200-301 CCNA practice questions: IP Services

Answer: D. 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. Source: Cisco 200-301 CCNA v1.1 Exam Topics - Section 4: IP Services

Answer: A. 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. Source: Cisco 200-301 CCNA v1.1 Exam Topics - Section 4: IP Services

Answer: D. Topic 4.4. Cisco's SNMP Version 3 chapter lists three security levels. noAuthNoPriv uses a username match for authentication. authNoPriv provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. authPriv provides authentication based on the same algorithms and, in addition to authentication, provides encryption of the payload. The keyword auth in snmp-server group and in snmp-server user selects the middle level, so every message is authenticated and none is encrypted, which is why a capture shows the values as text. Moving to authPriv means configuring the group with priv and giving the user a privacy key as well, for example snmp-server user poller NOC v3 auth sha Str0ngPhrase! priv aes 128 An0therPhrase!. The habit this item breaks is treating version 3 as a synonym for encrypted: the version brings the user-based security model, and the level decides what that model actually applies. Source: Cisco 200-301 CCNA v1.1 Exam Topics - Section 4: IP Services

Answer: D. Topic 4.7, queuing. Low latency queuing adds a strict priority queue to class-based weighted fair queuing, and the priority command gives that class its bandwidth. Cisco's LLQ configuration guide describes what happens when the class is offered more: if the high priority traffic exceeds the bandwidth, and there is congestion in the network, excess traffic is dropped - the same behaviour whether the bandwidth is given in kbps or as a percentage. The discard is tied to congestion: the guide attaches it to the case in which the priority traffic exceeds its bandwidth and there is congestion in the network. The excess is not handed to class-default or re-marked by the priority command, so in this scenario the genuine voice calls sharing the VOICE class are exposed to the same drops as the mismarked video. Source: Cisco 200-301 CCNA v1.1 Exam Topics - Section 4: IP Services; excess priority traffic verified at Cisco QoS Congestion Management Configuration Guide, 'Low Latency Queueing with Priority Percentage Support' ('if the high priority traffic exceeds the bandwidth, and there is congestion in the network, excess traffic is dropped'), https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_conmgt/configuration/15-mt/qos-conmgt-15-mt-book/qos-conmgt-llq-pps.html

Answer: B. Topic 4.3 covers the role of DNS, and caching is the part of that role that decides how fast a change takes effect. RFC 1035 defines the TTL of a resource record as 'a 32 bit signed integer that specifies the time interval that the resource record may be cached before the source of the information should again be consulted.' RFC 1034, section 3.6, states: 'The meaning of the TTL field is a time limit on how long an RR can be kept in a cache.' and 'The TTL is assigned by the administrator for the zone where the data originates.' It then gives the operational advice this item turns on: 'If a change can be anticipated, the TTL can be reduced prior to the change to minimize inconsistency during the change, and then increased back to its former value following the change.' Clients and resolvers that cached the old answer with a long TTL keep using 10.1.9.40 regardless of what the server now says. Sources: https://www.rfc-editor.org/rfc/rfc1034.html and https://www.rfc-editor.org/rfc/rfc1035.html Source: IETF RFC 1034 section 3.6 ('If a change can be anticipated, the TTL can be reduced prior to the change to minimize inconsistency during the change'), https://www.rfc-editor.org/rfc/rfc1034.html; RFC 1035 section 3.2.1 (TTL definition), https://www.rfc-editor.org/rfc/rfc1035.html