ENSA_Module_12_net_troubleshooting.pdf.pdf

17/10/2022 Module 12: Network Troubleshooting Enterprise Networking, Security, and Automation v7.0 (ENSA) 1 Module Objectives Module Title: Network Troubleshooting Module Objective: Troubleshoot enterprise networks. Topic Title...

17/10/2022 Module 12: Network Troubleshooting Enterprise Networking, Security, and Automation v7.0 (ENSA) 1 Module Objectives Module Title: Network Troubleshooting Module Objective: Troubleshoot enterprise networks. Topic Title Topic Objective Explain how network documentation is developed Network Documentation and used to troubleshoot network issues. Compare troubleshooting methods that use a Troubleshooting Process systematic, layered approach. Troubleshooting Tools Describe different networking troubleshooting tools. Determine the symptoms and causes of network Symptoms and Causes of Network Problems problems using a layered model. Troubleshooting IP Connectivity Troubleshoot a network using the layered model. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2 2 1  17/10/2022 12.1 Network Documentation © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3 3 Network Documentation Documentation Overview Accurate and complete network documentation is required to effectively monitor and troubleshoot networks. Common network documentation includes the following: Physical and logical network topology diagrams Network device documentation that records all pertinent device information Network performance baseline documentation All network documentation should be kept in a single location and backup documentation should be maintained and kept in a separate location. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 4 4 2  17/10/2022 Network Documentation Network Topology Diagrams There are two types of network topology diagrams: physical and logical. Physical Topology Logical Topology © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 5 5 Network Documentation Network Device Documentation Router Device Documentation Network device documentation should contain accurate, up-to- date records of the network hardware and Switch Device software. Documentation Documentation should include all pertinent information about the network devices. End-System Documentation © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 6 6 3  17/10/2022 Network Documentation Establish a Network Baseline A network baseline is used to establish normal network 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. The baseline data is as follows: Provides insight into whether the current network design can meet business requirements. Can reveal areas of congestion or areas in the network that are underutilized. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 7 7 Network Documentation 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, making analysis of the collected data difficult. Start out simply and fine-tune along the way. Some good starting variables are interface utilization and CPU utilization. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 8 8 4  17/10/2022 Network Documentation Step 2 - Identify Devices and Ports of Interest A logical network topology can be useful in identifying key devices and ports to monitor. As shown in the sample topology, the devices and ports of interest include: PC1 (the Admin terminal) Two servers (i.e., Srv1 and Svr2) Router interfaces Key ports on switches © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 9 9 Network Documentation Step 3 - Determine the Baseline Duration When capturing data for analysis, the period specified should be: At a minimum, seven days long. Last no more than six weeks, unless specific long-term trends need to be measured. Generally, a two-to-four-week baseline is adequate. Conduct an annual analysis of the entire network, or baseline different sections of the network on a rotating basis. Analysis must be conducted regularly to understand how the network is affected by growth and other changes. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 10 10 5  17/10/2022 Network Documentation Data Measurement The table lists some of the most common Cisco IOS commands used for data collection. Command Description Displays uptime, version information for device software and show version hardware show ip interface [brief] Displays all the configuration options that are set on an interface. show ipv6 interface [brief] show interfaces Displays detailed output for each interface. show ip route [static | eigrp | ospf | bgp] Displays the routing table content listing directly connected show ipv6 route [static | eigrp | ospf | bgp] networks and learned remote networks. Displays detailed information about directly connected Cisco show cdp neighbors detail devices. show arp Displays the contents of the ARP table (IPv4) and the neighbor show ipv6 neighbors table (IPv6). show running-config Displays current configuration. show vlan Displays the status of VLANs on a switch. show port Displays the status of ports on a switch. Used to collect a large amount of information using multiple show show tech-support commands for technical support reporting purposes. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 11 11 12.2 Troubleshooting Process © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 12 12 6  17/10/2022 Troubleshooting Process General Troubleshooting Procedures Troubleshooting can be time consuming because networks differ, problems differ, and troubleshooting experience varies. Using a structured troubleshooting method will shorten overall troubleshooting time. There are several troubleshooting processes that can be used to solve a problem. The figure displays the logic flowchart of a simplified three-stage troubleshooting process. