1,001 CCNA Questions Chapter 12: Troubleshooting Network Communication
B. show cdp neighbors detail Of the commands listed, only the show cdp neighbors detail command displays a list of neighboring devices and their IP addresses.
Which of the following commands can you use to figure out the IP address of a neighboring router? (A) show cdp neighbors (B) show cdp neighbors detail (C) show cdp (D) cdp run
D. no debug all When you disable debugging, use the no debug all command so that you can be sure that all levels of debugging are disabled. Debugging places extra processing load on the router, which means you do not want it running if it is not needed.
Which of the following commands is recommended to disable debugging? (A) no debug ip all (B) no debug ip nat (C) no debug ip rip (D) no debug all
B. The network media is attached at both ends of the link D. a layer-2 protocol has been loaded and configured at either end of the link. If the link light on an interface displays green, it indicates that a physical connection is established between the two points, and a data link protocol is configured at either end.
Having a green link light indicates that which of the following conditions have been met? (Select two.) (A) A layer-3 protocol has been assigned at either end of the link. (B) The network media is attached at both ends of the link. (C) The IP address on the interface has been configured. (D) A layer-2 protocol has been loaded and configured at either end of the link.
A. show ip arp D. show arp The show ip arp command and the show arp command can be used to view the ARP cache on a Cisco router. The show ip arp command only displays mac addresses that map to the IP Layer 3 protocol, while show arp will display all mac addresses for all Layer 3.
How do you view your ARP cache on a Cisco router? (Select two.) (A) show ip arp (B) arp -a (C) arp -show (D) show arp
C. no shutdown If an interface is shown as administratively down, try to bring the interface up by using the no shutdown command on the interface.
If an interface shows as administratively down, what command do you use to bring the interface up? (A) up (B) enable (C) no shutdown (D) no down
B. R1 The ARP request would be sent to router R1 because that is the device Computer A needs to send the data to in order to have the data leave the network.
Looking at the figure below, Computer A is initiating communication to Computer B and sends out an ARP request. Which device responds with the ARP reply message? (A) SW1 (B) R1 (C) R2 (D) Computer B
B. 6 A runt is a packet that is smaller than the allowable size for the network. With Ethernet networks, that is 64 bytes. Looking at the figure, you can see that there are 6 runt messages received. Runt could be due to collisions or a malfunctioning network card sending garbage packets out on the network.
Looking at the output in the figure below, how many packets have been received that were less than 64 bytes? (A) 3 (B) 6 (C) 87 (D) 216,380
A. DCE Looking at the output in the figure, you can see that the serial port on the router is configured as the data communication equipment ( DCE). The other end of the point-to-point link would be the opposite, data terminal equipment (DTE).
Looking at the output in the figure below, what end of the point-to-point link is Serial0/2/0? (A) DCE (B) DTE (C) MPC8600 (D) PowerQUICC
B. 64 Kbps You can view the clock rate on a serial link DCE link when using the show controllers command. Note that the clock rate is set to 64000, or 64 Kbps.
Looking at the output in the figure below, what is the clock rate of serial0/2/0? (A) 35 Kbps (B) 64 Kbps (C) 128 Kbps (D) 860 Kbps
D. 0010.11d9.d001 When looking at the output for the command, you can see that FastEthernet0/0 has the IP address of 23.0.0.1 and its hardware address is 0010.11d9.d001.
Looking at the output of the show interfaces command seen in the figure below, what is the MAC of the interface using the IP address 23.0.0.1? (A) HD64570 (B) ffff.ffff.ffff (C) 0010.11d9.d002 (D) 0010.11d9.d001
D. HDLC When looking at the show interfaces command, you can see that the serial port is using the encapsulation of HDLC.
Looking at the output of the show interfaces command seen in the figure below, what is the encapsulation protocol being used by the serial port? (A) CDP (B) PPP (C) STP (D) HDLC
D. FastEthernet0/1 has not been configured. Looking at the figure, you will notice that serial 0/2/0 is using HDLC and not PPP, Fast Ethernet 0/0 has an IP address assigned, and the bandwidth is 100,000 Kbits. So the only true statement when looking at the status of the interfaces is that the Fast Ethernet 0/1 has no IP address assigned and is currently down: It has not been configured.
