思科认证考试（ＣＣＮＡ）考试模拟题２０—３９及答案

    
 
36. [SxNx] The following statement would deny traffic from what subnets? 

Router_B(config)#access-list 101 deny 

tcp 10.1.8.0 0.0.7.255 

192.16.5.0 0.0.0.255

a) 10.1.8.0 
b) 10.1.15.0 
c) 10.1.0.0 
d) 10.1.16.0 
e) choice a and b 

Answer 
a) 10.1.8.0 
b) 10.1.15.0 
e) choice a and b 

The type of mask used here is an inverse mask meaning that when the mask has a bit value of 0 the access list must match the corresponding bits. If the inverse mask has a value of 1 it s "don t care," meaning the access list does not care about the corresponding bit. 

Since the inverse mask has a value of 0 in the first and second octet the access list must match the first 16 bits. Since the value of the fourth octet is 255 that means all the bits are ones, so the access list does not care about the value of the fourth octet. 


10 1 8 0 
0 0 7 255 

The octet that is not so obvious is the third octet. The inverse mask of 7 gives us 0 s for the most significant 5 bits and 1 s for the last 3. Refer to the chart below. 

Since the least 3 significant bits are 1 s they can be anything, which gives us the subnets 8-15. 

37. [SxNx] Name three reasons why VLAN s should be created. 

a) Moves, Adds and Changes are made simpler. 
b) There is less administrative overhead. 
c) The switch can route between VLANS. 
d) It limits broadcasts domains. 
e) The router can switch faster. 

Answer 
a) Moves, Adds and Changes are made simpler. 
b) There is less administrative overhead. 
d) It limits broadcasts domains. 

If a workstation moves there is a good chance the move is within the same VLAN. If we have a good design of a single subnet within each VLAN there will be no need to reconfigure the workstation with a new layer 3 address. Each VLAN defines a broadcast domain. 

38. [SxNx] The Catalyst 5000 uses which switching mode? 

a) Cut-through 
b) Store and forward 
c) Fast switching 
d) Choice a and b 
e) Choice a and c 

Answer 
b) Store and forward 

Store and forward mode receives the complete frame before forwarding takes place. After the destination and source addresses are read the cyclic redundancy check is performed, the frame is forwarded. Switch latency is dependent upon frame size. 

Cut-through, on the other hand, starts forwarding the frame as soon as the destination address is read. This mode reduces latency in the switch. 

39. [OxNx] Which of the following layers defines data representation? 

a) Application Layer 7 
b) Presentation Layer 6 
c) Session Layer 5 
d) Transport Layer 4 
e) Network Layer 3 
f) Data Link Layer 2 
g) Physical Layer 1 

Answer 
b) Presentation Layer 6