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final Flashcards

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1
Q

end systems are connected by a network of (2):

A

communication links & packet switches

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2
Q

TF: all activity in the internet that involves 2+ communicating remote entities requires a governing protocol

A

true

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3
Q

forwarding table definition

A

part of a router that maps destination addresses to that router’s outbound links

in EVERY router

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4
Q

what are the 4 sources of packet delay and when do they occur?

A

processing = occurs when a packet first arrives; the time it takes to look at packet’s header & determine where to direct it

queuing = occurs once a packet has been processed; the time a packet spends waiting in the queue before being transmitted

transmission = occurs when sending a packet; the time required to push all the packet’s bits into the outgoing link

propagation = occurs when the packet is traveling to the next router/destination; the time it takes to move across a link

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5
Q

packet-switching definition

A

method of sending data where data is broken into small packets that are reassembled at the destination

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6
Q

circuit-switching definition & flaw

A

method of communication where a dedicated transmission link between sender & receiver stays open for the entire conversation

flaw: pre-allocates use of the transmission link regardless of demand, so unneeded link time goes unused

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7
Q

what are the 5 layers of the TCP/IP model? what does each handle?

A

5 - application - user-facing services/apps
4 - transport - end-to-end communication
3 - network - routing across networks
2 - link - data transfer between local devices
1 - physical - transmission of raw bits

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8
Q

encapsulation meaning

A

process of creating a packet by taking a data unit from the above layer

includes 2 fields: payload and header (payload = a packet from the layer above)

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9
Q

what is an ‘object’ in networking?

A

content served by a web server (e.g. HTML file, JPEG image, Java applet)

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10
Q

HTTP - client vs server side

A

client side = the device/app that sends a request for data (HTTP initiates the connection and processes the server’s response)
- e.g. a web browser asks a server for a webpage

server side = the system that receives the request and responds (HTTP waits for requests, processes them, and returns data)
- e.g. a web server like Apache hosting a website

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11
Q

TF: web servers implement the server side of HTTP

A

true

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12
Q

3 parts of a URL

A

protocol - how the data will be transferred (e.g. http:// or https://)

domain name - the server/website address (www.example.com)

path - the location of a specific resource on the server, starts with / (e.g. “/about-us”)

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13
Q

TF: the first line of an HTTP request message is called the request line

A

true

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14
Q

‘stateless’ server meaning

A

erver doesn’t remember any info from previous interactions with clients

each request is treated independently, without knowledge of prior requests

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15
Q

TF: HTTP servers are stateless

A

true: if a user logs into a website, the HTTP server won’t remember them unless the client sends additional info (like a cookie) with each request

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16
Q

another name for proxy server

A

web cache

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17
Q

proxy server and its benefits

A

network entity that satisfies HTTP requests on the behalf of a web server

benefits = speeds up web browsing because frequently accessed content doesn’t have to load, can substantially reduce traffic on an access link to the internet

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18
Q

HTTP mechanism that allows a cache to verify its objects are up-to-date is called:

A

conditional GET

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19
Q

does HTTP use UDP or TCP connections?

A

TCP

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20
Q

what are the 3 major components of email?

A

user agents
mail servers
SMTP

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21
Q

what does SMTP stand for?

A

Simple Mail Transfer Protocol

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22
Q

SMTP definition

A

protocol used to send and relay emails between computers (primarily a “push” protocol)

uses TCP for reliable delivery from sender’s mail server to recipient’s mail server

uses a command-response interaction

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23
Q

what are the 3 popular mail access protocols? + brief descriptions

A

POP3 - very simple: downloads emails to device and deletes them automatically from server (1 device)

IMAP - keeps emails on the server (multi-device) (e.g. Gmail app)

HTTP - emails are stored & accessed via web interface (e.g. gmail.com)

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24
Q

does POP3 require authorization (username/password)?

