Week 1 - Introduction to Computer Networking Flashcards
Define what is a “protocol”?
A defined set of rules/standards that computers must follow in order to communicate properly
(rules of delivering a piece of mail through a delivery system)
What does computer networking generally refer to?
the full scope of how computers communicate with each other
Why are network protocols important? 2
- computers can hear and understand each other with the same protocols
- repeat messages not fully delivered
What are the 5 layers of Networking of the TCP/IP model? Top to bottom
- Application
- Transport
- Networking
- Data Link
- Physical
What is the Physical Layer?
The physical devices that interconnect computers
The delivery truck (of bits of data)
(cables, connection points, and protocols for how signals are sent)
What is the Data Link Layer also known as? What protocol is introduced? What does it specify? What type of data transfer does it focus on?
Network interface layer
introduces first protocols (ethernet, wifi) and is responsible for specifying physical layer attributes and focuses on getting data to nodes on the same network/link.
What is the Network Layer? What device does it use and how? What protocol?
Internet Layer
Gets data from one node to another in different networks using routers. Uses common Internet Protocol
What does the Transport layer do? What are common protocols in this layer? Which is the unreliable delivery? What protocol does it use to get around?
Sorts out which clients and server programs are meant to get data
Common is TCP to deliver data reliably, uses IP to get around. UDP is also common but no reliable delivery.
What is UDP?
User Datagram Protocol
Unreliable delivery of data, delivers it everywhere
How delivery truck finds your specific house
What is the Application Layer? What does its protocols allow you to do?
Applications, directly interact with this layer. The protocols allow you to browse the web or send/receive data.
The actual package you can touch (interact with)
Out of the Cat cables, which is limited in range transporting data across long distances at high speeds?
Cat 6
What is crosstalk?
when an electrical pulse is detected on another cable causing an error in the transmission of data
receiving end can’t understand data causing it to be re-sent
Which is better and why? Cat 5 or Cat 5e?
Cat 5e is better as Cat 5 is older and more susceptible to crosstalk. Cat 5e is more reliable and faster.
What are Cat cables made of? What do they do?
Twisted copper wires inside a plastic insulator that send binary signals as voltage changes in 1s and 0s
(receiving end = interprets voltages into data using line coding)
What is the benefit of fiber optic cables distance-wise?
Can transport data across long distances at higher speed without potential data loss
What are point-to-point connections?
a single device is at the end of each cable
not for multiple computers to connect
What is a Hub? What layer is it? Can it inspect contents?
a physical layer device that allows multiple computers to interconnect on a single network (LAN)
No cannot inspect data, all computers end up receiving the data (congestion)
What is a network switch? What layer is it?
it’s a data link layer device that is like a hub but is able to inspect contents of ethernet data being sent to it from a computer to determine which system is meant to receive that data
Explain what routers do? What layer are they? What do they use to help them network?
Network layer
They forward data between independent networks using IP data and internal tables
How is a core ISP router different?
a core ISP router is able to handle more traffic and more complex traffic decisions
backbone of the internet
How do routers share global data with each other? How does it work?
BGP - Border Gateway Protocol
Lets them know the optimal path to forward traffic
Google Maps GPS of the world’s networks
What is a node?
a device connected to the internet
What is a server?
serves data to clients (customers) requesting that data (asking for food)
What is a client?
requesting the data from the server (receiving food)
Can nodes be both a server and a client?
Yes, almost all nodes are both at some point most aren’t purely a server or client
Can individual computer programs on the same node be servers and clients to each other too?
Yes
like Active Server Directory
What do you call a node that is a server but also a client? Which of the two?
It depends on its primary reason
If it’s to serve data to client, it’s a server (like an email server, even though it’s a client of a DNS server)
What could also occasionally be a server in your house?
A desktop (fetches data from servers so user can do their work)
How many wires are in a standard Cat 6 cable? How many pairs?
8 wires, 4 pairs
What is full duplexing?
When data is able to flow in both directions simultaneously
What is half-duplex? What layer is it?
A half duplex connection allows communication in both directions, but only one side can communicate at a time.
Physical layer
What is simplex communication? on what medium? What layer is it?
1 way communication channel over a cable or radio signal
Physical layer
What is EMI and RFI?