Looking at the output of the show interfaces command seen in the figure below, which of the following statements is true? (A) Serial port is using PPP. (B) FastEthernet0/0 has no IP assigned. (C) The bandwidth of FastEthernet0/0 is 1 Gbps. (D) FastEthernet0/1 has not been configured.
What to Watch Out For Don't let common mistakes trip you up; watch for the following when working with these questions: ✓ Troubleshoot layer-1 and layer-2 characteristics of the network first when you're having connectivity issues. When troubleshooting layer 1, ensure that you are using the correct cables and that they are properly connected to the ports by checking for a link light. When troubleshooting layer 2, ensure that the data link protocol is set (Ethernet, PPP, or HDLC) and verify related settings, such as the clock rate. ✓ After verifying the physical aspect of the network, you can then check the logical aspect, such as the network layer (layer 3). When troubleshooting layer 3, verify the IP address configuration and routing table information. ✓ Ensure you know the different show commands, such as show ip route, show interfaces, show ip interface brief, and show cdp neighbors detail. Many ICND1 exam questions test your knowledge about how to troubleshoot using the show commands.
The Problems You'll Work On In this chapter, you'll review questions concerning the following topics: ✓ Using commands to help troubleshoot and diagnose network related problems ✓ Troubleshooting connectivity issues ✓ Using show commands to troubleshoot configuration issues ✓ Using debug commands to diagnose a problem
A. The pings were unsuccessful. In the figure, you can see that there are 5 periods (.), each one indicating a ping reply that was not received.
What are the results of the command executing in the figure below? (A) The pings were unsuccessful. (B) The pings were successful. (C) The traceroute was unsuccessful. (D) The ARP cache is empty.
B. show controllers serial 0/0 When troubleshooting your serial port and wanting to verify whether you have configured the interface as the DCE or DTE device, use the show controllers serial slot/ port command.
What command do you use to view whether your serial port is the DCE or DTE device? (A) show interface serial 0/0 (B) show controllers serial 0/0 (C) show ip protocols serial 0/0 (D) show serial 0/0
B. show ip arp The command is displaying the ARP cache on the Cisco device. In order to view the ARP cache, you would use the show ip arp command.
What command was used to create the output shown in the figure below? (A) show interfaces (B) show ip arp (C) show ip interface brief (D) show controllers
D. telnet In order to verify that you have configured the VTY ports successfully, you would use telnet to connect to the system.
What command would you use to test VTY port configuration? (A) traceroute (B) nslookup (C) ping (D) telnet
B. show interfaces D. show controllers Layer 1 deals with the physical aspect of the network, such as a link being present, while layer 2 of the OSI model deals with the protocol used to carry frames. The show interfaces command and show controllers command are used to troubleshoot layer 1 and layer 2.
Which of the following commands would you use to check for issues at layers 1 and 2? (Select two.) (A) show ip interface brief (B) show interfaces (C) show protocols (D) show controllers (E) show ip route
A. show ip interface brief C. show protocols E. show ip route When answering questions such as this, ask yourself what happens at layer 3 of the OSI model. The answer is the routing and logical addressing (which is handled by the IP protocol). So any commands that relate to routing or the IP protocol would be layer-3 Troubleshooting Commands. Be familiar with each of these show commands for the exam. You will need to use them in different simulators to identify the problem.
Which of the following commands would you use to troubleshoot issues at layer 3? (Select three.) (A) show ip interface brief (B) show interfaces (C) show protocols (D) show controllers (E) show ip route
A. Runt C. CRC The runt and CRC count can be viewed on an interface to determine the number of small packets received and the number of packets received that do not have the CRC information matching the calculated checksum. Both of these are an indication of collisions on the network or a bad network card sending garbage packets out on the network.
Which of the following could be an indication of excessive collisions or bad packets submitted by a malfunctioning network card? (Select two.) (A) Runt (B) Bandwidth (C) CRC (D) MTU
A. Straight-through When connecting a switch to a router, you would ensure you are using a straightthrough cable. Watch for questions on the exam that show a network diagram and ask why communication cannot occur. Sometimes you may find the wrong type of cable is being used in the diagram.
