CCNA 200-125 Troubleshooting

Best command to test Autonegotiation?

show interfaces status

A port can be err-disabled for which reasons?

*BPDU guard violation *Flapping interface *Misconfigured EtherChannels *Duplex Mismatch *ARP inspection *DHCP snooping *Port security violation *Hardware issued (wrong modules or cables) *Late-collision detection *UniDirectional Link Detection (UDLD) *Inline power issues

What are Input Errors Interface Counters?

A total of many counters, including runts, giants, no buffer, CRC, frame, overrun, and ignored counts.

What are Collisions Interface Counters?

Counter of all collisions that occur when the interface is transmitting a frame.

What are CRC Interface Counters?

Cyclic Redundancy Check interface counters count the received frames that did not pass the FCS math; can be caused by collisions.

What is the second part of Step 1 in the Troubleshooting process after Problem Isolation?

Documentation. It works best when the person troubleshooting the problem documents what they find, typically in a problem tracking system.

What is the most common cause of interface errors?

Duplex Mismatch

What is the second part of Step 2 in the Troubleshooting process if you cannot resolve the problem?

Escalation. Most companies have a defined escalation process, with different levels of technical support and management support depending on whether the next step requires more technical expertise or management decision making.

What is the first step in solving a routing protocol problem?

Examine the internetwork design to determine on which interfaces the routing protocol should be enabled and which routers are expected to become neighbors.

What are Runt Interface Counters?

Frames that did not meet the minimum frame size requirement (64 bytes, including the 18-byte destination MAC, source MAC, type, and FCS). Can be caused by collisions.

What are Giant Interface Counters?

Frames that exceed the maximum frame size requirement (1518 bytes, including the 18-byte destination MAC, source MAC, type, and FCS).

How can you diagnose Late Collisions due to a Duplex Mismatch?

Keep repeating the show interfaces command, and if you see the late collisions counter incrementing on a half-duplex interface, check the link.

Troubleshooting resolves around what three big ideas?

Predicting what should happen, determining what is happening that is different than what should happen, and figuring out why that different behavior is happening.

What is the first part of Step 1 in the Troubleshooting process?

Problem isolation. Problem isolation is the process of taking what you know about a possible issue, confirming that there is a problem, and determining which devices and cables could be part of the problem, and which ones are not part of the problem.

What are Frame Interface Counters?

Received frames that have an illegal format, for example, ending with a partial byte; can be caused by collisions.

What is the first part of Step 2 in the Troubleshooting process before Escalation?

Resolve. Problem isolation should eventually uncover the root cause of the problem—that is, the cause which, if fixed, will resolve the problem. In short, resolving the problem means finding the root cause of the problem and fixing that problem.

What are Late Collisions Interface Counters?

The subset of all collisions that happen after the 64th byte of the frame has been transmitted. (In a properly working Ethernet LAN, collisions should occur within the first 64 bytes; late collisions today often point to a duplex mismatch.)

What are Packets Output Interface Counters?

Total number of packets (frames) forwarded out the interface.

What are Output Errors Interface Counters?

Total number of packets (frames) that the switch port tried to transmit, but for which some problem occurred.

What is the third and final step in the troubleshooting process??

Verify or monitor: You hear of a problem, you isolate the problem, document it, determine a possible root cause, and you try to resolve it. Now you need to verify that it really worked. In some cases, that may mean that you just do a few show commands. In other cases, you may need to keep an eye on it over a period of time, especially when you do not know what caused the root problem in the first place.

What is the third step in solving a routing protocol problem?

Verify that each router has formed all expected neighbor relationships. If it hasn't, find the root cause and fix the problem.

What is the second step in solving a routing protocol problem?

Verify whether the routing protocol is enabled on each interface (as per Step 1). If it isn't, determine the root cause and fix the problem.