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2019 Network+ N10-007 CompTIA > 1.2, 1.3 – OSI Layers, Etc. > Flashcards

1.2, 1.3 – OSI Layers, Etc. Flashcards

1
Q

What is OSI Layer 1?

A

Physical

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2
Q

What is OSI Layer 2?

A

Data link

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3
Q

What is OSI Layer 3?

A

Network

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4
Q

What is OSI Layer 4?

A

Transport

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5
Q

What is OSI Layer 5?

A

Session

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6
Q

What is OSI Layer 6?

A

Presentation

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7
Q

What is OSI Layer 7?

A

Application

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8
Q

Which OSI Layer is this?

Physical

A

Layer 1

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9
Q

Which OSI Layer is this?

Data link

A

Layer 2

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10
Q

Which OSI Layer is this?

Network

A

Layer 3

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11
Q

Which OSI Layer is this?

Transport

A

Layer 4

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12
Q

Which OSI Layer is this?

Session

A

Layer 5

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13
Q

Which OSI Layer is this?

Presentation

A

Layer 6

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14
Q

Which OSI Layer is this?

Application

A

Layer 7

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15
Q

What does OSI stand for?

A

Open Systems Interconnection Reference Model

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16
Q

What does the physical layer pertain to?

A

The physics of the network. The signal, the cabling, and connectors.

There are no protocols involved in Layer 1.

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17
Q

What does the data link layer pertain to?

A

The “switching” layer.

The basic network language. The most fundamental communication that occurs across the network.

The frames of communication.

Data Link Control (DLC) protocols.

MAC addresses.

Extended Unique Identifiers

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18
Q

What does the Network layer pertain to?

A

The “routing” layer.

An IP layer. If dealing with any type of IP address, you’re working at Layer 3.

Also responsible for fragmenting frames to traverse different networks, when smaller packets are needed.

IP address, router, packet.

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19
Q

What does the Transport layer pertain to?

A

The “post office” layer.

Transfers information to a destination.

Port numbers.

TCP segment. UDP datagram.

The most common protocols are TCP and UDP.

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20
Q

What does the Session layer pertain to?

A

Communication management between devices.

Start, stop, and restart sessions.

Control protocols, and tunneling protocols.

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21
Q

What does the Presentation layer pertain to?

A

Character encoding

Encryption. Any data that needs to be encrypted or decrypted usually occurs in the Application at Layer 6.

SSL, TLS

Many of the applications that are working at Layer 6 may also be working at Layer 7. So, many Applications share both Layer 6 and Layer 7.

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22
Q

What does the Application layer pertain to?

A

The layer we see.

A browser window, etc.

Application Services are on Layer 7. Protocols are things like HTTP, FTP, SSH, DNS, SMTP, POP, IMAP, SNMP.

Service Advertisements are on Layer 7.

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23
Q

What is an OUI?

A

Organizationally Unique Identifier

The first three bytes (first six characters) of a MAC address, which is associated with the manufacturer of the Ethernet adapter.

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24
Q

In Ethernet, what is a collision?

A

In half-duplex mode Ethernet, if two devices communicate simultaneously, the two frames create a collision.

Each device on the network will “hear” that collision (a jam signal will be transmitted across the network), and wait a random amount of time before attempting to communicate again.

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25
Q

What is CSMA/CD?

A

It is no longer in use. It was used only in Half-duplex Ethernet.

CS: Carrier Sense

  • The Ethernet adapter determines whether there is a carrier for it to transmit a signal over.
  • Listen to the wire, determine if busy

MA: Multiple Access
- indicates there is more than one device on the network, and all devices have access at any time (as opposed to a token ring)

CD: Collision Detect
- If a collision occurs, the devices can recognize that, back off for a random amount of time (milliseconds), and attempt to transmit again.

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26
Q

What is the order of operations for CSMA/CD?

A

1) Listen for an opening (don’t transmit if the network is busy)
2) Send a frame of data.

