Google IT Support course glossary
A
A record: The most common resource record, used to
point a certain domain name at a certain IPv4 IP address
ACK flag: One of the TCP control flags. ACK is
short for acknowledge. A value of one in this field means that the
acknowledgment number field should be examined
Acknowledgement number: The number of the next expected segment
in a TCP sequence
Ad-Hoc network: A network configuration without
supporting network infrastructure. Every device involved with the ad-hoc
network communicates with every other device within range, and all nodes help
pass along messages
Address class system: A system which defines how the global IP
address space is split up
Address Resolution Protocol (ARP): A
protocol used to discover the hardware address of a node with a certain IP
address
Anycast: A technique that's used to route traffic
to different destinations depending on factors like location, congestion, or
link health
Application layer: The layer that allows network
applications to communicate in a way they understand
Application layer payload: The entire contents of whatever data
applications want to send to each other
ARP table: A list of IP addresses and the MAC
addresses associated with them
ASN: Autonomous System Number is a number
assigned to an individual autonomous system
Asymmetric Digital Subscriber Line (ADSL): A device that establishes data connections
across phone lines and different speeds for uploading and downloading data
Automatic allocation: A range of IP addresses is set aside for
assignment purposes
B
Baud rate: A measurement of how many bits could be
passed across a phone line in a second
Bit: The smallest representation of
data that a computer can understand
Bluetooth: The
most common short range wireless network
Border Gateway Protocol (BGP):
A protocol by which routers
share data with each other
Broadband: Any connectivity technology that isn't
dial-up Internet
Broadcast:
A type of Ethernet
transmission, sent to every single device on a LAN
Broadcast address: A special destination used by an
Ethernet broadcast composed by all Fs
C
Cable
categories: Groups of cables that are made with the
same material. Most network cables
used today can be split into two categories, copper and fiber
Cable
modem termination system: Connects lots of different cable
connections
to an ISP's core network
Cable
modem: A device that sits at the edge of a consumer's network and
connects it to the cable modem termination system
Cables:
Insulated wires that connect different devices to each other allowing
data to be transmitted over them
Caching
and recursive name servers: They are generally provided by an ISP or
your local network, and their purpose is to store domain name lookups for a
certain amount of time
Carrier-Sense
Multiple Access with Collision Detection (CSMA/CD):
CSMA/CD is used to determine when the communications channels are clear and
when the device is free to transmit data
Channels:
Individual, smaller sections of the overall frequency band used by a
wireless network
Client:
A device that receives data from a server
CLOSE: A
connection state that indicates that the connection has been fully terminated,
and that no further communication is possible
CLOSE_WAIT: A
connection state that indicates that the connection has been closed at the TCP
layer, but that the application that opened the socket hasn't released its hold
on the socket yet
Cloud
computing: The concept and technological approach of
accessing data, using applications, storing files, etc. from anywhere in the
world as long as you have an internet connection
CNAME: A
resource record used to map one domain to another
Collision
domain: A network segment where only one device can communicate at a time
Computer
networking: The full scope of how computers
communicate with each other
Connection-oriented
protocol: A data-transmission protocol that establishes a connection at the
transport layer, and uses this to ensure that all data has been properly
transmitted
Connectionless
protocol: A data-transmission protocol that allows data to be exchanged without
an established connection at the transport layer. The most common of these is
known as UDP, or User Datagram Protocol
Copper cable categories : These categories have different physical
characteristics like the number of twists in the pair of copper wires. These
are defined as names like category (or cat) 5, 5e, or 6, and how quickly data
can be sent across them and how resistant they are to outside interference are
all related to the way the twisted pairs inside are arranged
Crosstalk: Crosstalk is when an electrical pulse on
one wire is accidentally detected on another wire
Cyclical
Redundancy Check (CRC): A mathematical transformation that uses
polynomial division to create a number that represents a larger set of data. It
is an important concept for data integrity and is used all over computing, not
just network transmissions
D
Datalink layer: The layer in which the first protocols
are introduced. This layer is responsible for defining a common way of