Electromagnetic interference
Radio Frequency interference
What are FTP, STP, UTP cables?
FTP - foiled twisted pair
STP - shielded twisted pair
UTP - unshielded twisted pair
What is the least expensive type of Ethernet cable for home/business?
UTP unshielded twisted pair
Which two Ethernet cable types can exist together for extra protection against interference? Where is this most likely used?
STP and FTP
in industrial environments where EMI/RFI is much higher than normal (more expensive option)
Which Ethernet cable is more used for Network tasks?
CAT cables
Which Ethernet cables are used for computer/router connections to hubs and Ethernet switches
and which for server connections —> Ethernet switches?
Straight through cables
When are crossover cables used?
- connect an IT admin laptop directly to an Enterprise machine (server, switch, router, hub, etc)
- Connecting 2 similar devices together (2 switches, 2 hubs, switch to hub, 2 routers, 2 PCs, router to PC)
What is Auto-MDI/MDIX technology? What do they stand for?
Technology on an Enterprise machine that can detect Ethernet connection types and select the correct wires to send/receive data
Used to connect 2 computing devices to each other
Auto Medium Dependent Interface Crossover (Auto-MDI/MDIX) technology
How do you connect crossover cables?
connection made between:
1. Ethernet port/NIC on the IT admin system
2. the management port of the Enterprise machine
What is NIC?
Network Interface Card
Difference between straight-through cables and crossover cables? What devices do they connect to?
Straight-through cables connect dissimilar devices and crossover cables connect similar devices
What is modulation?
varying electrical charges that carry bits of data over a cable
What is line coding?
converts binary digits into a sequence of bits (turns electrical charges into something the computer can understand)
(digital data to digital signals)
What is a patch panel?
contains many network ports, main purpose
Which Ethernet TP cable is most common?
Unshielded Twisted Pair
basic protection, least expensive
Which Ethernet TP cable uses braided aluminum and copper to encase 4 twisted pairs?
Shielded Twisted Pair
uses braided aluminum and copper shielding
Which Ethernet TP cable uses a thin foil shield wrapped around bundle of TP wires?
Foiled Twisted Pair
Which TP cables can exist together in same cable for extra protection against interference?
STP and FTP
What is a collision domain?
A network segment where only one device can speak at a time
(packets collide from congestion)
What is the Ethernet protocol?
protocol most widely used to send data across individual links
What does CSMA/CD do? What does it stand for?
Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
determines when a communication channel is clear so a device is free to transmit data
What happens if the CSMA/CD detects a data collision?
It stops sending data temporarily, waits a random interval of time and starts sending data again to avoid another collision
What is a MAC address and what is it attached to?
a globally unique identifier attached to an individual network node (like a computer, PlayStation, etc)
(the address to a house)
How many bits in a MAC address?
48-bit number represented by 6 groupings (6 numbers in a group) of 2 hexadecimal numbers
EX) 00 60 2F
EX) 3A 07 BC
What is hexadecimal?
hexadecimal represents #s with a 16 digit range (the whole table 0-9 and A-F)
EX) 01 68 7E
EX) 2B 04 CD
What is an octet?
In computer networking, 8 bits (a byte) represented by a #
00 60 28
Each number is an octet/byte (48 bits in total)
What are the first 3 octets in a MAC address assigned by? And to who?
Assigned by the IEEE to individual network hardware manufacturers (institute of electrical and electronics engineers)
What are the last 3 octets of a MAC address assigned by?
Assigned any way a manufacturer would like with the condition that they only assign each possible address once to keep all MAC addresses globally unique
How does the Ethernet protocol use MAC addresses?
The Ethernet protocol uses MAC addresses:
1. to ensure the data it sends has an address for the machine that sent the data
2. an address for the machine that data is intended for
What does it mean when a network segment is a collision domain?
all devices on that segment receive all communication across the entire segment
also:
network congestion
collision of data packets
1 device can transmit data at a time
What 2 sections are MAC addresses split into?
- OUI (organizationally unique identifier) - first 3-hexa bytes/octets of MAC address assigned by the IEEE to individual hardware manufacturer’s
- The manufacturer uses the last 3-hexa bytes to generate unique MAC addresses for every interface.
