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Module 3 challenge: The Five-Layer Network Model: The Bits and Bytes of Computer Networking (Technical Support Fundamentals) Answers 2025

1

Computer 1 on network B (192.168.1.233) wants to send a packet to Computer 2 (10.1.1.205). On which network is Computer 2?

A. Not present
B. Network C
C. Network B
D. Network A ✅

Explanation: 10.1.1.205 falls in 10.1.1.0/24 → Network A.

2

What information is computer 1 looking at in the ARP table on Router Y?

A. MAC address ✅
B. Port number
C. Destination MAC address
D. TTL value

Explanation: ARP maps IP → MAC address. The ARP table contains MAC addresses for given IPs so the router can build layer-2 frames.

3

Which layer constructs the IP datagram?

A. Physical Layer
B. Application layer
C. Network layer ✅
D. Data layer

Explanation: The Network layer (Layer 3) creates IP datagrams (adds IP header around transport payload).

4

What information is in the data payload of the Ethernet frame?

A. Handshake
B. ART message
C. IP datagram ✅
D. network interface

Explanation: An Ethernet frame’s payload carries the IP datagram (or other network-layer packet types).

5

When Router Z constructs the Ethernet datagram to send the packet to Computer 2 (on Network C), what must be in the destination MAC address?

A. Computer 2’s MAC address ✅
B. No MAC address is needed
C. Computer 1’s MAC address
D. Router Y’s MAC address

Explanation: On the local link to Computer 2, the frame’s destination MAC is the MAC of Computer 2.

6

Computer 1 on Network A sends a packet to Computer 2 on Network C. What’s the first step Router Z does after receiving the Ethernet frame?

A. Sends an ARP broadcast message
B. Increases the TTL by one
C. Checks the destination IP address and changes it to its own
D. Calculates a checksum and compares this checksum with the one in the Ethernet frame header ✅

Explanation: Upon receipt the router (or NIC) first validates the frame (FCS/checksum) to verify integrity before handing the payload up to IP processing. (After validation, router inspects destination IP to route/forward and decrements TTL.)

7

Computer 1 on Network C (172.16.1.57) -> Computer 2 (172.16.1.133). If TTL was 64 at start, what is TTL when it reaches destination?

A. 64 ✅
B. 65
C. 61
D. 0

Explanation: Both hosts are on the same network (no routers traversed), so TTL is unchanged → remains 64.

8

Computer 1 on Network C (src port 5000) → Computer 2 (web server, dst port 80). Which option contains correct info for the fourth TCP segment of data?

  • Source Port: 5000
    Destination Port: 80
    Sequence Number: 1
    Acknowledgment Number: 2

  • Source Port: 8081
    Destination Port: 50
    Sequence Number: 4
    Acknowledgment Number: 1

  • Source Port: 5000 ✅
    Destination Port: 80 ✅
    Sequence Number: 4 ✅
    Acknowledgment Number: 5 ✅

  • Source Port: 80
    Destination Port: 5000
    Sequence Number: 1
    Acknowledgment Number: 1

Explanation: The only option with correct source/destination ports (5000 → 80) and sequence/ack values consistent with “fourth segment” (sequence/ack numbers incrementing per segment in this simplified example) is the third option.

9

Computer 1 on network B (192.168.1.121) → Computer 2 (172.16.1.57). Which IP datagram fields are correct: Version, minimum Header Length, Source IP, Destination IP?

A. Version: 4 ✅
Header Length: 20 ✅
Source IP Address: 192.168.1.121 ✅
Destination IP address: 172.16.1.57 ✅

B. Version: 6 … (wrong format)
C. Version: 5 … (invalid)
D. Version: 4 Header Length: 32 … (header length incorrect, and addresses wrong)

Explanation: IPv4 uses Version = 4 and a minimum header length of 20 bytes. Source/destination IPs match the question.

10

The ________ layer is responsible for sending ones and zeros through a process called modulation from Computer 1 to Computer 2.

A. Network
B. Transport
C. Physical ✅
D. Application

Explanation: The Physical layer handles the transmission of raw bits (ones and zeros) and modulation onto the medium.

Summary

  • Computer 2 (10.1.1.205) → Network A.

  • ARP tables map IP → MAC address.

  • Network layer constructs IP datagrams; Ethernet frames carry IP datagrams as payload.

  • When sending on a local link, destination MAC = destination host’s MAC.

  • Router first validates frame (checksum/FCS) then processes IP (routing, TTL decrement).

  • Same-subnet traffic does not pass routers (TTL unchanged).

  • TCP segments include source/dest ports and sequence/ack numbers; the listed segment with src=5000 dst=80 seq=4 ack=5 is the fourth-segment example.

  • IPv4 datagram: Version 4, header length 20 bytes (min).

  • Physical layer handles modulation of bits.