You are connecting a switch to a router. What type of cable should you use? (A) Straight-through (B) Console (C) Serial (D) Crossover
D. Crossover When connecting similar devices together, you should use a crossover cable. Watch for scenarios on the exam that describe communication issues and mention the cabling used. You may find that the wrong type of cable was used.
You are connecting two switches together. What type of cable should you use? (A) Straight-through (B) Console (C) Serial (D) Crossover
A. show ip route After you have verified the physical components and the IP addresses, you should verify that there is a route in the routing table to the destination network.
You are having trouble communicating with a remote network. You have checked the status of the interfaces: Each interface is up, and the IP addresses look fine. What command do you use next? (A) show ip route (B) show ip interface brief (C) show controllers serial 0/0 (D) show cdp
A. 23.0.0.1 The router would be the first hop in order to send data to a different, or remote, network. In this example, the first hop that a reply comes back from is 23.0.0.1, which is the router on your network.
You are testing connectivity to a system on a remote network. Using the output shown in the figure below, what is the default gateway setting of this workstation? (A) 23.0.0.1 (B) 24.0.0.2 (C) 25.0.0.10 (D) 25.0.0.1
D. Use straight-through cables to connect switches to routers. In this example, the IP address configuration is fine. The wrong cable types are being used to connect the switches to the router. You should be using straight-through cables to connect switches to routers.
You are the network administrator for a company that has users located in different offices. The network configuration is shown in the figure below. You have connected the switches to the routers with a crossover cable, and the computers to the switches with straight-through cables. Computer A cannot ping Computer B. What should you do? (A) Change the IP address of Computer A. (B) Use crossover cables to connect computers to switches. (C) Change the default gateway of Computer A. (D) Use straight-through cables to connect switches to routers.
C. Change the IP address on Computer A. In this example, the communication problem is occurring because Computer A has been configured for an invalid IP address on that network ID. A subnet mask of /27 means the increment is 32, making the network range for Computer A's network 216.83.11.64 to 216.83.11.95. The IP address assigned to Computer A is outside that range.
You are the network administrator for a company that has users located in different offices. The network configuration is shown in the figure below. You have connected the switches to the routers with a straight-through cable, and the computers to the switches with straight-through cables. Computer A cannot ping Computer B. What should you do? (A) Change the cable type connecting the switches to the routers. (B) Change the cable type connecting the computers to the switches. (C) Change the IP address on Computer A. (D) Change the IP address of Computer B. (E) Change the IP address on R1.
A. Computer B's default gateway is invalid. In this example, the IP address for the default gateway for Computer B is using the broadcast address for that network, which is invalid. You need to change the IP address of the LAN interface on router R2 and ensure computer B uses that IP address as the default gateway.
You are the network administrator for a company that has users located in different offices. The network configuration is shown in the figure below. You have connected the switches to the routers with straight-through cables, and the computers to the switches with straight-through cables. Computer A cannot ping Computer B. Why not? (A) Computer B's default gateway is invalid. (B) Computer A's default gateway is invalid. (C) A crossover was used to connect switches to routers. (D) Computer B's IP address is incorrect.
D. You are connected to a port in a different VLAN than the other system. In this scenario, the most likely cause of the problem is you have the port configured for the wrong VLAN. You will need to change the VLAN that the port is a member of.
You are the network administrator for a small network running three VLANs on a switch. You have connected a workstation to port 8 on the switch and assigned it a valid IP address for that network. You try to communicate with another system on the network, but are unable to. What could be the problem? (A) You have the wrong IP assigned. (B) CDP is running on the switch. (C) STP is blocking communication between the VLANs. (D) You are connected to a port in a different VLAN than the other system.
D. traceroute ip_address When trying to identify the point in the communication pathway that is failing, use the traceroute command, which sends you status information with each router that is hit on the way to the destination.
You are troubleshooting communication problems on a network on the other side of the country. What command do you use to identify at what point in the communication pathway there is a failure? (A) show ip arp (B) ping ip_address (C) telnet ip_address (D) traceroute ip_address
B. The pings were successful. When using the ping command on Cisco devices, five ping requests are sent out and for each reply that comes back you will see a ! on the screen. Unsuccessful pings display with a . (period).
You are troubleshooting communication to another device. What is the result of the command being executed in the figure below? (A) The pings were unsuccessful. (B) The pings were successful. (C) The traceroute was unsuccessful. (D) The ARP cache is empty.
