OBJ 1.1 X

Question 1

OSI Model Layers

Answer 1

1. Physical
2. Data link
3. Network
4. Transport
5. Session
6. Presentation
7. Application

Question 2

Ethernet Header

Answer 2

Fields in a frame used to identify source and destination MAC addresses, protocol type, and error detection.

Question 3

TCP (transmission control protocol)

Answer 3

Protocol in the TCP/IP suite operating at the transport layer to provide connection-oriented, guaranteed delivery of packets.

Question 4

UDP (user datagram protocol)

Answer 4

Protocol in the TCP/IP suite operating at the transport layer to provide connectionless, non-guaranteed communication.

Question 5

TCP Flags

Answer 5

Field in the header of a TCP segment designating the connection state, such as SYN, ACK, or FIN.

Question 6

Internet Protocol (IP) Header

Answer 6

Fields in a datagram used to identify source and destination IP addresses, protocol type, and other layer 3 properties.

Question 7

MTU (Maximum transmission unit)

Answer 7

Maximum size in bytes of a frame’s payload. If the payload cannot be encapsulated within a single frame at the Data Link layer, it must be fragmented.

Question 8

1. Physical Layer

Answer 8

Transmission of bits across the network.

Question 9

2. Data link layer

Answer 9

Packages data into frames and transmitting those frames on the network, performing error detection/correction, and uniquely identifying network devices with an address (MAC), and flow control

Question 10

3. Network layer

Answer 10

Forwards traffic (routing) with logical address. (example: IP address IPv4 or IPv6)

Question 11

4. Transport layer

Answer 11

Dividing line between upper and lower layers of the OSI model. Data is sent as segments.

Question 12

5. Session layer

Answer 12

Think of a session as a conversation that must be kept separate from others to prevent intermingling of the data. Setting up, maintaining, and tearing down sessions.

Question 13

6. Presentation layer

Answer 13

Responsible for formatting the data exchanged and securing that data with proper encryption.

Question 14

7. Application layer

Answer 14

Provides application-level services. The layer where the users communicate with the computer.

Question 15

1. Physical layer (How are bits represented on the medium?)

Answer 15

Electrical voltage ((copper wiring) or light (fiber optics) represents 1’s and 0’s (bits) If 0 volts, then 0 is represented. If +/-5 volts, then 1 is represented.

Transition modulation: If it changed during the clock cycle, then a 1 is represented, otherwise, a 0.

Question 16

1. Physical layer (How are the cables wired?)

Answer 16

TIA/EIA-568-B is standard wiring for RJ-45 cables and ports. Crossover cables use T-568A and T-568B. Straight thru cables typically use T-568 B on both ends, but could use T-568A on both.

Question 17

1. Physical layer (How are the cables connected?)

Answer 17

Layer 1 devices view networks from a physical topology perspective. Bus, Ring, Star, Hub-and-Spoke, Full Mesh, Partial Mesh

Question 18

1. Physical layer (How is communication synchronized?)

Answer 18

Asynchronous: uses start bits and stop bits to indicate when transmissions occur from sender to receiver

Synchronous: Uses a reference clock to coordinate the transmissions by both sender and receiver.

Question 19

1. Physical layer (examples)

Answer 19

Cables (ethernet, fiber optic)
Radio frequencies (Wi-Fi, bluetooth)
Infrastructure devices (hubs, wireless access points, media converters)

Question 20

2. Data link layer (physical addressing)

Answer 20

Physical addressing
uses 48-bit address assigned to a network interface card by manufacturer. First 24 bits is the vendor code, second 24-bits is a unique value.

Question 21

2. Data link layer (logical topology)

Answer 21

Layer 2 devices view networks logically (ring, bus, star, mesh, hub-and-spoke)

Question 22

2. Data link layer examples

Answer 22

Network Interface Cards, Bridges, Switches

Question 23

3. Network Layer (Logical addressing)

Answer 23

Numerous routed protocols were used for logical addressing over the years. (AppleTalk, IPX, IP) Only IP remains dominant. IP v4, IP v6

Question 24

3. Network Layer (how data should be forwarded or routed?)

Answer 24

Packet switching (routing) where data is divided into packets and forwarded.

Circuit switching - dedicated communication link is established between two devices.