interpreting signals, so network devices can communicate
Data offset field: The number of the next expected segment
in a TCP packet/datagram
Data packet: An all-encompassing term that represents
any single set of binary data being sent across a network link
Data payload section: Has all of the data of the protocols
further up the stack of a frame
Demarcate: To set the boundaries of something
Demarcation point: Where one network or system ends and
another one begins
Demultiplexing: Taking traffic that's all aimed at
the same node and delivering it to the proper receiving service
Destination MAC address: The hardware address of the intended
recipient that immediately follows the start frame delimiter
Destination network: The column in a routing table that
contains a row for each network that the router knows about
Destination port: The port of the service the TCP packet
is intended for
DHCP: A technology that assigns an IP address
automatically to a new device. It is an application layer protocol that
automates the configuration process of hosts on a network
DHCP discovery: The process by which a client configured
to use DHCP attempts to get network configuration information
Dial-up: Uses POTS for data transfer, and gets its
name because the connection is established by actually dialing a phone number
DNS zones: A portion of space in the Domain Name
System (DNS) that is controlled by an authoritative name server
Domain: Used to demarcate where control moves
from a top-level domain name server to an authoritative name server
Domain name: A
website name; the part of the URL following www.
Domain Name System (DNS): A global and highly distributed network
service that resolves strings of letters, such as a website name, into an IP
address
Dotted decimal notation: A format of using dots to separate
numbers in a string, such as in an IP address
DSL: Digital subscriber line was able to send
much more data across the wire than traditional dial-up technologies by
operating at a frequency range that didn't interfere with normal phone calls
DSLAM: Digital Subscriber Line Access
Multiplexers are devices that connect multiple DSL connections to a high-speed
digital communications channel
Duplex communication: A form of communication where
information can flow in both directions across a cable
Duration field: Specifies how long the total frame is
Dynamic allocation: A range of IP addresses is set aside for
client devices and one of these IPs is issued to these devices when they
request one
Dynamic IP address: An IP address assigned automatically to
a new device through a technology known as Dynamic Host Configuration Protocol
E
Error detection: The ability for a protocol or program to
determine that something went wrong
Error recovery: The ability for a protocol or program
to attempt to fix an error
ESTABLISHED: Status indicating that the TCP
connection is in working order, and both sides are free to send each other data
Ethernet: The protocol most widely used to send
data across individual links
Ethernet frame: A highly structured collection of
information presented in a specific order
EtherType field: It follows the Source MAC Address in a
dataframe. It's 16 bits long and used to describe the protocol of the contents
of the frame
Exterior gateway: Protocols that are used for the exchange
of information between independent autonomous systems
F
Fiber cable: Fiber optic cables contain individual
optical fibers which are tiny tubes made of glass about the width of a human
hair. Unlike copper, which uses electrical voltages, fiber cables use pulses of
light to represent the ones and zeros of the underlying data
FIN: One of the TCP control flags. FIN is
short for finish. When this flag is set to one, it means the transmitting
computer doesn't have any more data to send and the connection can be closed
FIN_WAIT: A TCP socket state indicating that a FIN
has been sent, but the corresponding ACK from the other end hasn't been
received yet
Firewall: It is a device that blocks or allows
traffic based on established rules
Five layer model: A model used to explain how network
devices communicate. This model has five layers that stack on top of each
other: Physical, Data Link, Network, Transport, and Application
Fixed allocation: Requires a manually specified list of
MAC address and the corresponding IPs
Flag field: It is used to indicate if a datagram is
allowed to be fragmented, or to indicate that the datagram has already been
fragmented
Flat file: A collection of records/information that
follow a consistent format with rules around stored values. On a host computer,
one use is to have a list of network address and host name pairs (a hosts file)
Flow
label field: 20-bit field that's used in conjunction
with the traffic class
field for routers to make decisions about the quality of service level
for
a specific datagram
Fragmentation:
The process of taking a single IP datagram and splitting it up into
several smaller datagrams
Fragmentation
offset field: It
