areas, and branches •Group the LANs in each area and interconnected them to form a region, – The area could be based on the number of locations to be connected with an upper limit of between 30 and 50 – The area would have a star topology, with the hubs of the stars... presentation, and application The transport layers of TCP/IP is responsible for exchanging segments between devices The Internet layer is responsible for placing messages in a fixed format that allows devices to handle them The network access layer communicates directly with the network media and provides an interface between the architecture of the network and the Internet layer ITE 1 Chapter 6 © 2006 Cisco... Troubleshooting Procedures The stages of the general troubleshooting process are: –Stage 1 Gather symptoms - Troubleshooting begins with the process of gathering and documenting symptoms from the network, end systems, and users •Symptoms may appear in many different forms, including alerts from the network management system, console messages, and user complaints –Stage 2 Isolate the problem - The problem is not... Public 25 Cisco Thai Nguyen Networking Academy WAN Topology Considerations Designing a WAN topology consists of the following: – Selecting an interconnection pattern or layout for the links between the various locations – Selecting the technologies for those links to meet the enterprise requirements at an acceptable cost • More links increase the cost of the network services, but having multiple paths... 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 •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 ITE 1 Chapter 6 © 2006 Cisco . Public ITE I Chapter 6 1 Network Troubleshooting Accessing the WAN – Chapter 8 Cisco Thai Nguyen Networking Academy © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public ITE 1 Chapter. to other PCs in the network also initiates the MAC address auto-discovery process. The telnet command is used to log in remotely to a device for accessing configuration information. The. 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