Ip4 Addressing And Osi Model

Front 1

What is a network?

Back 1

A network is a collection of devices and end systems.
Networks consist of computers, servers, and network devices, such as switches and routers, that can communicate with each other.

Front 2

What are the four major categories of physical components of a computer network?

Back 2

- Personal computers (PCs): Send and receive data and are the endpoints of the network.
- Interconnections: The components that provide a means for data to travel across the network. This includes network interface cards (NIC), network media, and connectors.
- Switches: Provide network access for the PCs.
- Routers: Interconnect networks.

Front 3

What is the difference between the physical and logical network topology?

Back 3

Physical topology defines the physical components of the network: cables, network devices, and computers.
Logical topology defines the data path of the network.

Front 4

What are six reasons the OSI reference model was created?

Back 4

Six reasons that the OSI reference model was created are as follows:
- To ensure that different vendors' products can work together
- To create standards to enable ease of interoperability by defining standards for the operations at each level
- To clarify general functions of internetworking
- To divide the complexity of networking into smaller, more manageable sublayers
- To simplify troubleshooting
- To enable developers to modify or improve components at one layer without having to rewrite an entire protocol stack

Front 5

What are the seven layers of the OSI reference model? Include the layer number and name of each layer in your answer.

Back 5

The seven layers of the OSI reference model are as follows:
- Layer 7: Application layer
- Layer 6: Presentation layer
- Layer 5: Session layer
- Layer 4: Transport layer
- Layer 3: Network layer
- Layer 2: Data link layer
- Layer 1: Physical layer

Front 6

What is the function of the OSI model's physical layer (Layer 1)? Give some examples of physical layer implementations.

Back 6

The physical layer defines the physical medium. It defines the media type, the connector type, and the signaling type (baseband versus broadband). This includes voltage levels, physical data rates, and maximum cable lengths. The physical layer is responsible for converting frames into electronic bits of data, which are then sent or received across the physical medium. Twisted-pair, coaxial, and fiber-optic cable operate at this level. Other implementations at this layer are repeaters/hubs.

Front 7

What is the responsibility of the data link layer (Layer 2)?

Back 7

The data link layer defines how data is formatted from transmission and how access to the physical media is controlled. This layer also typically includes error correction to ensure reliable delivery of data.
The data link layer translates messages from the network layer into bits for the physical layer, and it enables the network layer to control the interconnection of data circuits within the physical layer. Its specifications define different network and protocol characteristics, including physical addressing, error notification, network topology, and sequencing of frames.
Data-link protocols provide the delivery across individual links and are concerned with the different media types, such as 802.2 and 802.3. The data link layer is responsible for putting 1s and 0s into a logical group. These 1s and 0s are then put on the physical wire. Some examples of data link layer implementations are IEEE 802.2/802.3, IEEE 802.5/802.2, packet trailer (for Ethernet, frame check sequence [FCS], or cyclic redundancy check [CRC]), Fiber Distributed Data Interface (FDDI), High-Level Data Link Control (HDLC), and Frame Relay.

Front 8

The Institute of Electrical and Electronics Engineers (IEEE) defines what two sublayers of the data link layer?

Back 8

The IEEE defines the following two sublayers of the data link layer:
- The Logical Link Control (LLC) sublayer
- The Media Access Control (MAC) sublayer
These two sublayers provide physical media independence.

Front 9

For what is the Logical Link Control (LLC) sublayer responsible?

Back 9

The Logical Link Control (802.2) sublayer is responsible for identifying different network layer protocols and then encapsulating them to be transferred across the network.
Two types of LLC frames exist: Service access point (SAP) and Subnetwork Access Protocol (SNAP). An LLC header tells the data link layer what to do with a packet after it is received.

Front 10

What functions does the Media Access Control (MAC) sublayer provide?

Back 10

The MAC sublayer specifies how data is placed and transported over the physical wire. It controls access to the physical medium.
The LLC sublayer communicates with the network layer, but the MAC sublayer communicates downward directly to the physical layer. Physical addressing (MAC addresses), network topologies, error notification, and delivery of frames are defined at the MAC sublayer.

Front 11

What are some network devices that operate at the data link layer?

Back 11

Bridges and switches operate at the data link layer.
Both devices make decisions about what traffic to forward or drop (filter) by MAC addresses, and logical network address are not used at this layer. Data link layer devices assume a flat address space.

Front 12

Describe the function of the network layer (Layer 3). Give some examples of network layer implementations.

Back 12

The network layer provides internetwork routing and logical network addresses. It defines how to transport traffic between devices that are not locally attached.
The network layer also supports connection-oriented and connectionless service from higher-layer protocols.
Routers operate at the network layer. IP, Internetwork Packet Exchange (IPX), AppleTalk, and Datagram Delivery Protocol (DDP) are examples of network layer implementations.

Front 13

Are network layer addresses physical or logical?

Back 13

Network layer addresses are logical.
These addresses are logical addresses that are specific to the network layer protocol being run on the network. Each network layer protocol has a different addressing scheme. They are usually hierarchical and define networks first and then hosts or devices on that network. An example of a network address is an IP address, which is a 32-bit address often expressed in decimal format. An example of an IP address in decimal format is 192.168.0.1.

Front 14

What is the transport layer (Layer 4) responsible for? Give some examples of transport layer implementations.

Back 14

The transport layer segments and reassembles data from upper-layer applications into data streams. It provides reliable data transmission to upper layers.
End-to-end communications, flow control, multiplexing, error detection and correction, and virtual circuit management are typical transport layer functions. Some examples include TCP, User Datagram Protocol (UDP), and Sequenced Packet Exchange (SPX).

Front 15

What is flow control, and what are the three methods of implementing it?

Back 15

Flow control is the method of controlling the rate at which a computer sends data, thus preventing network congestion.
The three methods of implementing flow control are as follows:
- Buffering
- Source-quench messages (congestion avoidance)
- Windowing

Front 16

What are the functions of the session layer (Layer 5)? Give some examples.

Back 16

The session layer is responsible for creating, managing, and ending communication sessions between presentation layer entities.
These sessions consist of service requests and responses that develop between applications located on different network devices. Some examples include Structured Query Language (SQL), remote-procedure call (RPC), X Window System, Zone Information Protocol (ZIP), NetBIOS names, and AppleTalk ASP.

Front 17

In the OSI model, what are the responsibilities of the presentation layer (Layer 6)? Give some examples of this layer.

Back 17

Also known as the translator, the presentation layer provides coding and conversion functions to application layer data. This guarantees that the application layer on one system can read data transferred from the application layer of a different system. Some examples of the presentation layer are as follows:
- Compression, decompression, and encryption
- JPEG, TIFF, GIF, PICT, QuickTime, MPEG, EBCDIC, and ASCII file types

Front 18

What does the application layer (Layer 7) of the OSI model do, and what are some examples of this layer?

Back 18

The application layer is the layer that is closest to the user. This means that this layer interacts directly with the software application. The application layer's main function is to identify and establish communication partners, determine resource availability, and synchronize communication. Some examples include the following:
- TCP/IP applications such as Telnet, FTP, Simple Mail Transfer Protocol (SMTP), and HTTP
- OSI applications such as Virtual Terminal Protocol; File Transfer, Access, and Management (FTAM); and Common Management Information Protocol (CMIP)

Front 19

How do the different layers of the OSI model communicate with each other?

Back 19

Each layer of the OSI model can communicate only with the layer above it, below it, and parallel to it (a peer layer).
For example, the presentation layer can communicate with only the application layer, session layer, and presentation layer on the machine it is communicating with. These layers communicate with each other using service access points (SAP) and protocol data units (PDU). The SAP is a conceptual location at which one OSI layer can request the services of another OSI layer. PDUs control information that is added to the user data at each layer of the model. This information resides in fields called headers (the front of the data field) and trailers (the end of the data field).

Front 20

What is data encapsulation?

Back 20

Encapsulation wraps data with the necessary protocol information before network transmission.
A PDU can include different information as it goes up or down the OSI model. It is given a different name according to the information it is carrying (the layer where it is located). When the transport layer receives upper-layer data, it adds a TCP header to the data; this is called a segment. The segment is then passed to the network layer, and an IP header is added; thus, the data becomes a packet. The packet is passed to the data link layer, thus becoming a frame. This frame is then converted into bits and is passed across the network medium. This is data encapsulation. For the ICND test, you should know the following:
- Application layer: Data
- Transport layer: Segment
- Network layer: Packet
- Data link layer: Frame
- Physical layer: Bits

Front 21

What are the four layers of the TCP/IP stack?

Back 21

The four layers of the TCP/IP stack are as follows:
- Application
- Transport
- Internet
- Network Access

Front 22

On what layer are physical data rates, connectors, and MAC addresses located in the TCP/IP stack?

Back 22

Physical data rates, connectors, and MAC addresses are located on the network access layer.

Front 23

What are some protocols that operate at the TCP/IP Internet layer?

Back 23

Some protocols that operate at the TCP/IP Internet layer are as follows:
- IP
- ICMP (Internet Control Message Protocol)
- ARP (Address Resolution Protocol)
- RARP (Reverse Address Resolution Protocol)

Front 24

What is the Internet Protocol (IP)?

Back 24

IP is a connectionless protocol that provides best-effort delivery routing of packets.
IP has the following characteristics:
- Operates at Layer 3 of the Open Systems Interconnection (OSI) (network) and TCP/IP (Internet) model
- Is connectionless
- Uses hierarchical addressing
- Provides best-effort delivery of packets
- Has no built-in data recovery

Front 25

How many bits are in an IPv4 address? In an IPv6 address?

Back 25

IPv4: 32 bits
IPv6: 128 bits

Front 26

An IP address is a hierarchical address that consists of what two parts?

Back 26

An IP address is a hierarchical address that consists of the following two parts:
- Network ID: Describes the network to which the IP address or device belongs
- Host ID: The ID that identifies a specific host

Front 27

What are the different classes of IP addressing and the address ranges of each class?

Back 27

The different classes of IP addressing and their ranges are as follows:
- Class A: 1.0.0.0 to 126.255.255.255
- Class B: 128.0.0.0 to 191.255.255.255
- Class C: 192.0.0.0 to 223.255.255.255
- Class D: 224.0.0.0 to 239.255.255.255 (Multicasting)
- Class E: 240.0.0.0 to 255.255.255.254 (Reserved)

Front 28

What is the range of addresses for Class A networks?

Back 28

- Class A: 1.0.0.0 to 126.255.255.255

Front 29

What is the range of addresses for Class B networks?

Back 29

- Class B: 128.0.0.0 to 191.255.255.255

Front 30

What is the range of addresses for Class C networks?

Back 30

- Class C: 192.0.0.0 to 223.255.255.255

Front 31

What is the range of addresses for Class D networks?

Back 31

- Class D: 224.0.0.0 to 239.255.255.255 (Multicasting)

Front 32

What is the range of addresses for Class E networks?

Back 32

- Class E: 240.0.0.0 to 255.255.255.254 (Reserved)

Front 33

What does RFC 1918 define?

Back 33

RFC 1918 defines reserved (private) networks and addresses that are not routed on the Internet.
These addresses are as follows:
- 10.0.0.0 to 10.255.255.255
- 172.16.0.0 to 172.31.255.255
- 192.168.0.0 to 192.168.255.255

Front 34

What is the range of addresses for Class A private networks?

Back 34

- 10.0.0.0 to 10.255.255.255

Front 35

What is the range of addresses for Class B private networks?

Back 35

- 172.16.0.0 to 172.31.255.255

Front 36

What is the range of addresses for Class C private networks?

Back 36

- 192.168.0.0 to 192.168.255.255

Front 37

If an IP wants to communicate with all devices on the local network, what is the destination IP address of its broadcast?

Back 37

255.255.255.255.
This address is also called the local broadcast address.

Front 38

What is special about IP address 127.0.0.1?

Back 38

127.0.0.1 is the loopback address.
The loopback address lets the host send a message to itself to see whether TCP/IP was properly bounded to the network card.

Front 39

In a Class A network, how many octets are used for host addresses?

Back 39

3. One octet consists of 8 bits; thus a Class A network reserves 24 bits for host addresses. The maximum number of hosts a Class A network can have is 16,777,214 (2^24 - 2).

Front 40

How many hosts are available for use in a Class B network?

Back 40

65,534. A Class B network reserves 16 bits for host addresses; thus 2^16 - 2 = 65,534.

Front 41

How many hosts are available for use in a Class C network?

Back 41

254. A Class C network reserves 8 bits for host addresses. Thus 2^8 - 2 = 254.

Front 42

What is DHCP?

Back 42

Dynamic Host Configuration Protocol (DHCP) allows a host to obtain an IP address automatically and to set TCP/IP stack configuration parameters such as subnet mask, default gateway, and DNS addresses.

Front 43

What is DNS?

Back 43

The Domain Name System (DNS) converts names into IP addresses.
Instead of having to remember a host's IP address, DNS allows you to use a friendly name to access the host. For example, it is easier to remember http://www.cisco.com than 198.133.219.25.

Front 44

What two protocols function at the transport layer of the TCP/IP model?

Back 44

Two protocols that function at the transport layer of the TCP/IP model are as follows:
- TCP (Transmission Control Protocol): A connection-oriented, reliable protocol
- UDP (User Datagram Protocol): A connectionless and unacknowledged protocol

Front 45

Which has more overhead, UDP or TCP?

Back 45

TCP. Because UDP segments are not acknowledged, they do not carry the overhead that TCP does, thus allowing faster transmissions and greater efficiency.

Front 46

What are the protocol numbers for TCP and UDP?

Back 46

TCP: 6
UDP: 17

Front 47

What is reliable versus best-effort delivery?

Back 47

Reliable delivery is connection oriented, and best-effort is connectionless.

Front 48

What are TCP and UDP port numbers?

Back 48

To pass information (such as e-mail) to upper layers, TCP and UDP use port numbers. These port numbers are predefined and keep track of different conversations among different hosts at the same time. Originating source port numbers are dynamically assigned by the source host using a number in the range of 49,152 to 65,535.

Front 49

What are well-known port numbers?

Back 49

Well-known port numbers are used for fundamental applications on the Internet such as e-mail and DNS. They have a range from 1 to 1023.

Front 50

What is the port number for SMTP?

Back 50

25

Front 51

What is the port number for DNS?

Back 51

53

Front 52

What are the port numbers for FTP?

Back 52

20 and 21.
FTP uses port 20 for data transfer; port 21 is the command port

Front 53

What is the port number for TFTP?

Back 53

69

Front 54

What is the port number for Telnet?

Back 54

23

Front 55

What is a socket?

Back 55

A socket is an IP address combined with a TCP or UDP port number.
When a host wants to talk to another host, it sends its IP address along with the application (port number) it wants to communicate with. For example, if host 192.168.0.3 wants to talk to host 192.168.0.2 by e-mail, host 192.168.0.3 sends its IP address and destination port number (192.168.0.3:1023) to host 192.168.0.2 with the port number it wants to communicate with (192.168.0.2:25).

Front 56

What are the three mechanisms TCP uses to accomplish a connection-oriented connection?

Back 56

The three mechanisms TCP uses to accomplish a connection-oriented connection are as follows:
- Packet sequencing
- Acknowledgments, checksums, and timers
- Windowing

Front 57

What are the steps for the TCP three-way handshake?

Back 57

The steps for the TCP three-way handshake are as follows:Step 1. The source host sends a SYN to the destination host.
Step 2. The destination host replies to the source with an ACK. At the same time, it sends a SYN to the source host.
Step 3. The source host replies with an ACK.

Front 58

What is the purpose of flow control?

Back 58

Flow control provides a mechanism for the receiver to control the transmission speed.
TCP implements flow control by using the SYN and ACK fields in the TCP header, along with the Window field. The Window field is a number that implies the maximum number of unacknowledged bytes allowed outstanding at any time.

Front 59

What is a TCP window?

Back 59

What is a TCP window?

Front 60

What is the purpose of a three-way handshake?

Back 60

The three-way handshake initiates communication by establishing an initial sequence number and window size.

Front 61

What is the purpose of TCP sequencing?

Back 61

The purpose of sequencing is to provide reliability by requiring the recipient to acknowledge receipt of a group of segments before a timer expires.

Front 62

What fields are included in the TCP header?

Back 62

The fields included in the TCP header are as follows:
- Acknowledgment Number
- Sequence Number
- Source/Destination Port
- Window Size
- TCP Checksum

Front 63

What is an example of a Layer 2 address?

Back 63

MAC address.
MAC addresses are assigned to end devices and are used for communication over the local network. MAC addresses are hard-coded into the network card.

Front 64

What is the Address Resolution Protocol (ARP)?

Back 64

ARP is used to resolve a known IP address to a MAC address. For a host to communicate with another host, it must know the MAC address of the destination host (if they are on the same network) or next-hop router. This is the reason for ARP.

Front 65

What is the ARP table?

Back 65

The ARP table stores the reference of each known IP address to its MAC address.
The ARP table is created and maintained dynamically.

Front 66

What is the purpose of the default gateway?

Back 66

What is the purpose of the default gateway?

Front 67

A host computer has been correctly configured with a static IP address, but the default gateway is incorrect. Which layer of the OSI model is first affected by this misconfiguration?

Back 67

Layer 3.
The default gateway sends IP packets to a remote network and functions at Layer 3 of the OSI model.

Front 68

What three configuration settings does a host on a TCP/IP network require to communicate with hosts on a remote TCP/IP network?

Back 68

The configuration settings are as follows:
- IP address
- Subnet mask
- Default gateway address

Front 69

You want to test TCP/IP connectivity between two hosts. What IP tool can you use to do this?

Back 69

Ping. Ping is a tool that is part of IP that sends Internet Control Message Protocol (ICMP) packets to test network layer connectivity between two hosts. Ping sends an "echo request" packet to the target host and listens for an ICMP "echo response."

Front 70

What two utilities test IP connectivity?

Back 70

Ping and traceroute (tracert).
Ping and traceroute are ICMP utilities. ICMP can test only Layer 3 connectivity.

Front 71

List four functions of ICMP.

Back 71

Four functions of ICMP are as follows:
- Flow control
- Detect unreachable destinations
- Redirect routes
- Check remote hosts

Front 72

While troubleshooting a computer with network connectivity problems, you notice steady link lights on both the computer and the switch port the computer is connected to. However, when you issue the ping command from the computer, you receive a "Request timed out" message. On what layer of the OSI model does the problem most likely exist?

Back 72

The network layer.
Because the link lights on the computer network interface card (NIC) and workstation port are on, the physical connection is working properly. Because you are getting a "Request timed out" message, the problem most likely resides at the network layer.

Front 73

What are LAN standards?

Back 73

LAN standards define the physical media and connectors used to connect to the media at the physical layer and the way devices communicate at the data link layer.
LAN standards encompass Layers 1 and 2 of the OSI model. Examples of LAN standards are Ethernet and IEEE 802.3.

Front 74

What functions does the Media Access Control (MAC) sublayer provide?

Back 74

The MAC sublayer specifies how data is placed and transported over the physical wire.
It controls access to the physical medium. The LLC sublayer communicates with the network layer, but the MAC sublayer communicates downward directly to the physical layer. Physical addressing (MAC addresses), network topologies, error notification, and delivery of frames are defined at this sublayer.

Front 75

What does the LLC sublayer do?

Back 75

The Logical Link Control (802.2) sublayer is responsible for identifying different network layer protocols and then encapsulating them to be transferred across the network.
Two types of LLC frames exist: service access points (SAP) and Subnetwork Access Protocol (SNAP). An LLC header tells the data link layer what to do with a packet after it is received.

Front 76

What do the Ethernet and IEEE 802.3 standards define?

Back 76

The Ethernet and IEEE 802.3 standards define a bus-topology LAN that operates at a baseband signaling rate of 10 Mbps, referred to as 10BASE. Within the Ethernet standards are protocol specifications that define the transmission medium and access. The following three protocol specifications exist:
- 10BASE2: Known as thin Ethernet, this specification uses thin coaxial cable as its medium and provides access for multiple stations on the same segments.
- 10BASE5: Called thick Ethernet, this specification uses a thick coaxial cable as its medium. The maximum segment length of 10BASE5 is over twice that of 10BASE2.
- 10BASE-T: This specification provides access for a single station only, so all stations connect to a switch or hub. The physical topology of 10BASE-T is that of a star network. It uses unshielded twisted-pair (UTP) cable Category 3, 4, 5, and 5e as its network medium.

Front 77

Define the Fast Ethernet standard.

