The Five-Layer Network Model – Shuffle Q/A 1

1. Which layer constructs the Ethernet frame?

Answers

• Data link layer

• Application layer

• Physical Layer

• Transport layer

Explaination: At the Data Link Layer (Layer 2) of the OSI (Open Systems Interconnection) model, an Ethernet frame is constructed. This is the second layer of the model. This layer is in charge of encapsulating data into frames before sending them over a local area network (LAN). LAN stands for "local area network." The data payload, the source and destination MAC (Media Access Control) addresses, and various control fields used for error checking and flow management are commonly included in an Ethernet frame. In local area networks (LANs), Ethernet is one of the most prevalent data link layer protocols, and it plays an integral part in the communication of devices that are part of the same network.

2. Computer 1 on network C, with IP address of 172.16.1.57, wants to send a packet to Computer 2, with IP address of 172.16.1.133. If the TTL value was set to 64 at the beginning, what is the value of the TTL once it reaches its destination?

Answers

• 64

• 0 

• 61 

• 65

Explaination: The Time-to-Live (TTL) number included inside an IP packet is what is used to control how long the packet will remain valid and prevent it from being sent around the network endlessly. The TTL value is reduced by one with each hop, which may be a router or another device that the packet travels through. The box is considered to be invalid if its TTL value hits 0.

The initial TTL value is set to 64 on Computer 1, which has an IP address of 172.16.1.57, and it wishes to transmit a packet to Computer 2, which has an IP address of 172.16.1.133. This is the situation you have described. Since both machines are connected to the same network (172.16.1.x), it is likely that they are part of the same subnet and that there will be no routers standing in their way. As a result, the TTL value will not be decreased when the message moves from Computer 1 to Computer 2 on the same subnet as it was sent.

Because it does not pass through any routers that would cause the TTL to decrease, the TTL value should stay the same when it reaches Computer 2, which is 64. This is because it does not meet any routers.

3. Computer 1 on network B, with IP address of 192.168.1.233, wants to send a packet to Computer 2, with IP address of 172.16.1.133. Which of the following has the correct IP datagram information for the fields: Version, minimum Header Length, Source IP, and Destination IP?

Answers

• Version: 4
  Header Length: 20
  Source IP Address: 192.168.233
  Destination IP address: 172.16.1.133

• Version: 5
  Header Length: 16
  Source IP Address: 10.1.1.0/24.
  Destination IP address: 172.16.1.0/24.

• Version: 4
  Header Length: 32
  Source IP Address: 10.1.1.1
  Destination IP address:172.16.1.1

• Version: 6
  Header Length: 20
  Source IP Address: 8a:1a:2b:3c:4d:5f
  Destination IP address: 2a:2b:3c:4d:8f

Explaination: To construct an IP datagram from Computer 1 on network B (IP address: 192.168.1.233) to Computer 2 with the IP address 172.16.1.133, you need to ensure that the fields in the IP header are correctly populated. Let's go through each of them:

Version: The version field in an IP header specifies the IP version being used. For IPv4, which is the most common version, the value is 4.

• Minimum Header Length: The minimum header length is the length of the IP header in 32-bit words. For a standard IPv4 header, the minimum size is five words (20 bytes). However, if options are included, this value can be more significant.
• Source IP: This field should be set to the source IP address, 192.168.1.233 in this case.
• Destination IP: This field should be set to the destination IP address, 172.16.1.133 in this case.

Here's the correct information for the fields:

• Version: 4 (indicating IPv4)
• Minimum Header Length: 5 (for a standard IPv4 header)
• Source IP: 192.168.1.233
• Destination IP: 172.16.1.133

These values are appropriate for constructing an IPv4 datagram from Computers 1 to 2 across different networks.

4. The Cat6 cable is part of the ______ layer.

Answers

• Transport

• Application

• Physical

• Network

Explaination: The Cat6 cable is included in the Open Systems Interconnection (OSI) model's first layer, which is referred to as the Physical Layer. The Physical Layer is in charge of the data's physical transmission, which includes the medium (in this example, the Cat6 cable), the data's electrical and optical properties, and how bits are encoded and conveyed over the network. Cat6 cables are an essential part of the physical layer. They are utilized in the context of networking and cabling because they allow for the transmission of data at high rates across Ethernet networks.

