200-301 CCNA practice questions: IP Services

D is correct. Topic 4.9. RFC 1350 defines TFTP over UDP with the server listening on the well-known port 69, and the protocol carries no user authentication at all, which is why TFTP servers are usually opened only for the duration of a transfer. Cisco's file transfer guide describes FTP as a standard network protocol used to transfer files over a TCP-based network, requires a valid username and password for the remote server, and warns that FTP transfers data and credentials in plaintext and should not be used for sensitive information over untrusted networks; the client side needs TCP port 21 for control plus data ports. Devices store the credentials with ip ftp username and ip ftp password.
↗ Cisco 200-301 CCNA v1.1 Exam Topics — Section 4: IP Services

B is correct. Topic 4.1. Cisco documents the three pieces that have to line up: ip nat pool names the usable global addresses, ip nat inside source list ... pool ... overload translates the addresses matched by the access list, and the interfaces are marked with ip nat inside and ip nat outside. The guide explains the overload keyword as the one that allows multiple inside devices to be translated to the same valid IP address, which is port address translation: the inside local addresses are replaced by one inside global address and the translation table keeps the sessions apart by port. A pool whose first and last address are identical is the standard way of writing that in a pool-based configuration.
↗ Cisco 200-301 CCNA v1.1 Exam Topics — Section 4: IP Services

D is correct. Topic 4.2. Cisco describes the stratum as how many NTP hops away a machine is from an authoritative time source: a stratum 1 time server has a radio or atomic clock directly attached to it, it then sends its time to a stratum 2 time server through NTP, and so on, so each device that takes its time from a server sits one stratum below that server. The ntp master [stratum] command configures the Cisco IOS software as an NTP master clock to which peers synchronize themselves when an external NTP source is not available; the stratum argument runs from 1 to 15 and defaults to 8, and the software clock must have been set from some source, including manual setting, before the command has any effect. Cisco also cautions that valid time sources can be easily overridden with this command, especially if a low stratum number is configured. A client association toward a remote source is configured with ntp server instead, and NTP runs over UDP port 123.
↗ Cisco 200-301 CCNA v1.1 Exam Topics — Section 4: IP Services

B is correct. Topic 4.6. Cisco defines a DHCP relay agent as a Layer 3 device that forwards DHCP packets between clients and servers, and explains that relay agents forward requests and replies when the client and server are not on the same physical subnet. The relay function is enabled with the ip helper-address command on the interface where the client broadcasts arrive. The documentation adds the detail that makes address selection work: the relay agent inserts the IP address of the interface containing the ip helper-address command into the gateway IP address (giaddr) field of the DHCP packet, which enables the DHCP server to determine which subnet should receive the offer and identify the appropriate address range.
↗ Cisco 200-301 CCNA v1.1 Exam Topics — Section 4: IP Services

A is correct. Topic 4.7. Cisco's comparison of the two rate-limiting tools states that policing drops or re-marks excess packets over the committed rate and does not buffer, while shaping buffers and queues excess packets over the committed rate, so the result of traffic shaping is a smoothed packet output rate whereas policing propagates bursts. The guide lists the typical direction as outbound for shaping and inbound or outbound for policing, and names the tradeoff: shaping can introduce delay because of queuing, policing drops packets and throttles TCP windows. A shaper is described as a policer with a queue, which is the one-sentence version of the difference.
↗ Cisco 200-301 CCNA v1.1 Exam Topics — Section 4: IP Services