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Network+ (N10-009). Set it up and run it.
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Study mode marks each answer and tells you why the right one is right and why each
wrong one is wrong; Simulation puts a clock on it and chooses each question from
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The five questions
1. Refer to the exhibit. A technician runs a command on a workstation that cannot reach any other subnet. What is the most likely cause?
- A. The address is in the APIPA range and no DHCP server responded
- B. The default gateway is not inside the host's own subnet
- C. The DNS suffix does not match the domain the host belongs to
- D. The subnet mask is too small for the number of hosts on the segment
Correct answer: B.
With a 255.255.255.0 mask the host's subnet is 192.168.20.0 through 192.168.20.255. The gateway 192.168.21.1 is outside that range, so the host has no way to reach it and cannot forward anything off the local subnet.
Why the others are wrong. The mask is a normal /24 and nothing in the output suggests it is too small. The DNS suffix affects name resolution, not whether packets leave the subnet. The address is in RFC 1918 space, not the 169.254 APIPA range, so DHCP is not implicated by the output.
2. A technician maps the four-layer TCP/IP model onto the seven-layer OSI model. Which two OSI layers are combined into the TCP/IP link layer? (Choose two.)
- A. Network
- B. Transport
- C. Physical
- D. Data link
- E. Session
Correct answer: C.
The TCP/IP model's link layer, sometimes called network access, covers everything needed to put a frame on a specific medium. That is the OSI physical and data link layers taken together, which is why TCP/IP has four layers where OSI has seven.
Why the others are wrong. The network layer maps to the TCP/IP internet layer on its own and is not folded in with the link layer. The transport layer maps directly to the TCP/IP transport layer with the same name. The session layer is one of the three OSI layers that TCP/IP rolls into a single application layer, along with presentation and application.
3. A technician captures traffic and sees a frame carrying a source and destination MAC address but no IP header. At which OSI layer is this frame handled?
- A. Layer 4, because the frame is part of an end-to-end conversation
- B. Layer 1, because MAC addresses are burned into the physical interface
- C. Layer 3, because addressing of any kind is a network layer function
- D. Layer 2, because MAC addressing and framing belong to the data link layer
Correct answer: D.
MAC addressing, framing, and error detection on a single link are data link layer functions, which is layer 2. A frame that carries no IP header has nothing above the data link layer to process, so layer 2 is where it is handled.
Why the others are wrong. Layer 1 is the physical layer and deals with voltages, light and bit timing rather than addresses; the fact that a MAC address is stored on the interface does not move addressing down a layer. Layer 3 addressing is IP addressing, and this frame has no IP header at all. Layer 4 handles end-to-end segmentation with TCP or UDP, which sits above the missing layer 3 header.
4. An application sends a message that is broken into segments, each stamped with a source and destination port number. Which OSI layer performs this work?
- A. The network layer, because ports are how routers separate flows
- B. The transport layer, because segmentation and port addressing happen there
- C. The session layer, because ports identify a conversation between hosts
- D. The presentation layer, because ports select the format the receiver expects
Correct answer: B.
Layer 4, the transport layer, divides application data into segments and adds the source and destination port numbers that identify which process on each host the data belongs to. TCP and UDP are both transport layer protocols.
Why the others are wrong. The session layer establishes and tears down dialogues but does not assign ports. The presentation layer handles formatting, encoding and encryption, not addressing. The network layer moves packets between networks using IP addresses; routers make forwarding decisions on IP, and a device that looks at ports is doing more than a layer 3 job.
5. A technician needs to name the layer where TLS encryption and character encoding are normally placed in the OSI model. Which layer is it?
- A. Layer 4, the transport layer
- B. Layer 6, the presentation layer
- C. Layer 5, the session layer
- D. Layer 7, the application layer
Correct answer: B.
The presentation layer is where data is translated into a form the receiving application can use, which the OSI model defines as encoding, compression and encryption. TLS is placed at layer 6 in OSI terms even though it runs directly over TCP in a real stack.
Why the others are wrong. The session layer manages the dialogue itself, opening, maintaining and closing it, rather than transforming the data. The application layer is the interface the user's program talks to and sits above the translation step. The transport layer provides the reliable stream TLS runs on but does no encoding or encryption of its own.
6. A router receives a packet, strips the frame, reads the destination IP, and builds a new frame for the next hop. Which layers has the router processed?
- A. Layers 3 through 7
- B. Layer 3 only
- C. Layers 1 through 4
- D. Layers 1 through 3
Correct answer: D.
To do this the router must receive bits on the wire, which is layer 1, de-encapsulate the frame, which is layer 2, and read the destination IP address to make a forwarding decision, which is layer 3. It then rebuilds layers 2 and 1 for the outgoing link.
Why the others are wrong. Layer 4 is not involved because the router does not read port numbers to forward a normal packet; a device that does so is doing more than routing. Layers 3 through 7 skips the physical and data link work every device must do to receive the packet at all. Layer 3 alone ignores the framing and the physical reception that had to happen first.
7. Users can reach a web server by IP address but not by name. Using the OSI model to structure the investigation, which layer should the technician suspect first?
- A. Layer 3, because routing to the server is clearly failing
- B. Layer 7, because name resolution is an application layer service
- C. Layer 2, because the switch is not forwarding the frames
- D. Layer 4, because the TCP session is not being established
Correct answer: B.
Reaching the server by IP proves that layers 1 through 4 are working end to end. DNS is an application layer service, so a failure that only affects names points at layer 7 and specifically at name resolution.
Why the others are wrong. A layer 3 routing failure would break the connection by IP address as well, and it does not. A layer 2 switching failure would stop the frames reaching the default gateway at all. A layer 4 failure would prevent the TCP handshake, which is clearly completing because the site loads by address.
8. A technician describes the process of adding a header at each layer as data moves down the sending host's stack. What is this process called?
- A. Fragmentation
- B. Encapsulation
- C. Multiplexing
- D. Convergence
Correct answer: B.
Encapsulation is the process of wrapping data from the layer above in a header, and sometimes a trailer, that the peer layer on the receiving host will read. The reverse process on the receiving side is de-encapsulation.
Why the others are wrong. Fragmentation splits a single packet into smaller pieces because a link cannot carry it whole, which is a specific layer 3 action rather than the general process. Multiplexing is combining several conversations onto one channel. Convergence is the state a routing protocol reaches when every router agrees on the topology.
