思科认证考试（ＣＣＮＡ）考试模拟题０１—１９及答案

     

Answer
b) multiple stations listen for traffic and transmit at the same time

Collisions is a term that is used in an ethernet environment. Ethernet can be described as a listen then transmit scenario. First a station will listen for traffic if no traffic is sensed then a transmission will take place. If two stations transmit at the same time collisions will occur. The first station to detect the collision sends out a jamming signal to alert all stations a collision has occurred. At this point these stations set up a random interval timer when the timer expires re-transmission will occur.

Token ring is a token passing process a station can transmit only when he has the token. There never can be multiple tokens on the ring. Early token release allows up to two data frames to be transmitted on a token ring LAN at the same time. Collisions do not occur on a token ring.

Because of the point to point nature of serial links collisions do not occur.

Beaconing is a term used in a token passing environment.



12. [RINx] How many subnets are possible with a Class C address and a subnet mask of 255.255.255.252?

a) 32
b) 30
c) 60
d) 62
e) 4

Answer
d) 62

The above mask is using 6 bits to describe subnets. The formula used to determine the number of subnets (not including the all 0’s or all 1’s subnet) is 2n - 2 were n is the number of subnet bits. This is the number to use when configuring a ip address with the setup dialog.



13. [RxNx] What commands will list all protocols that are currently being routed? (Choose all that apply.)

a) show ip protocol
b) show protocol
c) show run
d) show start
e) All of the above

Answer
b) show protocol
c) show run

Show ip protocol will show just the ip routing protocols that are currently configured. Show start may or may not show the current routed protocols.

Below is the output of show protocol

Router_B#show protocol
Global values:
Internet Protocol routing is enabled
Appletalk routing is enabled
BRI0 is administratively down, line protocol is down
BRI0:1 is administratively down, line protocol is down
BRI0:2 is administratively down, line protocol is down
Serial0 is administratively down, line protocol is down
Serial1 is administratively down, line protocol is down
Serial2 is administratively down, line protocol is down
Serial3 is administratively down, line protocol is down
TokenRing0 is administratively down, line protocol is down

14. [xxNx] Which of the following are true of access lists?

a) Access list should have at least one permit statement.
b) The last configured line should always be a permit statement.
c) Every access-list will implicitly deny all traffic.
d) Access-lists are processed top down.
e) All of the above.

Answer
e) All of the above.

Every access list has an implicit deny all at the end. What would the need be to create a access list with just deny statements. Access-list are processed from the top down therefore the order of each statement could be critical, for instance suppose you created an access list and the first line was a permit any and the next line was a deny. Since it’s top down processing a packet would be permitted to pass on the first line and the second line would never be executed. An extended list will give you a "match count" that will help in determining what the most efficient order should be.

15. [xxNx] If the access-group command is configured on an interface and there is no access-list created which of the following is most correct?

a) An error message will appear.
b) The command will be executed and deny all traffic out.
c) The command will be executed and permit all traffic out.
d) The command will be executed and permit all traffic in and out.
e) The command will be executed and deny all traffic in and out.

Answer
d) The command will be executed and permit all traffic in and out.