contains values used by the receiving end to take all the parts of a
fragmented packet and put them back together in the correct order
Frame check sequence: It
is a 4-byte or 32-bit number that represents a checksum value for the
entire frame
Frame
control field: 16 bits long, it contains a number of
sub-fields that are used to
describe how the frame itself should be processed
Frequency band: A certain section of the radio spectrum
that's been agreed upon to be used for certain communications
FTP: An older method used for transferring
files from one computer to another, but you still see it in use today
FTTB: Fiber to the building, fiber to the
business or even fiber to the basement, since this is generally where cables to
buildings physically enter. FTTB is a setup where fiber technologies are used
for data delivery to an individual building
FTTH: Fiber to the home. This is used in
instances where fiber is actually run to each individual residents in a
neighborhood or apartment building
FTTN: Fiber to the neighborhood. This means
that fiber technologies are used to deliver data to a single physical cabinet
that serves a certain amount of the population
FTTP: Fiber to the premises. FTTH and FTTB may
both also be referred to as FTTP
FTTX: Stands for fiber to the X, where the X
can be one of many things
Full duplex: The capacity of devices on either side of
a networking link to communicate with each other at the exact same time
Fully qualified domain name: When you combine all the parts of a
domain together
H
Half-duplex: It means that, while communication is
possible in each direction, only one device can be communicating at a time
Handshake: A way for two devices to ensure that
they're speaking the same protocol and will be able to understand each other
HDSL: High Bit-rate Digital Subscriber Lines.
These are DSL technologies that provision speeds above 1.544 megabits per
second
Header checksum field: A checksum of the contents of the entire
IP datagram header
Header length field: A four bit field that declares how long
the entire header is. It is almost always 20 bytes in length when dealing with
IPv4
Hexadecimal: A way to represent numbers using a
numerical base of 16
Hop limit field: An 8-bit field that's identical in
purpose to the TTL field in an IPv4 header
Host file: It is a flat file that contains, on each
line, a network address followed by the host name it can be referred to as
Hub: It is a physical layer device that
broadcasts data to everything computer connected to it
Hybrid
cloud: Used to describe situations where companies might run things like
their most sensitive proprietary technologies on a private cloud or on
premise while entrusting their less sensitive servers to a public cloud
Hypervisor: A
piece of software that runs and manages virtual machines while also
offering guests a virtual operating
platform that's indistinguishable from actual hardware
I
IANA: The Internet Assigned Numbers Authority,
is a non-profit organization that helps manage things like IP address
allocation
ICMP: Internet
control message protocol is used by router or remote hosts to
communicate error messages when network problems prevent delivery of IP
packets
ICMP
payload: Piece of the packet which lets the recipient of the message knows which
of their transmissions caused the error being reported
Identification
field: It is a 16-bit number that's used to group messages together
Infrastructure
as a Service (IaaS): A subset of cloud computing where a
network and servers are provided for customers to run their services
Instantiation: The
actual implementation of something defined elsewhere
Interface: For a
router, the port where a router connects to a network. A router gives and
receives data through its interfaces. These are also used as part of the
routing table
Interior gateway: Interior gateway protocols are used by
routers to share information within a single autonomous system
Internet Protocol (IP): The most common protocol used in the
network layer
Internet Service Provider (ISP): A
company that provides a consumer an internet connection
Internetwork: A collection of networks connected
together through routers - the most famous of these being the Internet
IP datagram: a highly structured series of fields
that are strictly defined
IP masquerading: The
NAT obscures the sender's IP address from the receiver
IP options field: An optional field and is used to set
special characteristics for datagrams primarily used for testing purposes
IPv6 tunnel: IPv6 tunnel servers on either end of a
connection take incoming IPv6 traffic and encapsulate it within traditional
IPv4 datagrams
IPv6 tunnel brokers: Companies that provide IPv6 tunneling
endpoints for you, so you don't have to introduce additional equipment to your
network
L
Line coding: Modulation used for computer
networks
Link-local
unicast address: Allow for local network segment
communications and
are configured based upon a host's MAC address
Listen: It
means that a TCP socket is ready and listening for incoming connections
