Block cipher and a stream cipher

What is the difference between a block cipher and a stream cipher?

What are the two general approaches to attacking a cipher?

List and briefly define types of cryptanalytic attacks based on what is known to the attacker.

1.The command ntp server 10.1.1.1 is issued on router R1. What impact does this command have?

A. Identifies the NTP server that R1 will use to send system log messages to

B. Identifies the NTP server that R1 will use to store backup configurations

C. Identifies R1 as the NTP server using IP address 10.1.1.1

D. Synchronizes the clock of R1 with the timeserver at IP address 10.1.1.1

2. Which two statements are true about NTP servers in an enterprise network? (Choose two.)

A. All NTP servers synchronize directly to a stratum 1 time source.

B. NTP servers at stratum 1 are directly connected to an authoritative time source.

C. NTP servers control the mean time between failures (MTBF) for key network devices.

D. NTP servers ensure an accurate time stamp on logging and

debugging information.

E. There can be only one NTP server on an enterprise network.