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

Answers

• Destination MAC address

• Port number

• TTL value

• MAC address

Explaination: When Computer 1 queries the Address Resolution Protocol (ARP) database stored on Router Y, it looks for information on the mappings that exist on the local network between IP addresses and MAC (Media Access Control) numbers. The following is an example of the information that Computer 1 may locate in the ARP table located on Router Y:

1. IP Address: The Internet Protocol (IP) addresses of devices that are part of the local network segment to which Router Y is connected. Typically, other computers are on the same subnet as Computer 1.
2. MAC Addresses: These are the MAC addresses that correspond to the IP addresses given in the ARP table. This mapping transports Ethernet frames to the suitable nodes and devices on the local area network.
3. Interface Information: Router Y stores information about its network interfaces, including the MAC addresses associated with each interface. This information may be accessed using its administration interface. This is very necessary to route traffic between the various networks.

When Computer 1 wishes to interact with another device on the local network, it first checks its ARP table to determine whether it has the MAC address corresponding to the other device's IP address. Whether it does, Computer 1 initiates communication with the other device. Computer 1 will submit an ARP request to Router Y if the MAC address is not found in its local ARP table. The purpose of this request is to get the MAC address that is linked with the destination IP address. In response to the ARP request, Router Y looks for the MAC address information in its own ARP table so that it may provide it to the requesting device.

6. Computer 1 on network C, with IP address of 172.16.1.57, wants to send a packet to Computer 2, with IP address of 192.168.1.14. Taking in consideration that computer 1 is sending a request to a web server on computer 2, listening on port 80, and the source port on computer 1 is 5000, which of the following contains the correct information for the fourth TCP segment of data?

Answers

• 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

Explaination: To construct the correct information for the fourth TCP segment of data in this scenario, where Computer 1 (IP address: 172.16.1.57) is sending a request to a web server on Computer 2 (IP address: 192.168.1.14) listening on port 80, and Computer 1 is using source port 5000, you would typically have the following values in the TCP header:

Source Port: 5000 (the source port used by Computer 1)

Destination Port: 80 (the destination port for HTTP, which is used by the web server on Computer 2)

Sequence Number: The sequence number should reflect the initial sequence number plus the accumulated data length in the previous segments sent in this connection. The exact value depends on the previous segments' sequence numbers.

Acknowledgment Number: This should acknowledge the receipt of the previous TCP segment from Computer 2. Again, the exact value depends on the sequence numbers of the received segments.

Data Offset: The data offset (or header length) should be set to an appropriate value based on the size of the TCP header.

Flags: For a regular data segment, the ACK (acknowledgment) flag should be set to 1 to acknowledge the receipt of data. The PSH (Push) flag may be set if this segment carries data that the receiver should push up to the application layer. The URG (Urgent) flag is typically not set for a regular data segment.

Window Size: The window size indicates the amount of data that Computer 1 is willing to receive from Computer 2 before sending further acknowledgments. The value can vary depending on the congestion control and flow control.

Checksum: The checksum should be calculated based on the TCP header and data content.

Urgent Pointer: If the URG flag is not set (which is the case for a regular data segment), this field can be ignored.

Options: If any TCP options are used, they should be included as necessary.

The exact values for the Sequence Number and Acknowledgment Number depend on the specific sequence of the TCP connection and the previous segments exchanged between Computer 1 and Computer 2. You'll need to reference the sequence numbers from the previous segments in the connection to construct the correct values for the fourth TCP segment.

7. When constructing the Ethernet datagram to send the packet from Router Z to Computer 2, which is on Network C, what information needs to be in the destination MAC address?

Answers

• Computer 2’s MAC address

• Router Y’s MAC address

• Computer 1’s MAC address

• No MAC address is needed

Explaination: The MAC address of the network interface card (NIC) of Computer 2 should be used as the destination MAC address when creating an Ethernet datagram to transmit a packet from Router Z to Computer 2 on Network C. This is because the Ethernet datagram will be sent across Network C. The destination media access control (MAC) address is checked to ensure the data packet is sent to the appropriate location inside the local area network.

A standard procedure called an ARP (Address Resolution Protocol) request has to be carried out by Router Z to get the correct destination MAC address for Computer 2. The steps are as follows:

To determine the MAC address of Computer 2 given its IP address (such as 192.168.1.14), Router Z will make an ARP request to the local network, denoted by the letter C. The purpose of broadcasting this ARP request over the local network is to locate the MAC address that corresponds with the IP address of Computer 2.

Because Computer 2 is part of the same local network as Computer 1, it will provide its MAC address in response to the ARP request.

Following receipt of the ARP response, Router Z will now have the appropriate MAC address for Computer 2. When it sends the packet to Computer 2, it will use this MAC address as the destination MAC address in the Ethernet frame.

