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Topic: TCP & UDPSwitch
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1.0 Network Infrastructure and Connectivity

TCP & UDP Practice Questions

Transport-layer ports, reliability, sequencing, flow control, and UDP tradeoffs.

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One solved question, so you can see how these are marked

What Layer 4 feature lets one host keep separate web and SSH conversations open at the same time?

Port numbers multiplex separate transport conversations

Transport-layer source and destination port numbers identify the application conversations, allowing many sessions to share the same IP address.

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All 15 TCP & UDP questions in this set

Answers and explanations appear when you work through the set above.

  1. A client opens an outbound TCP connection from source port 53124. Which IANA port range does that source port belong to?

    • Well-known
    • Registered
    • Dynamic/private (ephemeral)
    • Reserved network-device interface ports

  2. Which TCP behavior provides reliable delivery when a transmitted segment does not arrive?

    • Retransmits unacknowledged data after loss detection
    • The receiver's advertised window repairs the missing data
    • The sender's checksum recreates the missing segment
    • The connection handshake reserves bandwidth to prevent loss

  3. Packets from a file transfer arrive out of order. Which TCP mechanism lets the receiver reassemble the original byte stream?

    • TCP sequence numbers
    • Port security
    • Default gateway IP
    • TTL

  4. Which TCP field participates in flow control by telling a sender how much data a receiver can accept?

    • Window size
    • DSCP (differentiated services code point)
    • Hop limit
    • VLAN ID

  5. Which statement accurately describes UDP at the transport layer?

    • Establishes an acknowledged transport connection before data
    • Retransmits lost datagrams after receiving a negative acknowledgment
    • Checksum detection without sequencing or flow control
    • Uses well-known ports for the source and destination of every datagram

  6. Why is UDP often chosen for real-time voice or video?

    • Ordered delivery by buffering media until missing packets arrive
    • Low overhead without connection setup or transport retransmissions
    • It encrypts media by default
    • It prevents packet loss on congested links

  7. A network engineer says a TCP session is identified only by the destination port. What important information is missing?

    • Source and destination IP addresses and ports
    • The switchport speed and duplex at each endpoint of the connection
    • The router's OSPF process ID
    • The frame's preamble

  8. Which range contains IANA well-known port numbers?

    • 0-1023
    • 1024-49151
    • 49152-65535
    • 65536-131071

  9. Which protocol is connection-oriented at the transport layer?

    • TCP
    • UDP (User Datagram Protocol)
    • IP
    • ARP

  10. In a normal TCP connection establishment with no data in the handshake, which flag sequence appears first?

    • ACK, FIN, ACK
    • SYN, SYN-ACK, ACK
    • SYN, RST, FIN
    • FIN, FIN-ACK, SYN

  11. A TCP client sends SYN with sequence number 7000 and no payload. Which acknowledgment number should the server use in its SYN-ACK?

    • 6999
    • 7000
    • 7001
    • 8000

  12. A TCP receiver has all bytes through 2499 in order, with no SYN or FIN involved in this exchange. Which cumulative acknowledgment number does it send?

    • 2500
    • 2499
    • 2498
    • 1

  13. An established TCP peer advertises a receive window of zero. What does this tell the sender?

    • The destination port is closed
    • Every transmitted byte has been lost
    • The connection must immediately be reset
    • The receiver cannot accept more data for now

  14. Which TCP flag lets a sender indicate an orderly end to its own byte stream?

    • RST
    • FIN
    • SYN
    • URG

  15. A TCP server listens on port 443. Which port pair would normally appear in its reply to a client using source port 53000?

    • Source 53000, destination 443
    • Source 443, destination 443
    • Source 443, destination 53000
    • Source 53000, destination 53000