Local Area Network (LAN): A single network in which multiple
devices are connected
Loopback address: An IP address that always points to
itself. This type of address is used to test internal pathing through the
TCP/IP protocols
M
MAC(Media Access Control) address: A
globally unique identifier attached to an individual network interface. It's a
48-bit number normally represented by six groupings of two hexadecimal numbers
MAC filtering: Access points are configured to only
allow for connections from a specific set of MAC addresses belonging to devices
you trust
Mesh networks: Like ad-hoc networks, lots of devices
communicate with each other device, forming a mesh if you were to draw lines
for all the links between all the nodes
Metered connection: An internet connection where all data
transfer usage is tracked. Cell phone plans that have a limit on data usage per
month or that charge based on usage are examples of metered connections
Modulation: A way of varying the voltage of a
constant electrical charge moving across a standard copper network cable
Multicast: A way of addressing groups of hosts all
at once
Multicast frame: If the least significant bit in the
first octet of a destination address is set to one, it means you're dealing
with a multicast frame. A multicast frame is similarly set to all devices on
the local network signal, and it will be accepted or discarded by each device
depending on criteria aside from their own hardware MAC address
Multiplexing: It means that nodes on the network have
the ability to direct traffic toward many different receiving services
MX record: It stands for mail exchange and this
resource record is used in order to deliver email to the correct server
N
Name resolution: This process of using DNS to turn a
domain name into an IP address
Network Address Translation (NAT): A mitigation tool that lets organizations
use one public IP address and many private IP addresses within the network
Network layer: It's the layer that allows different
networks to communicate with each other through devices known as routers. It is
responsible for getting data delivered across a collection of networks
Network port: The physical connector to be able to
connect a device to the network. This may be attached directly to a device on a
computer network, or could also be located on a wall or on a patch panel
Network switch: It is a level 2 or data link device that
can connect to many devices so they can communicate. It can inspect the
contents of the Ethernet protocol data being sent around the network, determine
which system the data is intended for and then only send that data to that one
system
Next header field: Defines what kind of header is
immediately after this current one
Next hop: The IP address of the next router that
should receive data intended for the destination networking question or this
could just state the network is directly connected and that there aren't any
additional hops needed. Defined as part of the routing table
Node: Any device connected to a network. On
most networks, each node will typically act as a server or a client
Non-metered connection: A connection where your data usage is not
tracked or limited, instead you are charged a flat fee for unlimited and
unrestricted usage. A Wi-Fi connection is an example of a non-metered
connection
Non-routable address space: They are ranges of IPs set aside for use
by anyone that cannot be routed to
NS record: It indicates other name servers that may
also be responsible for a particular zone
NTP servers: Used to keep all computers on a network
synchronized in time
O
Octet: Any number that can be represented by 8
bits
Optical
Network Terminator: Converts data from protocols the fiber
network can
understand to those that are more traditional twisted pair copper
networks can understand
Options
field: It is sometimes used for more complicated flow control protocols
Organizationally Unique Identifier (OUI): The
first three octets of a MAC address
OSI model: A model used to define how network
devices communicate. This model has seven layers that stack on top of each
other: Physical, Data Link, Network, Transport, Session, Presentation, and
Application
P
Padding field: A series of zeros used to ensure the
header is the correct total size
Pairing: When a wireless peripheral connects to a
mobile device, and the two devices exchange information, sometimes including a
PIN or password, so that they can remember each other
Patch panel: A device containing many physical network
ports
Payload: The actual data being transported, which
is everything that isn't a header
Payload length field: 16-bit field that defines how long the
data payload section of the datagram is
Physical layer: It represents the physical devices that
interconnect computers
Platform as a service: A subset of cloud computing where a
platform is provided for customers to run their services
Point-To-Point VPN: Establishes a VPN tunnel between two
sites but VPN tunneling logic is handled by network devices at either side, so
