思科认证考试（ＣＣＮＡ）考试模拟题７２—７８及答案

CCNA试题72-78答案

72. [xINx] The size of a window in a TCP segment establishes what? (Choose one.) 

a) The maximum number of bytes that a single frame may not exceed 
b) The allowable bandwidth for this TCP session 
c) The number of octets that the receiver must be willing to accept 
d) The number of 32-bit words in the header 
e) The number of octets that the sender is willing to accept 

Answer 
e) The number of octets that the sender is willing to accept 

73. [xINx] Which protocols are best described as connection-oriented and reliable? (Choose two.) 

a) UDP 
b) IP 
c) TCP 
d) IPX 
e) TCP over IP 
f) UDP over IP 

Answer 
c) TCP 
e) TCP over IP 

This question is meant to be a little tricky. TCP is layer 4, which uses IP at layer 3. 

74. [xINx] A Telnet session to a remote host would be addressed to what port number at the remote host? (Choose one.) 

a) UDP port 53 
b) TCP port 53 
c) UDP port 21 
d) TCP port 21 
e) UDP port 161 
f) TCP port 23 

Answer 
f) TCP port 23 

In the capture below NetXray interpolates the data and shows a source port of 1074 to a destination port of telnet. Refer to the data below the highlighted portion. 0x17 is 1*161 + 7* 160 = 23. 

75. [xINx] TCP "source" port number(s): (Choose the one that best describes.) 

a) Depends on the application being accessed on the destination host. 
b) Depends on the application running on the source host. 
c) Are usually assigned by the source host, and are typically some number greater than 1023. 
d) Are assigned by the source host and are usually one of the "well known" port numbers. 
e) Must be negotiated by the sender and receiver during session setup. 

Answer 
c) Are usually assigned by the source host, and are typically some number greater than 1023. 

The source port in the following capture is 1074: 

76. [xINx] In a TCP acknowledgment, the ack number refers to: (Choose one.) 

a) A sequential number beginning with 1, and incremented by 1 with each exchange, that identifies this exchange of packets as being complete 
b) The number of the packet expected next 
c) The number of the packet expected next, plus 1 
d) A number agreed upon at session establishment, which will be used by the receiver to indicate a successful exchange of packets 
e) TCP does not use acknowledgments. 

Answer 
b) The number of the packet expected next 

This number is the previous Sequence number +1. 

Check out the sequence and the acknowledgement numbers below: