ITIS 152/CISN 342 CCNA Enterprise Networking, Security, and Automation (ENSA) Module 12: Network Troubleshooting

Network Topology Diagram

A documented map of network devices that includes the patterns or design used to connect the devices, either physically or logically.

Power-Related Problem

Check the operation of the fans and ensure that the chassis intake and exhaust vents are clear.

Interface Configuration Errors

Causes can include incorrect clock rate, incorrect clock source, and interface not being turned on. This causes a loss of connectivity with attached network segments.

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.

Source And Destination Ports Misconfiguration

Ensuring that the correct inbound and outbound ports are specified in an ACE

Exceeding Design Limits Problem

A component could operate sub-optimally if it is being utilized beyond specifications.

Seven-Step Troubleshooting Process

A troubleshooting process that breaks the troubleshooting process into more detailed steps than the three-step process.

Selection Of Traffic Flow Misconfiguration

An ACL must be applied to the correct interface in the correct traffic direction.

Test Hypothesis (Step 6 of 7)

Assess the urgency of the problem, create a rollback plan, implement the solution, and verify outcome.

Comparison Troubleshooting Approach

Attempts to resolve the problem by comparing a nonoperational element with the working one.

Attenuation Problem

Attenuation can be caused if a cable length exceeds the design limit for the media, or when there is a poor connection resulting from a loose cable, or dirty or oxidized contacts.

Cisco Prime Network Analysis Module (NAM)

Browser-based interface that displays device performance analysis in a switched and routed environment.

Addresses and IPv4 Wildcard Masks Misconfiguration

Complex IPv4 wildcard masks are more efficient, but are more subject to configuration errors.

Digital Multimeters

Devices measure electrical values of voltage, current, and resistance.

Network Performance Baseline Documentation

Documentation that records the performance of a network before changes are made. This measurement helps establish the effect a change may have, both good and bad.

Hardware Faults Problem

Faulty or corrupt NIC driver files, bad cabling, or grounding problems can cause network transmission errors such as late collisions, short frames, and jabber.

Bottom-Up Troubleshooting Approach

Good approach to use when the problem is suspected to be a physical one.

Cable Testers

Handheld devices are designed for testing the various types of data communication cabling.

Analyze Information (Step 3 of 7)

Identify possible causes using network documentation, network baselines, knowledge bases, and peers.

Selection Of Transport Layer Protocol Misconfiguration

It is important that only the correct transport layer protocol be specified in an ACE.

Noise Problem

Local electromagnetic interference (EMI) can be generated by many sources, such as crosstalk, nearby electric cables, large electric motors, FM radio stations, police radio, and more.

Cabling faults Problem

Look for damaged cables, improper cable, and poorly crimped connectors. Suspect cables should be tested or exchanged with a known functioning cable.

Uncommon Protocols Misconfiguration

Misconfigured ACLs often cause problems for protocols other than TCP and UDP.

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.

Cable Analyzers

Multifunctional handheld devices used to test and certify copper and fiber cables.

Address Mapping Errors

Occurs when Layer 2 and Layer addressing is not available.

Encapsulation Errors

Occurs when bits placed in a field by the sender are not what the receiver expects to see.

Eliminate Possible Causes (Step 4 of 7)

Progressively eliminate possible causes to eventually identify the most probable cause.

Gather Information (Step 2 of 7)

Targets (i.e., hosts, devices) are identified, accessed, and information gathered.

Portable Network Analyzers

Specialized device used for troubleshooting switched networks and VLANs.

Divide-and-Conquer Troubleshooting Approach

Start at a middle layer (i.e, Layer 3) and tests in both directions from that layer.

Educated guess Troubleshooting Approach

Success of this method varies based on your troubleshooting experience and ability.

CPU Overload Problem

Symptoms include processes with high CPU utilization percentages, input queue drops, slow performance, SNMP timeouts, no remote access, no DHCP services, Telnet, and pings are slow or fail to respond.

Order Of Access Control Entries Misconfiguration

The entries in an ACL should be from specific to general.

Use Of The Established Keyword Misconfiguration

The established keyword applied incorrectly, can provide unexpected results.

Implicit Deny Any Misconfiguration

The implicit ACE can be the cause of an ACL misconfiguration.

Troubleshooting

The process of analyzing a design problem and finding a way to fix it.

Top-Down Troubleshooting Approach

Use this approach for simpler problems, or when you think the problem is with a piece of software.

Follow-the-Path Troubleshooting Approach

Used to discover the actual traffic path from source to destination to reduce the scope of troubleshooting.

Define the Problem (Step 1 of 7)

Verify that there is a problem and then properly define what the problem is.

Solve the Problem (Step 7 of 7)

When solved, inform all involved and document the cause and solution to help solve future problems.

Propose Hypothesis (Step 5 of 7)

When the most probable cause has been identified, a solution must be formulated.

Substitution Troubleshooting Approach

You physically swap a suspected problematic device with a known, working one.