that users don't all have to establish their own connections
Pointer resource record: It resolves an IP to a name
Port: It is a 16-bit number that's used to
direct traffic to specific services running on a networked computer
Port forwarding: A technique where specific destination
ports can be configured to always be delivered to specific nodes
Port preservation: A technique where the source port
chosen by a client, is the same port used by the router
Preamble: The first part of an Ethernet frame, it
is 8 bytes or 64 bits long and can itself be split into two sections
Presentation layer: It is responsible for making sure that
the unencapsulated application layer data is actually able to be understood by
the application in question
Private cloud: When a company owns
the services and the rest of the cloud infrastructure, whether on-site or in a
remote data center
Protocol: A defined set of standards that computers
must follow in order to communicate properly is called a protocol
Protocol field: A protocol field is an 8-bit field that
contains data about what transport layer protocol is being used
Proxy service: A server that acts on behalf of a client
in order to access another service
PSH flag: One of the TCP control flags. PSH is short
for push. This flag means that the transmitting device wants the receiving
device to push currently- buffered data to the application on the receiving end
as soon as possible
Public cloud: The cloud services provided by a third party
Public DNS servers: Name servers specifically set up so that
anyone can use them for free
Q
Quad A (AAAA) record: It is very similar to an A record except
that it returns in IPv6 address instead of an IPv4 address
R
Receiving address: The MAC address of the access point that
should receive the frame
Recursive name servers: Servers that perform full DNS resolution
requests
Registrar: An organization responsible for assigning
individual domain names to other organizations or individuals
Reverse lookup zone files: They let DNS resolvers ask for an IP, and
get the FQDN associated with it returned
Reverse proxy: A service that might appear to be a single
server to external clients, but actually represents many servers living behind
it
Round robin: It is a concept that involves iterating
over a list of items one by one in an orderly fashion
Router: A device that knows how to forward data
between independent networks
Routing protocols: Special protocols the routers use to speak
to each other in order to share what information they might have
RST flag: One of the TCP control flags. RST is short
for reset. This flag means that one of the sides in a TCP connection hasn't
been able to properly recover from a series of missing or malformed segments
S
Sequence control field: A field that is 16 bits long and mainly
contains a sequence number used to keep track of ordering the frames
Sequence number: A 32-bit number that's used to keep track
of where in a sequence of TCP segments this one is expected to be
Server: A device that provides data to another
device that is requesting that data, also known as a client
Server or Service: A program running on a computer waiting to
be asked for data
Service type field: A eight bit field that can be used to
specify details about quality of service or QoS technologies
Session layer: The network layer responsible for
facilitating the communication between actual applications and the transport
layer
Short-range wireless network: It is what mobile devices uses to connect
to their peripherals
Simplex communication: A form of data communication that only
goes in one direction across a cable
Socket: The instantiation of an endpoint in a
potential TCP connection
Software as a Service (SaaS):
A way of licensing the use of
software to others while keeping that software centrally hosted and managed
Source MAC address: The hardware address of the device that
sent the ethernet frame or data packet. In the data packet it follows the
destination MAC address
Source port: A high numbered port chosen from a special
section of ports known as ephemeral ports
SRV record: A service record used to define the
location of various specific services
Start Frame Delimiter (SFD): The last byte in the preamble, that signals
to a receiving device that the preamble is over and that the actual frame
contents will now follow
Start of authority: A declaration of the zone and the name of
the name server that is authoritative for it
Static IP address: An IP address that must be manually
configured on a node
Subnet mask: 32-bit numbers that are normally written as
four octets of decimal numbers
Subnetting: The process of taking a large network and
splitting it up into many individual smaller sub networks or subnets
Symmetric Digital Subscriber
Line (SDSL): A
device that establishes data connections across phone lines and has upload and
download speeds that are the same
SYN flag: One of the TCP flags. SYN stands for
synchronize. This flag is used when first establishing a TCP connection and
make sure the receiving end knows to examine the sequence number field