Message switching (data is divided into messages, similar to packet switching, except these messages may be stored then forwarded

Question 25

3. Network layer (route discovery and selection)

Answer 25

Routers maintain a routing table to understand how to forward a packet based on destination IP address. Manually configured as a static route or dynamically through a routing protocol. (RIP, OSPF, EIGRP)

Question 26

ICMP

Answer 26

Internet Control Message Protocol (ICMP) used to send error messages and operational information about an IP destination. Not regularly used by end-user applications, used in troubleshooting (ping and traceroute)

Question 27

3. Network Layer examples

Answer 27

Routers, Multilayer swtiches, IPv4 protocol, IPv6 protocol, ICMP

Question 28

TCP (transmission control protocol) (L4)

Answer 28

Connection-oriented, reliable transport of segments, (if segment is dropped, protocol detects it and resends segment), acknowledgements received for successful communications, used for all network data that needs to be assured to get to its destination

Question 29

UDP (user datagram protocol) (L4)

Answer 29

Connectionless protocol, unreliable transport of segments, (if dropped, sender is unaware), no retransmission, good for audio/video streaming, lower overhead for increased performance.

Question 30

Windowing (L4)

Answer 30

Allows the clients to adjust the amount of data sent in each segment, continually adjusts to send more or less data per segment transmitted. Adjusts lower as number of retransmissions occur, adjusts upwards as retransmissions are eliminated.

Question 31

Buffering (L4)

Answer 31

Devices, such as routers, allocate memory to store segments if bandwidth isn't readily available. When available, it transmits the contents of the buffer, if the buffer overflows, segments will be dropped.

Question 32

4. Transport Layer examples

Answer 32

TCP, UPD, WAN Accelerators, Load Balancers, Firewalls

Question 33

5. Session Layer (set up, maintain, tear down)

Answer 33

Setting up - check user credentials, assign numbers to session to identify them, negotiate services needed for session, negotiate who begins sending data. Maintaining - transfer the data, reestablish a disconnected session, acknowledging receipt of data Tearing down a session - due to mutual agreement (after the transfer is done), due to the other party disconnecting the session

Question 34

5. Session layer examples

Answer 34

H.323 (used to setup, maintain, and tear down a voice/video connection) NetBIOS (used by computers to share files over a network)

Question 35

6. Presentation Layer (Data formatting, Encryption)

Answer 35

Data formatting - formats data for proper compatibility between devices, ASCII, GIF, JPG, ensures data is readable by receiving system, provides proper data structures, negotiates data transfer syntax for the application layer (7) Encryption - Used to scramble the data in transit to keep it secure from prying eyes.

Question 36

6. Presentation layer examples

Answer 36

HTML, XML, PHP, JAVASCRIPT, ASCII, EBCDIC, UNICODE, GIF, JPG, TIF, SVG, PNG, MGP, MOV, TLS, SSL

Question 37

7. Application layer (App services, Service Advertisement)

Answer 37

Application services - unite communicating components from more than one network application. Ex: file transfers and sharing, e-mail, remote access, network mgmt activities, client/server processes. Service Advertisement - some apps send out announcements, states the services they offer on the network, some centrally register with Active Directory server instead (printers, file servers)

Question 38

7. Application layer examples

Answer 38

E-mail (POP3, IMAP, SMPT) Web browsing (HTTP, HTTPS) DNS< FTP< FTPS< TELNET< SSH< SNMP

Question 39

Encapsulation

Answer 39

the process of putting headers (and sometimes trailers) around some data

Question 40

Decapsulation

Answer 40

Action of removing the encapsulation that was applied. If we move down the OSI layers from 7 to 1, we ENCAPSULATE data If we move upward from layers 1 to 7 we DECAPSULATE data

Question 41

Protocol data unit

Answer 41

a single unit of info transmitted within a computer network Layer 1 - bits Layer 2 - frames Layer 3 - packets Layer 4 - segments if TCP or datagrams if UDP

Question 42

SYN (synchronization flag)

Answer 42

The most well-known flag in TCP communications because it is used to synchronize the connection during the three-way handshake

Question 43

ACK (or acknowledgement) flag

Answer 43

Used during the three-way handshake, but it is also used to acknowledge the successful receipt of packets

Question 44

FIN (or finished) packet

Answer 44

-Used to tear down the virtual connections created using the three-way handshake and the SYN flag -The FIN flag always appears when the last packets are exchanged between a client and server and the host is ready to shutdown the connection

Question 45

RST (or reset) flag

Answer 45

▪ Used when a client or server receives a packet that it was not expecting during the current connection

Question 46

PSH (or PUSH) flag

Answer 46

Used to ensure that the data is given priority and is processed at the sending or receiving ends

Question 47

URG (or urgent) flag

Answer 47

It is like the Push flag and identifies incoming data as “urgent” The main difference is PSH is used by a sender to indicate data with a higher priority level where URG is sent to tell the recipient to process it immediately and ignore anything else in queue