C. 87 When looking at the show interface command, you can see the output of the interface in the last 5 minutes toward the bottom of the output. In this example, notice that there are 87 collisions on the fourth to last line of the output.
You are troubleshooting performance issues on the network and suspect that a high number of packets are being retransmitted due to collisions. You use the show interface command to view the status on the interface. Looking at the output in the figure below, how many packets have been retransmitted due to collisions? (A) 3 (B) 6 (C) 87 (D) 216,380
A. debug ip rip When troubleshooting communication problems, you can use a number of debug commands in order to see different activity on the router. In order to view rip message sent and received, you can use the debug ip rip command.
You are troubleshooting problems with RIP and suspect that your router is no longer receiving RIP updates. What command would you use to help diagnose the problem? (A) debug ip rip (B) debug all (C) no debug all (D) show interfaces
B. Enable trunking on the port connecting the switch to the router. After configuring the router with sub-interfaces, you need to ensure that you configure the port on the switch that is connected to the router as a trunk port so that it can carry the VLAN traffic.
You have a switch using multiple VLANs that is connected to a router using a straight-through cable. You have configured the router as a router on the stick. You have configured the subinterfaces on the router, but communication is not occurring between the VLANs. How do you fix the problem? (A) Use a crossover cable to connect the switch to the router on a stick. (B) Enable trunking on the port connecting the switch to the router. (C) Add static routes so the router can route between the VLANs. (D) Load RIPv2 so that routing between the VLANs can occur.
D. Verify your cable is connected properly. The first thing you should do is check the physical components of the network. Is the network cable connected to the computer properly, and to the switch properly? Do you see link lights on the computer and the switch?
You have your workstation connected to port 6 on the switch, but are unable to communicate on the network. What should you do first? (A) Use ipconfig. (B) Ping another system. (C) Check the routing table. (D) Verify your cable is connected properly.
C. Check that the data link protocol is configured. When the interface status displays as up and the protocol is down, this is an indication that the data link protocol has not been configured properly. With a serial port, check that a layer-2 protocol such as HDLC or PPP has been configured.
You receive the following output from the show interfaces command. What should you check? Serial0/2/0 is up, line protocol is down (A) Check the physical aspects of the link, such as the cable. (B) Check that the IP address is set. (C) Check that the data link protocol is configured. (D) Verify that a route is defined to the remote network.
A. Check the physical aspects of the link, such as the cable. When an interface shows a status of down and the line protocol is down, you should look to the physical (layer-1) components of the network because the line protocol will not be up unless the interface is up — meaning you don't know if the line protocol is a problem (even though it shows as down) until you fix the problem with the interface.
You receive the following output when looking at the show interfaces command. What should you check? Serial0/2/0 is down, line protocol is down (A) Check the physical aspects of the link, such as the cable. (B) Check that the IP address is set. (C) Check that the data link protocol is configured. (D) Verify that a route is defined to the remote network.
C. There is an implied deny all traffic at the end of the ACL. In this example, the access control list was created to allow telnet and SMTP traffic to pass through the router. There is an implied deny all other traffic rule at the end of the ACL, so if you expect traffic to pass through the router you must explicitly specify it.
You use the following commands to create an access control list on the FastEthernet port of the router. Users are now reporting that they cannot communicate with the intranet site. What is the problem? R1(config)# access-list 102 permit tcp any any eq 23 R1(config)# access-list 102 permit tcp any any eq 25 R1(config)# interface fastethernet0/1 R1(config-if)# ip access-group 102 in (A) The first line should not be permit. (B) The second line should not be permit. (C) There is an implied deny all traffic at the end of the ACL. (D) The ip access group command should not be used.
D. show interfaces To view the number of runt packets, which are packets too small for the network, you an use the show interfaces command.
You would like to see the number of runt packets received. What command would you use? (A) show cdp (B) show cdp neighbors detail (C) show ip interface brief (D) show interfaces
D. debug ip packet In order to view all packets being sent and received, including their details, you can use the debug ip packet command.
You would like to view the details of all packets sent or received by the router. What command would you use? (A) debug ip rip (B) debug ip route (C) debug ip ospf (D) debug ip packet
