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Frequently Asked Questions



Explanations

Questions
1-9 | 10-14

10. [xINx] The way that TCP uses acknowledgements is best referred to as: (Choose one.)

a) Expectational
b) Sequential
c) Current
d) Sliding
e) Incremental

Answer
a) Expectational

TCP uses expectational acknowledgements, meaning that the acknowledgement number refers to the packet which is expected next. For instance, assume that the sender had just sent segments 12, 13 and 14. If the receiver receives all three of these segments correctly, the receiver would ack 15. This means the receiver is acknowledging the correct receipt of segments 12, 13 and 14 and now expects to receive segment 15 next.

Refer to the captures below:

Based on the above capture the receiver of the above packet would ACK with 1891894734.

Refer to the next capture:

 

11. [xINx] Which of the following would most likely use the protocol UDP? (Choose four.)

a) DNS
b) FTP
c) TFTP
d) TELNET
e) SNMP
f) NFS
g) SMTP

Answer
a) DNS
c) TFTP
e) SNMP
f) NFS

The following is a capture of a TFTP.

 

12. [xINx] The protocol IP is best described as: (Choose one.)

a) Determines the data link address for known MAC addresses
b) Determines network addresses when data link addresses are known
c) Provides connectionless, best effort delivery routing of datagrams
d) Provides connection oriented, reliable delivery of datagrams
e) Provides connection oriented, best effort delivery routing of datagrams

Answer
c) Provides connectionless, best effort delivery routing of datagrams

 

 

13. [xINx] The protocol ICMP is best described as: (Choose one.)

a) Helps IP by determining the data link addresses for known IP addresses
b) Resolves MAC addresses to IP addresses
c) Resolves IP addresses to MAC addresses
d) Adds a reliable connection-oriented service to IP
e) Helps IP by providing control and messaging capabilities

Answer
e) Helps IP by providing control and messaging capabilities

ICMP is used for echo requests and echo replies. Here is a capture of a successful ping:

ICMP echo request:

ICMP echo reply:

 

14. [xINx] What two protocols would be needed to send a host unreachable message to a source host? (Choose two.)

a) IP
b) ARP
c) FTP
d) ICMP
e) RARP
f) SNMP

Answer
a) IP
d) ICMP

ICMP is a helper protocol for IP to deliver messages. Some ICMP messages are Destination Unreachable, Source Quench, Echo and Address Request. Each of these ICMP messages is carried in IP datagrams.

 

Questions
1-9 | 10-14

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