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 13 13 Troubleshooting Process Seven-Step Troubleshooting Process The figure displays a more detailed seven- step troubleshooting process. Steps Description Define the Problem Verify that there is a problem and then properly define what the problem is. Gather Information Targets (i.e., hosts, devices) are identified, accessed, and information gathered. Analyze Identify possible causes using network documentation, network baselines, knowledge bases, and peers. Information Eliminate Possible Progressively eliminate possible causes to eventually identify the most probable cause. Causes Propose When the most probable cause has been identified, a solution must be formulated. Hypothesis Test Hypothesis Assess the urgency of the problem, create a rollback plan, implement the solution, and verify outcome. Solve the Problem When solved, inform all involved and document the cause and solution to help solve future problems. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 14 14 7  17/10/2022 Troubleshooting Process Seven-Step Troubleshooting Process The figure displays a more detailed seven- step troubleshooting process. Steps Description Define the Problem Verify that there is a problem and then properly define what the problem is. Gather Information Targets (i.e., hosts, devices) are identified, accessed, and information gathered. Analyze Information Identify possible causes using network documentation, network baselines, knowledge bases, and peers. Eliminate Possible Progressively eliminate possible causes to eventually identify the most probable cause. Causes Propose Hypothesis When the most probable cause has been identified, a solution must be formulated. Test Hypothesis Assess the urgency of the problem, create a rollback plan, implement the solution, and verify outcome. Solve the Problem When solved, inform all involved and document the cause and solution to help solve future problems. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 15 15 Troubleshooting Process Question End Users The table provides questioning guidelines and sample open ended end-user questions. Guidelines Example Open Ended End-User Questions What does not work? Ask pertinent questions. What exactly is the problem? What are you trying to accomplish? Who does this issue affect? Is it just you or others? Determine the scope of the problem. What device is this happening on? When exactly does the problem occur? Determine when the problem occurred / When was the problem first noticed? occurs. Were there any error message(s) displayed? Determine if the problem is constant or Can you reproduce the problem? intermittent. Can you send me a screenshot or video of the problem? Determine if anything has changed. What has changed since the last time it did work? Use questions to eliminate or discover What works? possible problems. What does not work? © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 16 16 8  17/10/2022 Troubleshooting Process Gather Information Common Cisco IOS commands used to gather network problem symptoms. Command Description ping {host |ip-address} Sends an echo request packet to an address, then waits for a reply. traceroute destination Identifies the path a packet takes through the networks. Connects to an IP address using the Telnet application (Note: Use telnet {host | ip-address} SSH whenever possible). ssh -l user-id ip-address Connects to an IP address using SSH. show ip interface brief Displays a summary status of all interfaces on a device. show ipv6 interface brief show ip route Displays the current IPv4 and IPv6 routing tables. show ipv6 route Displays the global and interface-specific status of any configured show protocols Layer 3 protocol. debug Displays a list of options for enabling or disabling debugging events. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 17 17 Troubleshooting Process Troubleshooting with Layered Models The OSI and TCP/IP models can be applied to isolate network problems when troubleshooting. The figure shows some common devices and the OSI layers that must be examined during the troubleshooting process for that device. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 18 18 9  17/10/2022 Troubleshooting Process Structured Troubleshooting Methods Different troubleshooting approaches that can be used include the following. Troubleshooting Description Approach Bottom-Up Good approach to use when the problem is suspected to be a physical one. Use this approach for simpler problems, or when you think the problem is with a Top-Down piece of software. Divide-and- Start at a middle layer (i.e, Layer 3) and tests in both directions from that layer. Conquer Used to discover the actual traffic path from source to destination to reduce the Follow-the-Path scope of troubleshooting. Substitution You physically swap a suspected problematic device with a known, working one. Attempts to resolve the problem by comparing a nonoperational element with the Comparison working one. Success of this method varies based on your troubleshooting experience and Educated guess © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 19 ability. 