What does OUI stand for in MAC addresses?
Organizationally Unique Identifier
What are the 3 types of Ethernet transmissions?
- Unicast
- Multicast frame
- Broadcast using a broadcast address
What is a broadcast address? How do they look?
It’s a special destination used by the broadcast Ethernet transmission to send data to every device on a LAN.
The Ethernet broadcast address is all F’s (set to 1s)
Why are Ethernet broadcast addresses used?
So devices can learn more about each other (like their MAC address)
How many addresses receive the Unicast Ethernet transmission?
1, always meant for one receiving address
How do Ethernet transmissions work by looking at a special bit in the MAC address? 2 different types of transmissions looked at
- If first octet’s least significant bit is set to 0, means the ethernet frame is UNICAST and intended for only the destination address (sent to all devices on CD, but only received and processed by the intended destination)
- If the first octet’s least significant bit is set to 1, it means you’re dealing with a MULTICAST frame.
What did the Ethernet protocol use to solve the data collision issue?
using a technique known as CSMA/CD
Carrier Sense Multiple Access with Collision Detection
What is a benefit of twisted wires?
Reduces noise and is less susceptible to cross talk
What sort of applications use twisted pair cabling technology?
audio, security, alarm, network Ethernet cables
What happens in the area between two parallel wires that are carrying current in opposite directions?
a magnetic field is created
What does MAC stand for?
Media Access Control
In what layer do MAC address work in?
The data link layer
What are the differences between Unicast, Multicast, and Broadcast addresses? 3
What do they send?
- Unicast: The packet is sent to a single destination (one-to-one)
- Multicast: The packet is sent to a set (group) of hosts that can be on different networks (one to many)
- Broadcast: The packet is sent to an entire network (one to all) with a broadcast address
Why are Ethernet broadcast addresses used?
So devices can learn more about each other (like their MAC address)
What is a data packet?
general concept of data sent from A to B, no specific layer
What are data packets at an Ethernet level called? What are they?
Ethernet Frames
collection of highly structured info presented in a specific order
How do Ethernet frames work with physical layer network interfaces?
The network interfaces convert the streams of bits into meaningful data (vice versa)
Are all sections of an Ethernet frame mandatory?
Almost all are mandatory and most have a fixed size
What are the 8 sections of an Ethernet frame?
- Preamble
- SFD (start frame delimiter)
- Destination MAC address
- Source MAC address
- VLAN header
- Ether-type
- Payload
- FCS (frame check sequence)
What is a preamble? Can it be split?
First section of an Ethernet frame and can be split into 2 sections
- First 7 bytes act as buffer and synchronize the internal clocks frames use (regulates data speed)
- SFD
What is SFD in the preamble? What does it do?
signals to receiving device that the preamble is over and the actual frame contents will now follow
Start Frame Delimiter
What is the Ether-type field?
describes the protocol of the contents of the frame (2 bytes long)
What could we also find instead of an Ether-type field in a frame?
VLAN header (indicates the frame is a VLAN frame)
Ether-type field follows it
How are frames with VLAN delivered?
Only delivered out of a switch interface configured to relay that specific VLAN tag
What is a VLAN?
Virtual LAN
technique that lets you have multiple LANs operating on the same physical equipment
What do VLANs separate?
separate different groups of traffic and devices (IP phones on one VLAN, all desktops on another, etc)
What data does the data payload transport? (46-1500 bytes long)
Everything from the higher layers (IP, Transport, Application) that isn’t a header
What does FCS stand for?
Frame Check Sequence
What is the FCS (frame check sequence) in an Ethernet frame?
a 4 byte number that represents a checksum value for the entire frame
How is a checksum value calculated?
performs a CRC (cyclical redundancy check) against the frame
Performing a CRC against a set of data should give you the same checksum number every time
What does the CRC do?
CRC Cyclical Redundancy Check
Included in an Ethernet frame so receiving network interface can see if it received corrupted data
When does a network device throw out the data received?
When the checksum number it calculated does not match the frame check sequence number that was attached to the end of the frame
Does Ethernet perform data recovery?
No, only performs data integrity checks
Why are MAC addresses useful?
Using MAC addresses prevents the network segment from becoming a collision domain
