killtest 支新招，助你轻松过640-821

640-821是CCNA认证考试的一项科目，众所周知对于一个职场人员，拥有一张认证考试证书，对我们的升职有着很大的作用。在这里不多说，只是想说明一下，本来从网上拉了一些题库资料，据说很有作用，需要的朋友过来看看。

1. Refer to the exhibit. Why was this message received?
A. No VTY password has been set.
B. No enable password has been set.
C. No console password has been set.
D. No enable secret password has been set.
E. The login command has not been set on CON 0.
F. The login command has not been set on the VTY ports.
Answer: A

2. A network administrator needs to create 29 subnetworks while maximizing the number of host addresses available on each subnet. How many bits must be borrowed from the host field of the network address to provide the required number of subnets with the most hosts per subnet?
A. 2
B. 3
C. 4
D. 5
E. 6
F. 7
Answer: D

3. Refer to the exhibit. If host A sends an IP packet to host B, what will the OSI Layer 3 source address be
in the packet when it reaches host B?
A. 10.168.10.99
B. 10.168.11.88
C. 10.168.11.65
D. A1:A1:A1:A1:A1:A1
E. B2:B2:B2:B2:B2:B2
F. C3:C3:C3:C3:C3:C3
Answer: A

4. What is the difference between the Cisco router IOS commands show cdp neighbor detail and show cdp entry?
A. The show cdp neighbor detail command shows all neighbor information, while show cdp entry displays only one line of output for each neighbor.
B. The show cdp entry command shows neighbor information for specific neighbors only, while show cdp neighbor detail lists each neighbor with detailed output on each.
C. The show cdp entry command shows neighbor information for all neighbors with one line of output for each, while show cdp neighbor detail lists each neighbor with detailed output on each.
D. The show cdp neighbor detail command shows neighbor information for a single neighbor only, while show cdp entry displays detailed output on each neighbor known.
Answer: B

5. Refer to the exhibit. A person is trying to send a file from a host on Network A of the JAX Company to a server on Network Z of the XYZ Company. The file transfer fails. The host on Network A can communicate with other hosts on Network A. Which command, issued from router RTA, would be the most useful for troubleshooting this problem?
A. show flash:
B. show history
C. show version
D. show interfaces
E. show controllers serial
Answer: D

6. Which Layer 4 protocol is used for a Telnet connection?
A. IP
B. TCP
C. UDP
D. ICMP
E. DNS
Answer: B

7. What is the subnet address of 172.16.159.159/22?
A. 172.16.0.0
B. 172.16.128.0
C. 172.16.156.0
D. 172.16.159.0
E. 172.16.159.128
F. 172.16.192.0
Answer: C

8. What is the purpose of flow control?
A. to ensure data is retransmitted if an acknowledgment is not received
B. to reassemble segments in the correct order at the destination device
C. to provide a means for the receiver to govern the amount of data sent by the sender
D. to regulate the size of each segment
Answer: C
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