Back 77

The Ethernet standard that defines Fast Ethernet is IEEE 802.3u. This standard raises the speed of the Ethernet standard of 10 Mbps to 100 Mbps with only minimal changes to the existing cable structure. The Fast Ethernet standard defines different protocol specifications depending of the physical medium used. The following are the four different Fast Ethernet specifications:
- 100BASE-FX: Uses two strands of multimode fiber-optic cable as its medium and has a maximum segment length of 400 meters.
- 100BASE-T: Defines UTP as its medium and has a maximum segment length of 100 meters.
- 100BASE-T4: Uses four pairs of Cat 3 to 5 UTP as its medium. It maximum segment length is 100 meters.
- 100BASE-TX: Specifies two pairs of UTP or shielded twisted-pair (STP) cable as its medium with a maximum segment distance of 100 meters.

Front 78

What does BASE mean in 10BASE-T and 100BASE-T?

Back 78

BASE in 10BASE-T and 100BASE-T refers to the baseband signaling method. Baseband is a network technology in which only one carrier frequency is used. This means that when a device transmits, it uses the entire bandwidth on the wire and does not share it. Ethernet defined baseband technology.

Front 79

What is Gigabit Ethernet?

Back 79

Gigabit Ethernet is an extension of the IEEE 802.3 Ethernet standard. It increases the speed of the Ethernet protocol to 1000 Mbps, or 1 Gbps. IEEE 802.3z specifies Gigabit over fiber, and IEEE 802.3ab specifies Gigabit over twisted-pair cable.

Front 80

What is carrier sense multiple access collision detect (CSMA/CD)?

Back 80

CSMA/CD describes the Ethernet access method.
In CSMA/CD, many stations can transmit on the same cable, and no station has priority over any other. Before a station transmits, it listens on the wire (carrier sense) to make sure that no other station is transmitting. If no other station is transmitting, the station transmits across the wire. If a collision occurs, the transmitting stations detect the collision and run a backoff algorithm. The backoff algorithm is a random time that each station waits before retransmitting.

Front 81

What are the three ways LAN traffic is transmitted?

Back 81

LAN traffic is transmitted one of the following three ways:
- Unicast: Unicasts are the most common type of LAN traffic. A unicast frame is a frame intended for only one host.
- Broadcast: Broadcasts frames intended for everyone. Stations view broadcast frames as public service announcements. All stations receive and process broadcast frames.
- Multicast: Multicasts are traffic in which one transmitter tries to reach only a subset, or group, of the entire segment.

Front 82

How many bits are in an Ethernet address?

Back 82

48. Also called a MAC address, an Ethernet address is the Layer 2 address associated with the Ethernet network adapter. Typically burned into the adapter, the MAC address is usually displayed in a hexadecimal format, such as 00-0d-65-ac-50-7f.

Front 83

What portion of the MAC address is vendor specific?

Back 83

The first half or first 24 bits of the MAC address are vendor specific.
A MAC address is 48 bits and is displayed in hexadecimal. The first half of the address identifies the vendor or manufacturer of the card. This is called the Organizational Unique Identifier (OUI). The last half of the address identifies the card address.

Front 84

What portion of the MAC address is vendor assigned?

Back 84

The last 24 bits are vendor assigned.

Front 85

What is the maximum cable length for UTP?

Back 85

100 meters or 328 feet.

Front 86

What is a straight-through Ethernet cable, and when would you use it?

Back 86

A straight-through Ethernet cable is wired the same way at both ends. This cable uses pins 1, 2, 3, and 6. The send and receive wires are not crossed.
You should use a straight-through Ethernet cable when connecting dissimilar devices (for example, data terminal equipment [DTE] to data communications equipment [DCE]). Examples include connecting PCs (DTE) to switches or hubs (DCE) or a router (DTE) to a switch or a hub (DCE).

Front 87

What is a crossover Ethernet cable, and when would you use it?

Back 87

A crossover Ethernet cable is a cable that has the send and receive wires crossed at one of the ends. In a Category 5 cable, the 1 and 3 wires are switched and the 2 and 6 wires are switched at one end of the cable.
You should use a crossover cable when connecting similar devices (DCE to DCE), such as connecting a router to a router, a switch to a switch or hub, a hub to a hub, or a PC to a PC.