Week 2: The Network Layer
Hereby, in the second week of the course, let us explore the field of network layer more closely. It will devote itself to the addresses of Internet Protocol schemes and how subnetting takes place. In addition, it includes encapsulation-how protocols such as ARP create a layer network-and the foundations of routing and routing protocols. At the end of this module, you will be able to:
Learning Objectives:
- Describe the Internet Protocol addressing scheme.
- Explain subnetting.
Binary math to describe subnets. - Demonstrate how encapsulation works.
- Understand how ARP allows different layers of the network to communicate.
- Describe how the Internet functions.
- Understand routing and routing protocols in brief.
PRACTICE QUIZ: THE NETWORK LAYER
1. Please select all of the valid IP addresses. Check all that apply.
- 123.456.123.456
- 257.70.312.49
- 192.168.1.1 (CORRECT)
- 8.8.8.8 (CORRECT)
Nice job! 8.8.8.8 is a valid IP address.
2. How many IP addresses does a class C network have?
- 256 addresses (CORRECT)
- 1 address
- 65,536 addresses
- 16,777,216 addresses
Wohoo! You’re correct.
PRACTICE QUIZ: SUBNETTING
1. What does CIDR stand for?
- Classfull Identification Routing
- Classfull Inter-Destination Routing
- Classless Inter-Domain Routing (CORRECT)
- Classless Internet Destination Routing
Yep! CIDR stands for Classless Inter-Domain Routing.
2. Which of the following is a correct form of CIDR notation?
- 192.168.1.0/24 (CORRECT)
- 192.168.1.0 + 255.255.255.0
- 192.168.1.0\24
- 192.168.1.0:24
Awesome job! CIDR (Classless Inter-Domain Routing) representation is a forward slash with bits of a subnet mask. In the case of the IP address 192.168.1.0/24, the “/24” indicates that the first 24 bits of the address are for the network portion, while the rest is for the host portion.
3. How many octets does a subnet mask have?
- 1
- 2
- 3
- 4 (CORRECT)
Great work! A subnet mask is the same length as an IP address.
PRACTICE QUIZ: ROUTING
1. Select examples of routing protocols. Check all that apply.
- User Datagram Protocol
- Transmission Control Protocol
- Border Gateway Protocol (CORRECT)
- Hypertext Transfer Protocol
- Routing Information Protocol (CORRECT)
Nice job! You’re correct.
2. Who is permitted to use non-routable address space?
- The IANA
- The IETF
- Anyone (CORRECT)
- It’s for testing purposes only
Awesome! Anyone can use non-routable address space.
3. A typical routing table may contain which of the following? Check all that apply.
- TTL
- Total hops (CORRECT)
- Destination network (CORRECT)
- Destination address
Routing table entry must also be aware of the number of hops he has to cross in reaching a destination network, so that best path for routing packets can be the determined.
You’re spot on! A routing table entry should, in some sense, be tied to a destination network: it specifies how that destination network is to be reached from the source.
GRADED QUIZ: ROUTING PATHS AND SUBNETS
1. Let’s see how much you’ve learned about routing paths and subnetting! In this activity, you are given a bunch of source and destination IP address pairs. Your task is to route each of these packets from the correct source network to the correct destination network.
Step 1: You will be presented 8 source and destination IP address pairs in the table below.
Step 2: You will mimic how the packets travel from the source IP address to the destination IP address within the network. Click the network source (the corresponding orange bubble) and click all the networks it needs to use in order to reach the destination network. You will need to click each network in the right order.
Step 3: After you’ve selected the source and destination networks, click the “Check” button. Some of these address pairs may not be represented by the networks available. If that’s the case, click the “Source or destination not present” button. If you make a mistake, click the “Reset” button to try again.
Step 4: Once you have correctly answered a question, move on to the next question by clicking on the next question arrow. There are 8 different questions.
Step 5: After you’ve completed all routing paths listed in the table, close the quiz and click the “Submit Quiz” button for a grade.