SYN_RECEIVED: A TCP socket state that means that a socket
previously in a listener state, has received a synchronization request and sent
a SYN_ACK back
SYN_SENT: A TCP
socket state that means
that a synchronization request has been sent, but the connection hasn't been
established yet
T
T-Carrier technologies: Technologies Invented to transmit multiple
phone calls over a single link. Eventually, they also became common
transmission systems to transfer data much faster than any dial-up connection
could handle
TCP checksum: A mechanism that makes sure that no data
is lost or corrupted during a transfer
TCP segment: A payload section of an IP datagram made up
of a TCP header and a data section
TCP window: The range of sequence numbers that might be
sent before an acknowledgement is required
Time-To-Live field (TTL): An 8-bit field that indicates how many
router hops a datagram can traverse before it's thrown away
Top Level Domain (TLD): The top level of the DNS or the last part
of a domain name. For example, the “com” in www.weather.com
Total hops: The total number of devices data passes
through to get from its source to its destination. Routers try to choose the
shortest path, so fewest hops possible. The routing table is used to keep track
of this
Total length field: A 16-bit field that indicates the total
length of the IP datagram it's attached to
Traffic class field: An 8-bit
field that defines the type of traffic contained within the IP datagram and
allows for different classes of traffic to receive different priorities
Transmission Control Protocol
(TCP): The data transfer protocol
most commonly used in the fourth layer. This protocol requires an established
connection between the client and server
Transmitter address: The MAC address of whatever has just
transmitted the frame
Transport layer: The network layer that sorts out which
client and server programs are supposed to get the data
TTL: The lifetime limit of data given in
seconds. This number can be configured by the owner of a domain name for how
long a name server is allowed to cache in entry before it should discard it and
perform a full resolution again
Twisted pair cable: The most common type of cabling used for
connecting computing devices. It features pairs of copper wires that are
twisted together
Two-factor authentication: A technique where more than just a username
and password are required to authenticate. Usually, a short-lived numerical
token is generated by the user through a specialized piece of hardware or
software
TXT record: It stands for text and was originally
intended to be used only for associating some descriptive text with a domain
name for human consumption
Types of DNS servers: There are five primary types of DNS
servers; caching name servers, recursive name servers, root name servers, TLD
name servers, and authoritative name servers
U
Unicast transmission: A unicast transmission is always meant for
just one receiving address
Urgent pointer field: A field used in conjunction with one of the
TCP control flags to point out particular segments that might be more important
than others
URG flag: One of the TCP control flags. URG is short
for urgent. A value of one here indicates that the segment is considered urgent
and that the urgent pointer field has more data about this
User Datagram Protocol (UDP): A transfer protocol that does not rely on
connections. This protocol does not support the concept of an acknowledgement.
With UDP, you just set a destination port and send the data packet
V
Version field: First field in an IP header that specifies
the version of IP
Virtual LAN (VLAN): It is a technique that lets you have
multiple logical LANs operating on the same physical equipment
Virtual Private Network
(VPN): A technology that allows for
the extension of a private or local network, to a host that might not work on
that same local network
Virtualization: A single physical machine called a host
runs many individual virtual instances called guests
VLAN header: A piece of data that indicates what the
frame itself is. In a data packet it is followed by the EtherType
W
Wide area network: Acts like a single network but spans across
multiple physical locations. WAN technologies usually require that you contract
a link across the Internet with your ISP
Wi-Fi Protected Access (WPA):
A security program that uses
a 128-bit key to protect wireless computer networks, which makes it more
difficult to crack than WEP
Wired Equivalence Privacy
(WEP): An encryption technology that
provides a very low level of privacy. WEP should really only be seen as being
as safe as sending unencrypted data over a wired connection
Wireless access point: A device that bridges the wireless and
wired portions of a network
Wireless LANS (WLANS): One or more access points act as a bridge
between a wireless and a wired network
Wireless networking: Networks you connect to through radios and
antennas
Z
Zone Files: Simple configuration files that declare all
resource records for a particular zone
