CCNA FAQ: VLSMs, Summarization, and Troubleshooting TCP/IP

CCNA FAQ: VLSMs, Summarization, and Troubleshooting TCP/IP

Q1. On a VLSM network, which mask should you use on point-to-point WAN links in order to reduce the waste of IP addresses?
A. /27
B. /28
C. /29
D. /30
E. /31

Answer: D. A point-to-point link uses only two hosts. A /30, or 255.255.255.252, mask provides two hosts per subnet.

Q2. In the network shown in the diagram, how many computers could be in subnet B?
ccna-faq-vlsms-summarization-troubleshooting-tcpip2
A. 6
B. 12
C. 14
D. 30

Answer: C. Using a /28 mask, there are 4 bits available for hosts. Two to the fourth power minus 2 = 14.

Q3. In the diagram below, in order to have as efficient IP addressing as possible, which network should use a /29 mask?
ccna-faq-vlsms-summarization-troubleshooting-tcpip3
A. A
B. B
C. C
D. D

Answer: D. For 6 hosts we need to leave 3 bits in the host portion since 2 to the third power = 8 and 8 less 2 is 6.With 3 bits for the host portion, that leaves 29 bits for the mask or /29.

Q4. To use VLSM, what capability must the routing protocols in use possess?
A. Support for multicast
B. Multiprotocol support
C. Transmission of subnet mask information
D. Support for unequal load balancing

Answer: C. To use VLSM, the routing protocols in use possess the capability to transmit subnet mask information

Q5. What summary address would cover all the networks shown and advertise a single,
efficient route to Router B that won’t advertise more networks than needed?
ccna-faq-vlsms-summarization-troubleshooting-tcpip5
A. 172.16.0.0/24
B. 172.16.1.0/24
C. 172.16.0.0/24
D. 172.16.0.0/20
E. 172.16.16.0/28
F. 172.16.0.0/27

Answer: D. In a question like this, you need to look for an interesting octet where you can combine networks. In this example, the third octet has all our subnets so we just need to fid our block size now. If we used a block of 8 starting at 172.16.0.0/19, then we cover 172.16.0.0 through 172.16.7.255. However, if we used 172.16.0.0/20, then we’d cover a block of 16 which would be from 172.16.0.0 through 172.16.15.255, which is the best answer.

Q6. In the diagram below what is the most likely reason the station cannot ping outside of its network?
ccna-faq-vlsms-summarization-troubleshooting-tcpip6
A. The IP address is incorrect on E0 of the router.
B. The default gateway address is incorrect on the station.
C. The IP address on the station is incorrect.
D. The router is malfunctioning.

Answer: C. The IP address of the station and the gateway are not in the same network. Since the address of the gateway is correct on the station, it is most likely the IP address of the station is incorrect.

Q7. If Host A is configured with an incorrect default gateway and all other computers and the router are known to be configured correctly, which of the following statements is TRUE?
A. Host A cannot communicate with the router.
B. Host A can communicate with other hosts in the same subnet.
C. Host A can communicate with hosts in other subnets.
D. Host A can communicate with no other systems.

Answer: B. With an incorrect gateway, Host A will not be able to communicate with the router or beyond the router but will be able to communicate within the subnet.

Q8. Which of the following troubleshooting steps, if completed successfully, also confirms
the other steps will succeed as well?
A. ping a remote computer
B. ping the loopback address
C. ping the NIC
D. ping the default gateway

Answer: A. Pinging the remote computer would fail if any of the other tests fail.

Q9. When a ping to the local host IP address fails, what can you assume?
A. The IP address of the local host is incorrect.
B. The IP address of the remote host is incorrect.
C. The NIC is not functional.
D. The IP stack has failed to initialize.

Answer: C. When a ping to the local host IP address fails, you can assume the NIC is not functional.

Q10. When a ping to the local host IP address succeeds but a ping to the default gateway IP address fails, what can you rule out? (Choose all that apply.)
A. The IP address of the local host is incorrect.
B. The IP address of the gateway is incorrect.
C. The NIC is not functional.
D. The IP stack has failed to initialize.

Answer: C, D. If a ping to the local host succeeds, you can rule out IP stack or NIC failure.

Q11. Which of the networks in the diagram could use a /29 mask?
ccna-faq-vlsms-summarization-troubleshooting-tcpip6.jpg11
A. Corporate
B. LA
C. SF
D. NY
E. none

Answer: E. A /29 mask yields only 6 addresses, so none of the networks could use it.

Q12. What network service is the most likely problem if you can ping a computer by IP
address but not by name?
A. DNS
B. DHCP
C. ARP
D. ICMP

Answer: A. The most likely problem if you can ping a computer by IP address but not by name is a failure of DNS.

Q13. When you issue the ping command, what protocol are you using?
A. DNS
B. DHCP
C. ARP
D. ICMP

Answer: D. When you issue the ping command, you are using the ICMP protocol.

Q14. Which of the following commands displays the networks traversed on a path to a network destination?
A. ping
B. traceroute
C. pingroute
D. pathroute

Answer: B. The traceroute command displays the networks traversed on a path to a network destination.

Q15. What command generated the output shown below?
Reply from 172.16.10.2: bytes=32 time<1ms TTL=128
Reply from 172.16.10.2: bytes=32 time<1ms TTL=128
Reply from 172.16.10.2: bytes=32 time<1ms TTL=128
Reply from 172.16.10.2: bytes=32 time<1ms TTL=128
A. traceroute
B. show ip route
C. ping
D. pathping

Answer: C. The ping command tests connectivity to another station. The full command is shown below.
C:\>ping 172.16.10.2
Pinging 172.16.10.2 with 32 bytes of data:
Reply from 172.16.10.2: bytes=32 time<1ms TTL=128
Reply from 172.16.10.2: bytes=32 time<1ms TTL=128
Reply from 172.16.10.2: bytes=32 time<1ms TTL=128
Reply from 172.16.10.2: bytes=32 time<1ms TTL=128
Ping statistics for 172.16.10.2:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms

Q16. In the work area, match the command to its function on the right.

Answer:

Q17. Which of the following network addresses correctly summarizes the three networks
shown below efficiently?
10.0.0.0/16
10.1.0.0/16
10.2.0.0/16
A. 10.0.0.0/15
B. 10.1.0.0/8
C. 10.0.0.0/14
D. 10.0.0.8/16

Answer: C. The interesting octet in this example is the second octet, and it is a block size of four starting at 10.0.0.0. By using a 255.252.0.0 mask, we are telling the summary to use a block size of four in the 2nd octet. This will cover 10.0.0.0 through 10.3.255.255. This is the best answer.

Q18. What command displays the ARP table on a Cisco router?
A. show ip arp
B. traceroute
C. arp -a
D. tracert

Answer: A. The command that displays the ARP table on a Cisco router is show ip arp.

Q19. What switch must be added to the ipconfig command on a PC to verify DNS configuration?
A. /dns
B. -dns
C. /all
D. showall

Answer: C. The /all switch must be added to the ipconfig command on a PC to verify DNS confiuration.

Q20. Which of the following is the best summarization of the following networks:
192.168.128.0 through 192.168.159.0
A. 192.168.0.0/24
B. 192.168.128.0/16
C. 192.168.128.0/19
D. 192.168.128.0/20

Answer: C. If you start at 192.168.128.0 and go through 192.168.159.0, you can see this is a block of 32 in the third octet. Since the network address is always the fist one in the range, the summary address is 192.168.128.0. What mask provides a block of 32 in the third octet? The answer is 255.255.224.0, or /19.

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