A

yes, even though it’s simple it still requires authorization

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25
logical communication meaning
from an application's perspective, it is as if the hosts running the processes are directly linked
26
what are transport-layer packets called
segments
27
what are link-layer packets called
frames
28
TF: every host on the internet has an IP address
true
29
TF: the UDP segment structure includes header fields for source and destination IP address
false; it contains source & dest port headers, but not IP TCP doesn't either?
30
how many timers does the TCP sender use to decide when to retransmit a packet?
only one: for the oldest unacknowledged packet
31
TF: the sequence number for a segment is the byte-stream number of the first byte in the segment
true
32
If TCP detects a missing packet, what does it do?
immediately sends a duplicate ACK, indicating the sequence number of the next expected byte
33
TF: in a TCP connection between Hosts A and B, the ACK number that Host A puts in its segment is the sequence number of the last byte A received from B
false; the ACK number is the sequence number of the NEXT byte A expects to receive from B
34
what are 2 things that congestion can cause?
long delays (queuing in router buffers) packet loss (buffer overflow at routers)
35
forwarding vs routing
fowarding = router-local action moving a packet from the router's input link to the appropriate output link interface (data plane) routing = network-wide process of determining the end-to-end paths for packets to travel from source to destination (control plane)
36
switching fabric
area/component that connects a router's input ports to its output ports
37
forwarding table definition
list used by a router to decide which device (next hop) to send a packet to, based on its dest IP address on the data plane
38
data plane vs control plane
control plane - routing (deciding where packets should go) - runs in software data plane - forwarding (actually sends the packets) - runs in hardware
39
interface definition
the boundary between the host and the physical link combination of hardware and software e.g. physical port you plug Ethernet into, WiFi card
40
what does NAT stand for? what does it do?
Network Address Translation maps many private (local) IP addresses to a single public IP address, so to the outside world it looks like the private network uses only 1 IP address
41
benefit of NAT
conserves IPv4 addresses by allowing many devices to share a smaller number of public IPs
42
what does DHCP stand for, and what does it do?
Dynamic Host Configuration Protocol automatically assigns an IP address to each device on a network also provides config info to hosts/clients such as its subnet mask, address of first-hop router, and address of local DNS server
43
what layer do link-layer protocols run at?
layer 2
44
what term means the same thing as "network adapter"? what does it do?
Network interface card (NIC) device inside computer that lets it send and receive data over a network each NIC has a unique MAC address
45
TF: in a one-bit even parity scheme, when an even number of bit errors occurs, the error is undetected
true
46
TF: the link layer is a combination of software, hardware, and firmware
true
47
Over HTTP, a response that the request has succeeded, or OK, uses which code number?
200
48
Does DNS run over TCP or UDP?
UDP
49
TCP and UDP definitions
both are transport-layer protocols that deliver data between applications TCP - connection-oriented, reliable, slower, correct order, error correction - used for web browsing, email, file transfer UDP - connectionless, unreliable, faster, no ordering, error DETECTION but not correction - used for video streaming, gaming
50
Tool that can intercept and log traffic passing over a digital network/part of a network
packet sniffer
51
when a socket is created, what type of identifier is associated with it?
port number
52
what is the purpose of TTL in DNS records?
to specify how long a cached entry remains valid
53
Client-server vs P2P architecture
client-server: network model where clients request services from a central server has centralized control (data = stored & managed by a server), can get congested, easy maintenance (emails, websites, cloud-based apps) P2P: all nodes (peers) communicate directly, no central control, doesn't get congested, difficult maintenance (BitTorrent, media streaming)
54
Name for packets at application layer
messages
55
What info is needed to identify a process for receiving messages over a network?
both the IP address and port number
56
TF: the Traceroute command lists all the times from transmission, propagation, processing, and queuing delays
true
57
purpose of conditional GET in HTTP
reduce response time and link utilization
58
TF: the internet's core contains packet switches
true
59
in order to transmit data over a network, an application process creates a:
socket
60
socket definition
combination of an IP address and a port number that identifies where network data should go endpoint for sending/receiving data between 2 devices on a network
61
Why isn't DNS centralized?
it wouldn't scale due to traffic volume and single point of failure
62
DNS definition
Domain Name System - phonebook of the internet, domain name resolution translates domain names to IP addresses (e.g. google.com to 142.250.190.4) if a user types 'google.com', the system sends a DNS request
63
root name server definition
first stop in a DNS lookup, helps find the right TLD server 13 servers that contain records pointing to the top-level domain (TLD) servers
64
TLD server definition
Top-Level Domain server - DNS server that handles the last part of a domain name (.com, .org, .net, etc) contains record pointing to authoritative name servers (e.g. .edu TLD server has record pointing to authoritative name servers for psu.edu)