3) If a collision occurs:
- Transmit a jam signal to notify all devices of collision
- Wait a random amount of time (milliseconds)
- Retry the transmission

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27
Q

What is CSMA/CA?

A

CS: Carrier Sense

MA: Multiple Access

CA: Collision Avoidance

Common on wireless networks.

When a wireless device is sending information, it is unable to receive anything or be aware of incoming transmissions. Therefore, collision detection is not possible.

28
Q

How does CSMA/CA operate?

A

Using RTS/CTS

A device will send a “Ready To Send” signal to a wireless access point. The wireless will send back a “Clear To Send” signal, indicating that the client device may now send data.

When this system is in use, the wireless access point will only accept data from a device it has already sent a CTS to.

29
Q

How does a switch know where to send traffic it receives for a specified destination device?

A

I uses the destination’s MAC address, which will be specified by the Ethernet frame.

A switch maintains a MAC Address Table, where it maps every MAC Address it receives communication from to the the particular interface on the Switch that it’s located behind.

Traffic may need to go through multiple switches to reach a destination, and each switch will only know the “next step”, i.e., which of its own interfaces to send it out through.

30
Q

What happens if a switch receives traffic for a destination that isn’t recorded in its MAC Address Table?

A

The switch will send the frame to everyone (that is, out through all of its connected interfaces.)

31
Q

What is ARP?

A

Address Resolution Protocol

A broadcast request for a MAC address based on an IP address.

32
Q

What is a Collision Domain?

A

A segment of a half-duplex network that has been segregated via a switch or bridge, so that collisions can occur on one segment without disrupting traffic on the other segment.

Each of these segments is their own “Collision Domain.” If a Collision occurs, all traffic within the same Collision Domain is stopped.

33
Q

What is a Broadcast Domain?

A

The segment of a network that a Broadcast frame will be able to pass through.

Switches and bridges will pass on Broadcast frames through all of their interfaces.

Broadcasts will not be able to pass through a router.

34
Q

What is a PDU?

A

Protocol Data Unit

A unit of information that is sent by a protocol at a particular OSI layer.

Different layers will have different protocols and PDUs.

35
Q

What is an MTU?

A

Maximum Transmission Unit

The maximum IP packet size that can be transmitted without being fragmented.

On supported devices, the value of this can be set administratively, but all devices must be set to the same value.

36
Q

What is the PDU of TCP?

A

A TCP Segment

also just called a “segment.”

37
Q

What is the PDU of UDP?

A

UDP datagram

38
Q

What is the Layer 3 PDU?

A

A “Packet”

An IP Packet

39
Q

What is the Layer 2 PDU?

A

A “Frame”

also called a “Data Link Frame”

40
Q

What is the default maximum amount of TCP data you can normally send in an Ethernet frame?

A

1460 bytes

41
Q

What is the default maximum size of an Ethernet frame?

A

1500 bytes

42
Q

What possible VLAN IDs are there?

A

The VLAN header in 801.1Q is 12 bits long, therefore you have 4096 possible IDs.

0 and 4095 are reserved and cannot be assigned.

1 through 1005 are “normal range” VLAN IDs.

1006 though 4094 are sometimes distinguished as “extended range” VLAN IDs, and sometimes included in the normal range.

43
Q

In the context of network devices, what is STP?

A

Spanning Tree Protocol

The IEEE standard is 802.1D.

Designed to prevent loops in bridged (switched) networks. at the MAC layer.

It automatically and dynamically configures itself across multiple STP-enabled switches in a network.

44
Q

What is a VLAN?

A

Virtual Local Area Network

A network that has been separated logically instead of physically. Devices on the same physical network can be in separate broadcast domains.

45
Q

What is 801.1Q?

A

The standard for Ethernet Trunking. Also called a “dot 1Q trunk.”

It adds a VLAN header into the Ethernet Frame, so multiple VLANs can be identified between switches.

46
Q

What is a network loop?

A

If devices are connected in such a way that they have more than one path between each other, they’ll could send traffic back and forth forever.

For example, two switches connected to each other with two cables.