Question 1 of 8:
(CORRECT)
Question 2 of 8:
(CORRECT)
Question 3 of 8:
(CORRECT)
Question 4 of 8:
(CORRECT)
Question 5 of 8:
(CORRECT)
Question 6 of 8:
(CORRECT)
Question 7 of 8:
(CORRECT)
Question 8 of 8:
(CORRECT)
GRADED QUIZ: THE NETWORK LAYER
1. An ARP broadcast is sent to the special MAC address ________.
- FF:FF:FF:FF:FF:FF (CORRECT)
- 00:00:00:00:00:00
- 255.255.255.255
- 192.168.0.1
You got it! The local area network uses the Address Resolution Protocol broadcast to ask any devices in the network whether they belong to a certain IP address. When an ARP request is received by a device, it will send back its MAC address if it is the one belonging to that IP address.
2. A network device that knows how to forward data along to other networks is known as a ______.
- switch
- hub
- router (CORRECT)
- server
Right on! Router thereby forwarding relevant data packets to the destination device from one network to another so that devices can communicate to each other over different networks.
3. TTL stands for _______.
- Taco Tuesday Lunch
- Time To Live (CORRECT)
- Total Time Left
- Technical Telephony Layer
Yep! Actually it is – time to live that has been used for reigning in undesirable packets from an indefinite circulation in the network. It imposes a limit on the hops that a packet can take and, once exceeding the limit, the packet is discarded. This prevents a packet from endlessly waiting for delivery in case it does not reach its destination.
4. There are ____ octets in an IP address.
- 2
- 4 (CORRECT)
- 8
- 16
Great work! An octet represents eight bits, or one byte.
5. In binary, 1 +1 = _____.
- 2
- 10 (CORRECT)
- 1
- 0
Awesome! Just like decimal addition, binary addition also requires just two numerals – 0 and 1. While adding binary numbers
6. A single octet in an IP address represents what range of decimal numbers?
- 1-255
- 0-250
- 0-155
- 0-255 (CORRECT)
Great work! It is an 8-bit data set, an octet, that can represent the values of decimal numbers from 0 to 255, for it can represent up to 256 values from an 8-bit binary number (2^8). These values range from 00000000 (in decimal, 0) to 11111111 (in decimal, 255).
7. What information will you find in the 16-bit field in an IP datagram?
- The header length field
- The total length of the datagram it’s attached to (CORRECT)
- The Internet Protocol version
- The quality of service technologies
You got it! The ultimate field therefore becomes a 16-bit field called the Total Length field which indicates total length portion of the whole datagram, inclusive and header and data portion of the datagram. Such a field makes sure that the receiving device knows how big the whole datagram is so that it processes it properly.
8. What is eight bits of data called?
- Octet (CORRECT)
- Octuplet
- Octoploid
- Figure eight
You nailed it! Eight bits of data, or a single octet, can represent all decimal numbers from 0-255.
9. Which number cannot be represented by eight bits of data?
- 436 (CORRECT)
- 232
- 12
- 128
Woohoo! Eight bits of data, or a single octet, can represent all decimal numbers from 0-255. 436 is beyond this limit.
10. Which IP address is Class C?
- 132.26.144.52
- 128.42.39.72
- 192.37.48.98 (CORRECT)
- 224.24.45.69
Well done! Class C addresses begin with a first octet value of 192 through 223.
11. What protocol is used to discover the hardware address of a node with a certain IP address?
- CIDR, or Classless Inter-Domain Routing
- ARP table (CORRECT)
- SQL database
- Subnet mask
You got it! An ARP (Address Resolution Protocol) table is a list that relates the set of IP addresses of a local network with corresponding MAC addresses of devices. When devices want to communicate with another device on the same network, they check the ARP table for the MAC address that goes along with a specific IP address. If a device does not already have the appropriate entry in its ARP table, it sends out an ARP request for discovery.
12. Which octet of the subnet mask 255.255.255.0 will tell the router the corresponding host ID?
- The middle two octets
- The last octet (CORRECT)
- The first octet
- The first and last octet
Well done! A subnet mask defines the size of a subnet. For instance, with the subnet mask of 255.255.255.0, the network and subnet IDs would occupy the first three octets and represent 24 bits, while the last octet offers 8 bits for host IDs. Given this scenario, the maximum addresses a subnet can take is 256, but there are only 254 available for hosts because sometimes the 0 and 255 addresses are respectively reserved for the network address and broadcast address.