Therefore, the MAC address of Computer 2 should be used as the destination MAC address in the Ethernet datagram. This address may be determined via the process of ARP resolution. This guarantees that the data packet will be sent to Computer 2 inside Network C appropriately.

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

Answers

• Sends back the packages to router Y for confirmation

• Decrements the TTL by 1, calculates a new checksum, and makes a new IP datagram. This new IP datagram is again encapsulated on a new Ethernet frame.

• Strips away the Ethernet frame, leaving the IP datagram. Performs a checksum calculation against the entire datagram

• Calculates a checksum and compares this checksum with the one in the Ethernet frame header

Explaination: After Router Z receives the Ethernet frame containing a packet from Computer 1 on Network A and needs to route it to Computer 2 on Network C, the last step it typically performs is to:

Decapsulate the Ethernet frame and forward the IP packet to the appropriate destination.

Here's a breakdown of the process:

• Receiving the Ethernet Frame: Router Z first receives the Ethernet frame on one of its network interfaces.
• Decapsulation: It then decapsulates the Ethernet frame, extracting the IP packet from the frame. The Ethernet frame's MAC addresses determine the next-hop router or destination network.
• Routing Decision: Router Z makes a routing decision based on the destination IP address in the IP packet's header. It consults its routing table to determine the next hop or interface to which the IP packet should be forwarded.
• Forwarding the IP Packet: The router forwards the IP packet to the appropriate next hop or out of the appropriate interface. This could be another router or, in this case, the network segment (Network C) where Computer 2 is located.
• ARP Resolution: If the next hop is on a different network segment, Router Z may need to perform ARP (Address Resolution Protocol) to resolve the MAC address of the next-hop router's interface that leads to Network C.
• Forwarding to Computer 2: Once the IP packet reaches the destination network segment (Network C), it is then delivered to Computer 2 based on the IP address.

So, the last step Router Z does after receiving the Ethernet frame is to decapsulate the frame, perform any necessary routing or forwarding decisions, and send the IP packet toward its final destination, which is Computer 2 on Network C.

9. Computer 1 on network A, with IP address of 10.1.1.8, wants to send a packet to Computer 2, with IP address of 172.16.1.64. If the TTL value was set to 64 at the beginning, what is the value of the TTL once it reaches its destination?

Answers

• 65

• 60

• 0

• 62

Explaination: When Computer 1 (IP address: 10.1.1.8) transmits a packet to Computer 2 (IP address: 172.16.1.64), the packet may pass through a number of routers or other network devices on its journey from Network A to the target network. The TTL value, often known as the "Time to Live," in an IP packet will decrease by one with each successive hop. If the TTL value was initially set to 64, and the packet traveled through, say, four routers before arriving at its destination in Network 2, then the TTL value would be reduced by four (64 minus 4 = 60). Therefore, the TTL value that will be present on the destination computer (Computer 2) will be sixty. The TTL is a hop count that helps guarantee that packets do not circulate forever and prevents packets from looping indefinitely inside the network. It also helps ensure that packets do not loop indefinitely.

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

Answers

• Transport

• Physical

• Network

• Application

Explaination: The Physical Layer is in charge of transmitting ones and zeros from Computer 1 to Computer 2 using a procedure known as modulation. At this layer, the data is transformed into signals that may be transferred via physical media, such as cables or wireless communications. These signals may be electrical, optical, or radio waves. The process of representing digital data as analog signals for the purpose of transmission via a variety of different kinds of physical media is referred to as modulation. The physical conveyance of data is the responsibility of this layer, which sits at the bottom of the OSI model.

11. If it’s a TCP connection, which is the first segment that computer 1 needs to build?

Answers

• IP datagram

• handshake

• TCP segment

• Ethernet frame

Explaination: A dependable connection is created with the help of the TCP three-way handshake, which includes the TCP SYN section. Following transmitting a TCP SYN segment from Computer 1 to Computer 2, Computer 2 will send a TCP SYN-ACK (Synchronize-Acknowledgment) segment in response. Computer 1 will then transmit an ACK (Acknowledgement) segment to indicate the successful establishment of the connection. This three-way handshake guarantees that both computers are synced and prepared to trade data reliably.

12. What information is in the payload section of the TCP segments?

Answers

• The application layer data

• ART Table

• The MAC address of Computer 1

• Handshake

Explaination: The actual data that is being sent between the devices that are connecting is included inside the payload part of a TCP segment, which stands for the Transmission Control Protocol. In common parlance, the payload is often known as the "application data" or the "user data."