19 Troubleshooting Process Guidelines for Selecting a Troubleshooting Method To quickly resolve network problems, take the time to select the most effective network troubleshooting method. The figure illustrates which method could be used when a certain type of problem is discovered. Troubleshooting is a skill that is developed by doing it. Every network problem you identify and solve gets added to your skill set. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 20 20 10  17/10/2022 12.3 Troubleshooting Process © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 21 21 Troubleshooting Tools Software Troubleshooting Tools Common software troubleshooting tools include the following: Software Tool Description Network Network software include device-level monitoring, configuration, and fault- Management management tools. System Tools Tools can be used to investigate and correct network problems. Online network device vendor knowledge bases have become indispensable sources of information. Knowledge Bases When vendor-based knowledge bases are combined with internet search engines, a network administrator has access to a vast pool of experience- based information. Many tools for automating the network documentation and baselining process are available. Baselining Tools Baselining tools help with common documentation tasks such as network diagrams, update network software and hardware documentation, and cost- effectively measure baseline network bandwidth use. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 22 22 11  17/10/2022 Troubleshooting Tools Protocol Analyzers A protocol analyzer can capture and display the physical layer to the application layer information contained in a packet. Protocol analyzers, such as Wireshark, can help troubleshoot network performance problems. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 23 23 Troubleshooting Tools Hardware Troubleshooting Tools There are multiple types of hardware troubleshooting tools. Hardware Tools Description Digital Devices measure electrical values of voltage, current, and resistance. Multimeters Handheld devices are designed for testing the various types of data Cable Testers communication cabling. Cable Analyzers Multifunctional handheld devices used to test and certify copper and fiber cables. Portable Network Specialized device used for troubleshooting switched networks and VLANs. Analyzers Network Analysis Module is a browser-based interface that displays device Cisco Prime NAM performance analysis in a switched and routed environment. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 24 24 12  17/10/2022 Troubleshooting Tools Syslog Server as a Troubleshooting Tool Syslog is used by syslog clients to send text-based log messages to a syslog server. Log messages can be sent to the console, VTY lines, Level Keyword memory buffer, or syslog server. Cisco IOS log messages fall into one of eight levels. 0 Emergencies The lower the level number, the higher the severity level. 1 Alerts By default, the console displays level 7 (debugging) 2 Critical messages. 3 Errors In the command output, level 0 (emergencies) to 5 (notifications) are sent to the syslog server at 4 Warnings 209.165.200.225. 5 Notifications 6 Informational 7 Debugging © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 25 25 12.4 Symptoms and Causes of Network Problems © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 26 26 13  17/10/2022 Symptoms and Causes of Network Problems Physical Layer Troubleshooting The table lists common symptoms of physical layer network problems. Symptom Description Performance Requires previous baselines for comparison. lower than The most common reasons include overloaded or underpowered servers, unsuitable switch or baseline router configurations, traffic congestion on a low-capacity link, and chronic frame loss. Loss of connectivity could be due to a failed or disconnected cable. Loss of Can be verified using a simple ping test. connectivity Intermittent connectivity loss can indicate a loose or oxidized connection. Network If a route fails, routing protocols could redirect traffic to sub-optimal routes. bottlenecks or This can result in congestion or bottlenecks in parts of the network. congestion High CPU High CPU utilization rates indicates that a device is operating at or exceeding its design limits. utilization rates If not addressed quickly, CPU overloading can cause a device to shut down or fail. Console error Error messages reported on the device console could indicate a physical layer problem. messages Console messages should be logged to a central syslog server. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 27 27 Symptoms and Causes of Network Problems Physical Layer Troubleshooting (Cont.) The table lists issues that commonly cause network problems at the physical layer. Problem Cause Description Power-related Check the operation of the fans and ensure that the chassis intake and exhaust vents are clear. Faulty or corrupt NIC driver files, bad cabling, or grounding problems can cause network Hardware faults transmission errors such as late collisions, short frames, and jabber. Look for damaged cables, improper cable, and poorly crimped connectors. Cabling faults Suspect cables should be tested or exchanged with a known functioning cable. Attenuation can be caused if a cable length exceeds the design limit for the media, or when there Attenuation is a poor connection resulting from a loose cable, or dirty or oxidized contacts. Local electromagnetic interference (EMI) can be generated by many sources, such as crosstalk, Noise nearby electric cables, large electric motors, FM radio stations, police radio, and more. Interface Causes can include incorrect clock rate, incorrect clock source, and interface not being turned on. configuration errors This causes a loss of connectivity with attached network segments. Exceeding design A component could operate sub-optimally if it is being utilized beyond specifications. limits Symptoms include processes with high CPU utilization percentages, input queue drops, slow CPU overload performance, SNMP timeouts, no remote access, no DHCP services, Telnet, and pings are slow or fail to respond. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 28 28 14  17/10/2022 Symptoms and Causes of Network Problems Data Link Layer Troubleshooting The table lists common symptoms of data link layer network problems. Symptom Description No functionality or connectivity Some Layer 2 problems can stop the exchange of frames across a link, while others only at the network layer or above cause network performance to degrade. Frames can take a suboptimal path to their destination but still arrive causing the Network is operating below network to experience unexpected high-bandwidth usage on links. baseline performance levels An extended or continuous ping can help reveal if frames are being dropped. Operating systems use broadcasts and multicasts extensively. Excessive broadcasts Generally, excessive broadcasts are the result of a poorly programmed or configured applications, a large Layer 2 broadcast domains, or an underlying network problems. Routers send messages when it detects a problem with interpreting incoming frames (encapsulation or framing problems) or when keepalives are expected but do not arrive. Console messages The most common console message that indicates a Layer 2 problem is a line protocol down message © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 29 29 Symptoms and Causes of Network Problems Data Link Layer Troubleshooting The table lists issues that commonly cause network problems at the data link layer. Problem Cause Description Encapsulation errors Occurs when bits placed in a field by the sender are not what the receiver expects to see. Address mapping Occurs when Layer 2 and Layer addressing is not available. errors Framing errors Framing errors can be caused by a noisy serial line, an improperly designed cable, faulty NIC, duplex mismatch, or an incorrectly configured channel service unit (CSU) line clock. STP failures or loops Most STP problems are related to forwarding loops that occur when no ports in a redundant topology are blocked and traffic is forwarded in circles indefinitely, excessive flooding because of a high rate of STP topology changes. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 30 30 15  17/10/2022 Symptoms and Causes of Network Problems Network Layer Troubleshooting The table lists common symptoms of network layer network problems. Symptom Description Occurs when the network is nearly or completely non-functional, affecting all users and applications on the network. Network failure These failures are usually noticed quickly by users and network administrators and are obviously critical to the productivity of a company. These involve a subset of users, applications, destinations, or a type of traffic. Optimization issues can be difficult to detect and even harder to isolate and Suboptimal diagnose. performance This is because they usually involve multiple layers, or even a single host computer. Determining that the problem is a network layer problem can take time. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 31 31 Symptoms and Causes of Network Problems Network Layer Troubleshooting (Cont.) The table lists common symptoms of network layer network problems. Problem Cause Description Often a change in the topology may unknowingly have effects on other areas of the network. General network issues Determine whether anything in the network has recently changed, and if there is anyone currently working on the network infrastructure. Check for any equipment and connectivity problems, including power Connectivity issues problems, environmental problems, and Layer 1 problems, such as cabling problems, bad ports, and ISP problems. Check the routing table for anything unexpected, such as missing routes or Routing table unexpected routes. Check to see if there are any problems with the routers forming neighbor Neighbor issues adjacencies. Check the table for anything unexpected, such as missing entries or Topology database unexpected entries. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 32 32 16  17/10/2022 Symptoms and Causes of Network Problems Transport Layer Troubleshooting - ACLs The table lists areas where ACL misconfigurations commonly occur. Misconfigurations Description Selection of traffic flow An ACL must be applied to the correct interface in the correct traffic direction. Order of access control entries The entries in an ACL should be from specific to general. Implicit deny any The implicit ACE can be the cause of an ACL misconfiguration. Complex IPv4 wildcard masks are more efficient, but are more subject to Addresses and IPv4 wildcard masks configuration errors. Selection of transport layer protocol It is important that only the correct transport layer protocol be specified in an ACE. Source and destination ports Ensuring that the correct inbound and outbound ports are specified in an ACE Use of the established keyword The established keyword applied incorrectly, can provide unexpected results. Uncommon protocols Misconfigured ACLs often cause problems for protocols other than TCP and UDP. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 33 33 Symptoms and Causes of Network Problems Transport Layer Troubleshooting - NAT for IPv4 The table lists common interoperability areas with NAT. Symptom Description The DHCP-Request packet has a source IPv4 address of 0.0.0.0. However, NAT requires both a valid destination and source IPv4 address, BOOTP and DHCP therefore, BOOTP and DHCP can have difficulty operating over a router running either static or dynamic NAT. Configuring the IPv4 helper feature can help solve this problem. A DNS server outside the NAT router does not have an accurate representation DNS of the network inside the router. Configuring the IPv4 helper feature can help solve this problem. An SNMP management station on one side of a NAT router may not be able to SNMP contact SNMP agents on the other side of the NAT router. Configuring the IPv4 helper feature can help solve this problem. Encryption and tunneling protocols often require that traffic be sourced from a Tunneling and encryption protocols specific UDP or TCP port, or use a protocol at the transport layer that cannot be processed by NAT. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 34 34 17  17/10/2022 Symptoms and Causes of Network Problems Application Layer Troubleshooting The table provides a short description of these application layer protocols. Applications Description SSH/Telnet Enables users to establish terminal session connections with remote hosts. Supports the exchanging of text, graphic images, sound, video, and other multimedia HTTP files on the web. FTP Performs interactive file transfers between hosts. TFTP Performs basic interactive file transfers typically between hosts and networking devices. SMTP Supports basic message delivery services. POP Connects to mail servers and downloads email. SNMP Collects management information from network devices. DNS Maps IP addresses to the names assigned to network devices. Network File System (NFS) enables computers to mount and use drives on remote NFS hosts. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 35 35 12.5 Troubleshooting IP Connectivity © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 36 36 18  17/10/2022 Troubleshooting IP Connectivity Components of Troubleshooting End-to-End Connectivity Bottom-up approach steps when there is no end-to-end connectivity are as follows: 1. Check physical connectivity at the point where network communication stops. 2. Check for duplex mismatches. 3. Check data link and network layer addressing on the local network. 4. Verify that the default gateway is correct. 5. Ensure that devices are determining the correct path from the source to the destination. 6. Verify the transport layer is functioning properly. 7. Verify that there are no ACLs blocking traffic. 8. Ensure that DNS settings are correct. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 37 37 Troubleshooting IP Connectivity End-to-End Connectivity Problem Initiates Troubleshooting Usually what initiates a troubleshooting effort is the discovery that there is a problem with end-to-end connectivity. Two of the most common utilities used to verify a problem with end-to-end connectivity are ping and traceroute. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 38 38 19  17/10/2022 Troubleshooting IP Connectivity Step 1 - Verify the Physical Layer The show interfaces command is useful when troubleshooting performance- related issues and hardware is suspected to be at fault. Of interest in the output are the: Interface status Input queue drops Output queue drops Input errors Output errors © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 39 39 Troubleshooting IP Connectivity Step 2 - Check for Duplex Mismatches The IEEE 802.3ab Gigabit Ethernet standard mandates the use of autonegotiation for speed and duplex and practically all Fast Ethernet NICs also use autonegotiation by default. Problems can occur when there is a duplex mismatch. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 40 40 20  17/10/2022 Troubleshooting IP Connectivity Step 3 - Verify Addressing on the Local Network The arp Windows command displays and modifies entries in the ARP cache that are used to store IPv4 addresses and their resolved Ethernet physical (MAC) addresses. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 41 41 Troubleshooting IP Connectivity Troubleshoot VLAN Assignment Example Another issue to consider when troubleshooting end-to-end connectivity is VLAN assignment. For example, the MAC address on Fa0/1 should The following configuration changes Fa0/1 to be in VLAN 10 instead of VLAN 1. VLAN 10 and verifies the change. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 42 42 21  17/10/2022 Troubleshooting IP Connectivity Step 4 - Verify Default Gateway Misconfigured or missing default gateways can cause connectivity problems. In the figure for example, the default gateways for: R1 is 192.168.1.2 (R2) PC1 is 10.1.10.1 (R1 G0/0/0) Useful commands to verify the default gateway on: R1: show ip route PC1: route print (or netstat –r) © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 43 43 Troubleshooting IP Connectivity Troubleshoot IPv6 Default Gateway Example An IPv6default gateway can be configured manually, using SLAAC, or by using DHCPv6. For example, a PC is unable to acquire its IPv6 R1 is enabled as an IPv6 router and now the configuration using SLAAC. The command output verifies that R1 is a member of ff02::2, output is missing the all IPv6-router multicast the All-IPv6-Routers multicast group. group (FF02::2). © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 44 44 22  17/10/2022 Troubleshooting IP Connectivity Step 5 - Verify Correct Path When troubleshooting, it is often necessary to verify the path to the destination network. The figure describes the process for both the IPv4 and IPv6 routing tables. The process of forwarding IPv4 and IPv6 packets is based on the longest bit match or longest prefix match. The routing table process will attempt to forward the packet using an entry in the routing table with the greatest number of leftmost matching bits. The number of matching bits is indicated by the prefix length of the route. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 45 45 Troubleshooting IP Connectivity Step 6 - Verify the Transport Layer Two of the most common issues that affect transport layer connectivity include ACL configurations and NAT configurations. A common tool for testing transport layer functionality is the Telnet utility. For example, the administrator attempts to Telnet to R2 using port 80. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 46 46 23  17/10/2022 Troubleshooting IP Connectivity Step 7 - Verify ACLs On routers, there may be ACLs that prohibit protocols from passing through the interface in the inbound or outbound direction. In this example, ACL 100 has been incorrectly The ACL is removed from G0/0/0 and configured inbound on the G0/0/0 instead of configured inbound on S0/1/1. inbound on S0/1/1. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 47 47 Troubleshooting IP Connectivity Step 8 - Verify DNS The DNS protocol controls the DNS, a distributed database with which you can map hostnames to IP addresses. When you configure DNS on the device, you can substitute the hostname for the IP address with all IP commands, such as ping or telnet. command output. Use the ip host global configuration command to enter a name to be used instead of the IPv4 address of the switch or router, as shown in the command output. Use the nslookup Windows command to display the name- to-IP-address mapping information. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 48 48 24  17/10/2022 Troubleshooting IP Connectivity Packet Tracer - Troubleshoot Enterprise Networks In this Packet Tracer activity, you complete the following objectives: Part 1: Verify Switching Technologies Part 2: Verify DHCP Part 3: Verify Routing Part 4: Verify WAN Technologies Part 5: Verify Connectivity © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 49 49 12.6 Module Practice and Quiz © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 50 50 25  17/10/2022 Structured Design Packet Tracer – Network Troubleshooting In this Packet Tracer activity, you complete the following objectives: Test network connectivity. Compile host addressing information. Remotely access default gateway devices. Document default gateway device configurations. Discover devices on the network. Draw the network topology. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 51 51 Structured Design Packet Tracer – Troubleshoot Challenge – Use Documentation to Solve Issues In this Packet Tracer activity, you complete the following objectives: Use various techniques and tools to identify connectivity issues. Use documentation to guide troubleshooting efforts. Identify specific network problems. Implement solutions to network communication problems. Verify network operation. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 52 52 26  17/10/2022 Module Practice and Quiz What did I learn in this module? Common network documentation includes physical and logical network topologies, network device documentation, and network performance baseline documentation. The troubleshooting process should be guided by structured methods such as the seven-step troubleshooting process: (i.e., 1. Define the problem, 2. Gather information, 3. Analyze information, 4. Eliminate possible causes, 5. Propose hypothesis, 6. Test hypothesis, and 7. Solve the problem). Troubleshooting tools include NMS tools, knowledge bases, baselining tools, protocol analyzer, digital multimeters, cable testers, cable analyzers, portable network analyzers, Cisco Prime NAM, and syslog servers. Physical layer problems cause failures and suboptimal conditions. Data link layer problems are typically caused by encapsulation errors, address mapping errors, framing errors, and STP failures or loops. Network layer problems include IPv4, IPv6, routing protocols (such as EIGRP, OSPF, etc.). Transport layer problems can be misconfigured NAT or ACLs. Application layer problems can result in unreachable or unusable resources. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 53 53 Module Practice and Quiz What did I learn in this module? (Cont.) A bottom-up troubleshooting method can be used to solve connectivity problems. Start verifying the physical layer, check for duplex mismatches, verify addressing and default gateway, verify that the correct path is taken, and verify the transport layer. © 2012 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 54 54 27  17/10/2022 55 28