65
What is the purpose of authoritative name servers?
controlled by domain owner (organization/indiviudal), contains the most accurate, up-to-date records for the domain e.g. Amazon.com authoritative name server contains type A records (IP addresses), and MX records (mail servers) for amazon.com
66
What is the purpose of a user's local name server?
retrieves records from authoritative name servers and caches the results so that future lookups can be performed more quickly user will automatically send all DNS queries to local name server
67
How do entries get added to the global DNS system?
domain name registrars - company/organization that maintains Internet domain reservations registrars must be accredited and follow specific processes/procedures
68
what is half-duplex/full-duplex? are TCP and UDP half- or full-duplex?
half duplex - nodes can send or receive, but not at the same time (like a walkie-talkie) full duplex - nodes can send and receive at the same time (like a phone call) both TCP and UDP are full-duplex
69
Why is the UDP header 'length' field needed?
the payload section can be of variable length, so this lets UDP know where the segment ends
70
port scanner use
tool that finds open ports on hosts/servers
71
TF: a TCP segment contains the source and dest IP address in its header fields
no, it contains the source & dest ports
72
what does the header checksum field do?
ensures data integrity
73
purpose/operation of the TCP flow control mechanism
flow control - eliminate the possibility of the sender overflowing the receiver's buffer matches sender's rate of sending against the receiving application's rate of reading sender maintains variable called the receive window, which is included in the header of every segment the receiver sends to the sender
74
purpose/operation of the TCP congestion control mechanism
congestion control - has each sender limit the rate at which it sends traffic into its connection sender maintains a variable called the congestion window, which limits the amount of unacknowledged data at the sender and indirectly limits the sender's send rate
75
main difference between TCP flow control & congestion control
flow control - prevents overwhelming the receiver, varies according to the TCP receiver's buffer space - receiver tells sender, "I can only handle 2048 bytes" congestion control - prevents overloading the network, varies according to network-wide conditions - TCP slows down when packets are lost due to congestion
76
TF: ethernet and wireless LANs are broadcast link-layer technologies
true
77
What types of structure does an IP address and MAC address have?
IP = hierarchical MAC = flat
78
What layer do switches have to process frames up through?
layer 2 (link)
79
Is it possible for an adapter to receive a frame that isn't specifically addressed to it?
yes
80
when a host's frames are forwarded by a switch, is the host aware of the existence of that switch?
no
81
what do you call the payload of an Ethernet frame?
a datagram
82
TF: If a switch receives a frame, but doesn't have an entry for the destination in its switch table, it will forward the frame on all of its interfaces except for the arriving interface.
true
83
TF: in an HTTP transaction, the client always initiates the message exchange
true
84
TF: HTTP response messages never contain status codes.
false; all HTTP response messages contain status codes
85
The first 24 out of 48 bits of a MAC address are:
unique to each manufacturer
86
what type of message reaches every device on a network?
broadcast
87
What layer uses MAC addresses? What layer uses IP addresses?
link layer (2) = MAC addresses network layer (3) = IP addresses
88
What is a flipped bit?
a bit that was erroneously changed
89
What are IP addresses most useful for?
routing
90
What does DHCP typically assign to a client?
subnet mask, DNS server, IP address
91
TF: ARP is used to translate between private & public IP addresses
false
92
about how many IPv4 addresses can there be?
around 4.3 billion
93
ARP definition
Address Resolution Protocol - connects IP address to a MAC address to that devices can communicate on a LAN
94
TF: NAT is used to translate between private & public IP addresses
true
95
NAT definition
Network Address Translation - protocol that allows multiple devices on a private network to share a single public IP address
96
subnet definition
end systems logically grouped together by IP
97
TF: fiber optic cable has the lowest error rate & highest transmission speeds of all guided media
true
98
What devices make up the network core?
routers & switches
99
What application-layer protocol retrieves mail?
IMAP
100
TF: TCP is bidirectional and full duplex
true
101
HTML stands for
HyperText Markup Language
102
what kind of delay refers to the time it takes for a signal to travel from sender to recipient?
propagation delay
103
TF: Broadband, Wireless, and DSL are all internet connection technologies
true
104
TF: UDP is connectionless
true
105
purpose of the GET method in an HTTP request HTTP
requests a representation of the specified resource
106
what are the 2 types of HTTP messages?
request and response
107
HTTP's primary role in the Web
to define the structure of Web messages and how they are exchanged
108
In which layer of the OSI model does DNS primarily operate?
Application (layer 5)
109
TF: DNS is used for routing IP datagrams on the Internet
false
110
TF: SMTP is used for both sending and receiving email messages
false
111
What is the primary function of SMTP in the email communication process?
Transferring email messages between mail servers
112
Which port is typically used by SMTP for sending emails?
25
113
node definition
hosts & routers

IST220 (14 decks)

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