This is because there is no “counting” mechanism at the MAC layer, to determine if traffic has been passed too many times.

It will very quickly overwhelm the capabilities of the switches and bring down the network, almost immediately.

47
Q

What is IEEE standard 802.1D?

A

The Spanning Tree Protocol

48
Q

What types of interfaces will STP automatically configure?

A

Root Port
- each switch has one root port, which is the interface that is the closest to the Root Switch (each STP network has only one root switch, also auto-determined by STP).

Designated Port
- a port that traffic is allowed to traverse.

Blocked Port
- STP has automatically blocked the port to prevent a loop

49
Q

What is RSTP?

A

Rapid Spanning Tree Protocol

802.1w

An updated version of STP, the current latest standard.

Provides faster convergence.

Backwards compatible with STP.

50
Q

How long does convergence take in STP?

A

30-50 seconds for STP.

6 seconds for RSTP.

51
Q

What is a SPAN port?

A

Switch Port Analyzer

A SPAN port is the destination that mirrored ports will copy their traffic to.

52
Q

Difference between PoE and PoE+?

A

PoE:
• introduced in 2003
• 15.4 watts of DC power
• Max current of 350 mA

PoE+:
• introduced in 2009
• 25.5 watts of DC power
• Max current of 600 mA

53
Q

What is ARP?

A

Address Resolution Protocol

Determine a MAC address based on an IP address.

54
Q

What is Dynamic Routing, and how does it work?

A
  • Routers send routes to other routers.
  • Routing tables are updated in almost real-time.
  • New routes are populated automatically.
  • Very scalable, good with larger networks
  • Some overhead required (CPU, memory, bandwidth).
55
Q

What is a Default Route?

A

When configured, the Default Route will be the route used when no other route matches.

  • The “gateway of last resort.”
  • Particularly useful when there’s only one way out of a network, can simplify the routing process.
  • Works in conjunction with all other routing methods.
56
Q

What is IEEE standard 802.1D?

A

Spanning Tree Protocol

57
Q

List examples of Layer 7 Protocols

A

HTTP

POP, IMAP, SMTP

SNMP

FTP

SSH

DNS

58
Q

What is:

ASCII

A

American Standard Code for Information Exchange

Data formatting, which exists at Layer 6 (Presentation)

59
Q

List examples of things that operate at Layer 6

A

• Scripting languages:
HTML, XML, PHP, JavaScript

• Text Formats:
ASCII, Unicode

• Movie formats:
MPG, MOV

• Image formats:
GIF, JPG, TIF, PNG

• Encryption:
TLS, SSL

60
Q

What is the TCP/IP Model?

A

An alternative to the OSI model, which is less ambiguous and more relevant since all modern networks are based on TCP/IP.

61
Q

What are the layers of the TCP/IP Model?

A

Layer 1: Network Interface

Layer 2: Internet

Layer 3: Transport

Layer 4: Application

62
Q

What OSI Layers are Included in TCP/IP Layer 4?

A

The TCP/IP Application Layer encompasses the equivalent of these OSI Layers:

Session
Presentation
Application

63
Q

What OSI Layers are Included in TCP/IP Layer 3?

A

The TCP/IP Transport Layer encompasses the equivalent of this OSI Layer:

Transport

(a direct equivalency)

64
Q

What OSI Layers are Included in TCP/IP Layer 2?

A

The TCP/IP Internet Layer encompasses the equivalent of this OSI Layer:

Network

(almost a direct equivalency, although the TCP/IP layer focuses more on routing to external networks)

65
Q

What OSI Layers are Included in TCP/IP Layer 1?

A

The TCP/IP Network Interface Layer encompasses the equivalent of these OSI Layers:

Physical
Data Link

66
Q

In STP, how is a root port determined?

A

Every non-root bridge has a single root port.

The port closest to the root bridge, in terms of cost, will be set as the root port. (Costs are determined by cable type, throughput, etc.)

If costs are equal, the lowest number port is chosen.

2019 Network+ N10-007 CompTIA (7 decks)

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