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Objective 1.5

200-301

Compare TCP to UDP.

Objective 1.5 sits in Network Fundamentals, which carries 20% of the CCNA exam. The questions below are original, written from the official objective title above, and each explanation cites the Cisco page it rests on.

Objective title verbatim from the official objectives. Cisco exam page ↗

A worked example

Shown solved, with the whole explanation open: this is what every question here carries.

1-5Network Fundamentals

An inventory application sends readings over UDP across a flapping WAN link, and the database occasionally records the same reading twice. Which transport behavior explains it?

UDP delivers datagrams to the application in sequence orderOrdering is exactly what RFC 768 sends an application to TCP for. Datagrams are handed up as they arrive.
UDP retransmits any datagram the receiver fails to acknowledgeRetransmission on a missing acknowledgement is a TCP mechanism. There is no acknowledgement field to trigger it here.
UDP does not guarantee protection against duplicate datagramsCorrect · your answerCorrect. Duplicate suppression is absent, so a repeated datagram reaches the application.
UDP opens a connection before the first datagram is sentNo handshake precedes a UDP datagram, which is why a first payload can be sent with zero round trips.

Correct.

Checked against datatracker.ietf.org, August 2026

Concept

A transport that keeps no per-message state cannot tell a fresh message from a copy of one it has already handed up. Anything that has to notice a repeat, a loss or an out-of-order arrival must be built into the application sitting above it.

Why C

RFC 768 states the protocol is transaction oriented and that delivery and duplicate protection are not guaranteed, and it points applications needing ordered reliable streams at TCP instead. A datagram copied by a retransmitting link or a multipath route therefore reaches the application twice, and nothing in the transport strips the copy.

Source

This protocol provides a procedure for application programs to send messages to other programs with a minimum of protocol mechanism. The protocol is transaction oriented, and delivery and duplicate protection are not guaranteed.

IETF RFC 768: User Datagram Protocol, checked August 2026
#udp#reliability#transport-choice

Now you: objective 1.5 questions

No account needed. The explanation opens when you answer.

Sample question 1 of 3

1-5Network Fundamentals

A capture taken during a slow file download shows the client's acknowledgements to the server.

14:02:11.418 IP 10.1.20.55.51422 > 10.1.30.8.443: Flags [.], ack 84921, win 64240, length 014:02:11.905 IP 10.1.20.55.51422 > 10.1.30.8.443: Flags [.], ack 148329, win 17520, length 014:02:12.376 IP 10.1.20.55.51422 > 10.1.30.8.443: Flags [.], ack 201440, win 0, length 0

What does the falling win value report?

Sample question 2 of 3

1-5Network FundamentalsChoose 2

An engineer moves a nightly file transfer onto a lossy WAN link where segments are dropped. Which two TCP mechanisms recover the missing data? (Choose two.)

Sample question 3 of 3

1-5Network Fundamentals

An application sends short messages and tolerates the occasional loss or duplicate. Which transport property of UDP makes it a fit?

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Read the sources

These are the official pages the questions above cite. Reading them is studying the objective from the primary source, which is what the explanations point you toward anyway.

More objectives in Network Fundamentals