M844: Network Troubleshooting Flashcards
The headquarters facility of your company has abruptly lost connectivity to the private WAN. You know there were some people installing a new power outlet next to the rack where the WAN Edge router is located, so you suspect the cause is that the WAN Edge router has been accidentally powered off. What is the next step to troubleshooting the outage?
A. Identify the problem
B. Establish a theory of probably cause
C. Test the theory to confirm if it is true
D. Establish a plan for problem resolution
C. Test the theory to confirm if it is true
Explanation: In this case the problem has already been identified as a loss of connectivity to the WAN and you reflected on a recent change where people were working on the power outlet being the WAN Edge Router rack. So, you have established a theory of probable cause being that it could be the WAN Edge
Router has been powered off. The next step is to test the theory to confirm that the WAN Edge Router did indeed loose power. This would be done by going over to the rack where the WAN Edge Router is located and checking the power source. After you have confirmed the power source is bad you would then
establish a resolution plan which would be to connect the router to a known good power source. After that you would implement your solution to restore power to the router, then verify the router boots up properly and system functionality is restored. After everything is restored you would then need to document that the router has been moved to a new power source and identify the bad power source that needs to be fixed.
After receiving a problem report you talk to the users and figure out exactly what symptoms they are having. What is the next question you should ask yourself and your IT team?
A. What was the last thing that changed?
B. How many users are affected?
C. What exactly is the problem?
D. Can we duplicate the issue?
A. What was the last thing that changed?
Explanation: As part of identifying the problem you get started by gathering information about the problem and trying to duplicate it if possible. Then you questions users to find out how many people are affected and what the actual symptoms are. Once you have this information you should ask the question:
What was the last thing that change? With a little knowledge about what happened and who was affected you may be able to relate the problem with a recent change that occurred on the network. A lot of times this gets you directly to the cause and solution right away.
A user reports that they cannot connect to the network. You make your way to the user’s workstation and you see that a message continuously pops up on the screen that states “duplicate IP address detected”. This means the IP address on the workstation is conflicting with another IP address on the network and therefore the workstation is not able to consistently communicate with the network. At which layer of the OSI model does this problem reside?
A. Layer 1
B. Layer 2
C. Layer 3
D. Layer 4
C. Layer 3
Explanation: Layer 3 is the Network Layer and is where IP, routing, and IP addresses are referenced. A duplicate IP address is an IP conflict and to resolve it the user’s workstation would need to be reconfigured with a different IP address in the TCP/IP settings. If the user’s workstation is not the source of the actual problem then the node that is producing the conflict would need to be tracked down and isolated.
You manage a network that has a Voice over IP phone system and has a voice VLAN that all the VoIP phones connect into. You install a new VoIP phone, it powers on via PoE over the LAN cable, but it receives an IP address that is not from the Voice network and it cannot connect to the phone system server. What is the most likely cause of this problem.
A. The phone has a power issue
B. The network cable is bad and needs to be tested
C. The DHCP server is misconfigured
D. The phone is connected to the wrong VLAN
D. The phone is connected to the wrong VLAN.
Explanation: If the phone is able to receive power via PoE from the switch and pull an IP address via DHCP then most likely there not a problem with the LAN cable, the phone power, or the DHCP server. In this case the phone is getting an IP address from a different network than the Voice network. The only way this
could happen is if the phone is connected to a network other than the Voice network. Since the company uses a Voice VLAN the problem is most likely that the phone is connected to a port on the switch that is not assigned to the Voice VLAN. To correct the issue you would connect to the switch and assign the
switchport to the correct VLAN.
A traceroute reveals a network node cannot be reached and the traceroute fails after 3 hops. This is an example of identifying an end-to-end connectivity problem.
A. True
B. False
A. True
Explanation: An end-to-end connectivity problem is simply when one node is unable to be reached by another node. To troubleshoot this type of problem use the divide & conquer (aka half-split) method. Traceroute, ping, and pathping are the best tools for identifying where the problem resides from end-toend. Once the problem area has been defined then you are able to being looking into the actual cause of the connectivity problem whether it a bad cable, missing IP route, issue with the host computer or another network node, etc.
