思科认证考试（ＣＣＮＡ）考试模拟题６０—７１及答案

CCNA试题60-71答案

60. [RINx] What condition does Serial 0 down & protocol up represent? 

a) The interface is disconnected but keep alives are being received 
b) The interface is working properly but keep alives are not being received 
c) The interface is bad and should be replaced 
d) The interface is working correctly. 
e) Condition not possible 

Answer 
e) Condition not possible 

The down and up combination is not legal 

Let’s review all the possibilities: 

Serial 0 down & line protocol down 
Serial 0 administratively down and line protocol down 
Serial 0 up and protocol down 
Serial 0 up and protocol down (looped) 
Serial 0 up and protocol up 

Serial 0 up and protocol up - is a fully working link which means that both the interface and the line protocol have successfully initialized and protocol keep alives are being received. 

Serial 0 administratively down - and line protocol down this condition indicates that a shut command has been configured on this interface, to reverse this condition execute a no shut command 

Serial 0 up and protocol down (looped) - this condition indicates that this interface is receiving it’s own keep alives which is a result of putting a CSU/DSU in loopback mode. 

Serial 0 down & line protocol - down this means that carrier detect signal (DCD) is not being received. You might want to make a call to your carrier to see if the local loop is up!! 

Serial 0 up and protocol down - if a interface has detected a large number of errors during a keep alive period which could be caused by a defective CSU/DSU. 



61.[CxNx] What command correctly displays the running configuration file? 

a) show configuration 
b) show running-configuration 
c) show active-configuration file 
d) write terminal 
e) all of the above 

Answer 
b) show running-configuration 
d) write terminal 

Many times in class some students who have some experience with older versions are familiar with the show configuration command and do not realize that this command shows the start-up configuration. 

Usually they have made a change to the running-configuration. Then they issue the show configuration command and they think something is wrong with the router because the change doesn’t show up. 

Since version 10.3, the command show running-configuration will display the running configuration command. Prior to this version, write terminal was the appropriate command. 

In general many of the 10.3 and later commands are intuitive such as: 

show run 
show start 
copy run start 
copy start run 

What may not be intuitive is that when a copy is made to the running-configuration this is not the same as a DOS type copy - in other words the original running configuration is not lost. The resulting running configuration file is a blending of the two files. 

62. [RINx] What is the purpose of TTL? 

a) Prevent routing loops 
b) Prevents Timely Telnet Losses 
c) Remind engineers that life is short 
d) To prevent IP datagrams from living long and fruitful lives 
e) To prevent IP datagrams that are caught in a routing loop from traversing the network forever. 

Answer 
e) To prevent IP datagrams that are caught in a routing loop from traversing the network forever. 

Time To Live is how long a packet can survive on the network before it will be removed. Each host on the net should decrement the time TTL by one. 

Usually 255 on an ethernet segment 

The logan’s run effect! 

63. [RINx] Which should be the subnet mask for a class C address if 62 hosts are required? 

a) 255.255.255. 192 
b) 255.255.192.0 
c) 0.0.0.192 
d) 255.255.255.62 
e) none of the above 

Answer 
a) 255.255.255.192 

To calculate the number of host or networks using the formula 2 to the nth degree - 2 where the nth degree is the number of bits that will be used to describe the host or the network. 

To answer this question we first have to determine how many host bits would we need to have at least 62 unique combinations. 

Using our formula we need to have 6 host bits 2 to the 6th power - 2 = 62 

This would leave us with 2 network bits therefore the mask is 192 in the fourth octet. 

64. [CxNx] After the configuration command is used, when does it become effective? 

a) immediately 
b) after the router is rebooted 
c) after you exit the configuration mode 
d) depends on the change that is made 
e) All of the above 

Answer 
a) immediately 

There are times when the router needs to be bounced, but it is very rare.