13. What is the maximum decimal number possible to represent with 16 bits?
- 65536 (CORRECT)
- 256
- 16
- 1600
Woohoo! The answer to the question is correct! For example, in consideration of a 16-bit number, the total number of possible values amounts to 2^16=65,536. Thus, this means that a 16-bit number could represent that number in 65,536 different ways-ranging from the number to 0 and 65535.
14. CIDR simplifies how routers and other network devices need to think about the parts of an IP address, but it also allows for more arbitrary network sizes. What does CIDR stand for?
- Costless Inter-Data Routing
- Classless Inter-Domain Routing (CORRECT)
- Clear Inter-Developer Relations
- Classic Intra-Demo Ratings
Great work! CIDR stands for Classless Inter-Domain Routing, and it actually adds more flexibility in efficient allocation and subnetting of IP addresses. CIDR uses a different form of addressing compared to the traditional classes, which use fixed subnet sizes like Class A, B, and C. This is done by using subnet masks in form of a slash notation, for instance, /24, referring to the number of bits that must be dedicated to the network portion of the address. By this way, the allocation of IP addresses can be made more granular for better fitting of subnetwork needs instead of wasting time addressing on IP space.
15. What type of network address space allows for nodes on a network to communicate with each other, but prevents any gateway router from forwarding traffic there, and are reserved for internal networks?
- Non-routable address space (CORRECT)
- MAC address
- IP address
- Subnet mask
Right on! It keeps communication between nodes from the same network but does not allow forwarded traffic to enter that network through gateway routers.
16. The entirety of a packet at one layer becoming the payload section at another layer is known as ________.
- subnetting
- encapsulation (CORRECT)
- fragmentation
- routing
Correct: For sure! Encapsulation operates with every layer of the network stack, except for the physical layer. At each layer, information is wrapped up in a specific header (or sometimes trailer) containing the control information that the processing functions at that layer require.
17. The process of taking a large network and splitting it up into many individual and smaller subnetworks is known as ________.
- Routing Frequency Control
- Request For Comments (CORRECT)
- Realtime Frame Check
- Redundant Frame Controller
Correct: Definitely! RFCs stand for Request for Comments and have their special importance in defining and standardizing in network and computer science protocols, procedures, and technologies. They are put forth by the IETF – Internet Engineering Task Force-and form the basis for communicating and functioning together of different systems and networks.
18. RFC stands for ______.
- Routing Frequency Control
- Request For Comments (CORRECT)
- Realtime Frame Check
- Redundant Frame Controller
Correct: Indeed, RFCs play a significant role in the development and standardization of networking protocols. It formalizes the documentation and sharing of new protocols, new ideas, and improvements to any existing standards, making sure that various systems and technologies are interoperable and consistent with each other.
19. Ranges of IP addresses that anyone can use for their internal networks are known as ______.
- Subnet Masks (INCORRECT)
- Demarcation Points
- Autonomous Systems
- Nonroutable Address Space (CORRECT)
20. In binary, 1 +1 = _____.
- 2
- 10 (CORRECT)
- 1
- 0
Correct: Awesome! Binary addition is just like decimal addition, except you only have two numerals instead of ten.
22. How many bits long is an IP address?
- 32 bits (CORRECT)
- 8 bits
- 256 bits
- 64 bits
Correct: Yup! In IPv4, an IP address is a number of 32 bits divided into four octets (8 bits each). Each of the octets is expressed in decimal form, with integer values between 0 and 255, separated by period. So, the address ‘192.168.1.1’ consists of four octets: ‘192’, ‘168’, ‘1’, and ‘1’.
23. Which number cannot be represented by eight bits of data?
- 128
- 232
- 12
- 436 (CORRECT)
Correct: Exactly! Being an octet, it is 8 bits and can represent numbers in decimal from 0 to 255 (2^8 – 1). Numbers like 436 require more than one octet to represent; that’s why IP addresses comprise four octets that can accommodate larger ranges of numbers. To be more accurate, 436 would require the use of two octets since it exceeds what can be captured by a single 8-bit number.
24. QoS services are protocols that allow routers to make decisions about which IP datagram may be more important than others. Which IP header field would QoS details be found?
- Service type field (CORRECT)
- Fragmentation offset field
- Total length field
- Identification field
Correct: Nice job! You are correct! The Quality of Service (QoS) technologies put bits in the IP header, such as the Differentiated Services Code Point (DSCP) field, so that routers could prioritize some kinds of data packets over others. This allows the networks to differentiate between various IP datagrams, guaranteeing that the most crucial types of traffic, such as voice or video, are given qualified resources for ideal performance while email or less urgent forms of data packets are considered and handled at a much lower priority. Such QoS is important for the performance of the network, especially in low bandwidth conditions or under heavy traffic loads.
25. What is the correct term for the list of IP addresses and the MAC addresses associated with them?
- File transfer protocol (FTP)
- SQL database
- ARP table (CORRECT)
- Directory service
Correct: Indubitably! ARP (Address Resolution Protocol) offers mapping of an IP address to a MAC (Media Access Control) address within a local area network. An ARP request is sent by a device that intends to send a message to another device on the same network, knowing only its IP address. The MAC address’s owner replies with the MAC address, and then, the first device transmits its information to the new address hardware.
26. What is the process of taking a large network and splitting it up into many individual and smaller subnetworks called?
- Clustering
- Cloud computing
- Subnetting (CORRECT)
- Dynamic Host Configuration Protocol (DHCP)
Correct: Subnetting is the process of splitting up a given network into smaller sub networks or subnets.
27. Computer A wants to send some data to computer B. Computer A knows that Computer B is not on its local network, so it sends the packet to the router between Network A and Network B. Based on how many network hops have happened, how much will the TTL field be decremented by?
- 1 (INCORRECT)
- 6
- 8
- 2 (CORRECT)
28. ARP stands for ______.
- Anonymous Resource Protocol
- Augmented Resolution Picture
- Address Resolution Protocol (CORRECT)
- Aggressive Resource Protection
Correct: The Address Resolution Protocol (ARP) is used to resolve the mapping of the MAC address to IP address.
29. Interior gateway protocols are used by routers in order to share information within a single ________.
- collision domain
- subnet
- autonomous system (CORRECT)
- destination network
Correct: Datacenters manage an array of networks: each of these networks are within the control domain of a single organization.
30. Using logical operators, 1 AND 0 = _____.
- True
- False (CORRECT)
- 1
- 2
Correct: Therefore, in the AND operator, the output comes as one otherwise true if and when the inputs given to it are both ‘one’ or ‘true’.
31. Calculate how many decimal numbers a 4-bit number can represent.
- 256
- 16 (CORRECT)
- 4
- 8
Correct: Right on! A bit is base two. The calculation of a 4-bit number is 2^4 = 16.
32. What protocol communicates data between routers representing the edges of autonomous systems?
- Exterior gateway (CORRECT)
- Link state
- Distance-vector
- Interior gateway
Correct: External gateway protocols are the border routers which exchange routing information among autonomous systems.
33. On a Local Area Network, or LAN, what identification do nodes use to communicate with each other internally?
- Static IP address
- Physical MAC addresses. (CORRECT)
- EIN serial
- Dynamic IP address
Correct: At a small scale, nodes in a Local Area Network (LAN) communicate with each other over their physical MAC addresses.
34. Which is a valid IP address?
- 128.42.64.78 (CORRECT)
- A8:97:4F:6D:H6:0F
- 598.36.789
- 126.396.659.100
Correct: 128.42.64.78 is correctly formed, and it should hold only numbers that fall in the range that can be represented by a single octet.
35. What is the process of taking a single IP datagram and splitting it up into several smaller datagrams called?
- NAT firewall
- Clustering
- Fragmentation (CORRECT)
- Load balancing
Correct: In essence, fragmentation nails the one, lone IP datagram into several smaller datagrams.
36. What is the purpose of an ARP response?
- To prevent a flood of UDP packets
- To improve authentication security
- To send an ACK message to the broadcasting computer
- To let a computer broadcasting an ARP message know what MAC address to put into the destination hardware address field (CORRECT)
Correct: Consequently, any node desiring to send data initiates broadcast of the ARP message to MAC broadcast address, i.e. all F’s. When network interface gets this ARP broadcast, it sends back ARP Response with MAC address of network interface.