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CCNA - Network Vocab

4b/5b An encoding scheme 4B/5B uses 5-bit symbols and codes to represent 4 bits of data. 4B/5B is used in 100Base-tx ethernet.
ACK a 1-bit flag in the tcp header that indicates the acknowledgment field is valid.
acknowledgment a notification sent from one network device to another to confirm that some event has occured.
acknowledgment number a 32-bit field in the tcp segment header that specifies the sequence number of the next byte this host expects to receive as a part of the TCP session. It is used to recognize lost packets and flow control
address pool the range of ip addresses that can be assigned by the DHCP server.
Address resolution protocol the method of for finding a host's hardware address from its IPv4 network layer address.
administratively scoped address an IPv4 multicast address that is restricted to a local group or organization
AND one of the three basic binary logic operations. ANDing yields the following result: 1 and 1 = 1
argument additional data that is provided with a command to provide information used by the execution of the command. IOS command arguments are entered at the CLI after the command
ARP cache a logical storage in the host's RAM to store ARP entries
ARP poisoning a technique used to attack an ethernet network by sending fake ARP messages to an ethernet LAN. These frames contain false MAC addresses that confuse network devices
ARP table a logical storage in a host's RAM to store arp entries.
association identity AID a number used in the 802.11 header to specify the session between a wireless client and the access point.
asynchronous communication that does not use a common clock between the sender and receiver. To maintain timing
attenuation the loss of communication signal on the media. This loss is due to degradation of the energy wave over time.
authentication a process used to verify the identity of a person or process
authoritative a source of information that is highly reliable and known for its accuracy
backoff algorithm the retransmission delay used with CSMA/CD when a collision occurs. The algorithm forces each sender that detected the collisions to delay a random amount of time before attempting to retransmit.
bandwidth In networking
best effort network protocols or technologies that do not use the acknowledgment system to guarantee reliable delivery of information
binary a numbering system characterized by 1 and 0
bit binary digit used in the binary numbering system. Binary digits are units of information storage and communication in computing. Each bit can be either a 0 or a 1.
bit time the time required to send a single bit over some transmission medium. The time can be calculated at 1/speed
bridge a device that connects multiple network segments at the data link layer of the OSI model. Bridges were the predecessor to LAN switches.
bridge table the table used by a switch or bridge that associates MAC addresses with the outgoing port. The switch or bridge uses this table for its forwarding/filtering decisions.
bridging the process of forwarding frames in a switch or a bridge from one port to another port or from segment to segment
broadcast a form of transmission where one device transmits to all devices within the network or on another network
broadcast address an address used to represent a transmission from one device to all devices. In ethernet
broadcast domain a logical network composed of all the computers and networking devices that can be reached by sending a frame to the data link layer broadcast address.
burned in address the MAC address that is permanently assigned to a LAN interface or NIC. It is called burned-in because the address is burned into a chip on the card
cache a temporary storage where data that has been retrieved or calculated and is accessed frequently can be stored. After the data is stored in the cache
carrier a signal on a medium used to support the transmission of data. Data is carried over the medium by modulation.
carrier sense multiple access (CSMA) media access methodology in which a node wishing to transmit listens for a carrier wave before trying to send. If a carrier is sensed
carrier sense multiple access collision detect (CSMA/CD) The MAC algorithm used by ethernet devices in a shared media. The protocol requires a node wishing to transmit to listen for a carrier signal before trying to send. If a carrier is sensed
channel a communication path over a medium used to transport information from a sender to a receiver. Multiple channels can be multiplexed over a single cable
channel service unit/data service unit a device that connects to a local digital telephone loop for a WAN circuit to a serial interface on a network device
classful addressing a unicast IP address that is considered to have three parts: a network part
classless addressing an IPV4 addressing scheme that uses a subnet mask that does not follow classful addressing limitations. It provides increased flexibility when dividing ranges of IP addresses into separate networks. Classless addressing is considered the best in current n
client a network device that accesses a service on another computer remotely by accessing the network.
cloud In networking
code gropu a grouping of code that meets a certain
collaborative Information systems that allow the creation of a document or documents that can be edited by more than one person in real time
collision In ethernet
collision domain a physical or a logical area in a LAN where the signals sent by the interfaces ma be subject o being combined. Within a collision domain
connection oriented communication where the sender and receiver must prearrange for communications to occur; otherwise
connectionless any communication in which the sender and receiver do not prearrange for communications to occur
console port a port on cisco devices to which a terminal or computer with a terminal emulator is connected to the network device in order to communicate and configure the network device
control data data that directs a process. a flag in a data-link frame is an example of control data.
convergence another form of the root word converge in the phrase converged network. This kind of network aggregates various forms of traffic such as voice
cyclic redundancy check a type of hash function that is used to produce a small
daemon a computer program that runs in the background and is usually initiated as a process. Daemons often support server processes.
data communications equipment the devices and connections of a communications network that comprise the network end of the user to network interface. The DCE provides a physical connection to the network
data termianl equipment devices at the user end of a user-network interface that serves as a data source
decapsulation a process by which an end device
default gateway a device on a network that serves as an access point to other networks. A default gateway is used by a host to forward IP packets that have destination addresses outside the local subnet. A router interface typically is used as the default gateway. When t
default route Routing table entry that is used to direct frames for which a next hop is not explicitly listed in the routing table. This route is used to forward a packet when no other known route exists for a give packet's destination address.
delimiter this field of a frame signals the beginning or end of a frame.
destination IP address the layer 3 address to which the data is going.
deterministic refers to whether the performance of a device
digital logic also known as boolean algebra. These consist of the AND OR and IF operations
directed broadcast a term that describes IPv4 packets sent to all hosts in a particular network. In a directed broadcast
directly connected network a network that is connected to a device's interface. For example networks that interface with the router are known to be directly connected. Devices learn their initial IP routes based on being connected to these subnets.
dispersion the spreading of light signal caused by light signals traveling at different speeds through a fiber.
distributed a method of computer processing in which different parts of a program run simultaneously on two or more computers that are communicating with each other over a network
dns resolver the client part of the DNS client server mechanism. A DNS resolver creates queries sent a across a network to a same server
domain name a name
domain name system an internet wide system by which a hierarchical set of DNS servers collectively hold all the name IP address mappings
dotted decimal a convention for writing IP addresses with four decimal numbers
download to transfer data from the computer functioning as a server to the client computer you are using.
dynamic host configuration protocol a protocol used to dynamically assign IP configurations to hosts. The services defined by the protocol are used to request and assign an IP address
dynamic or private ports TCP or UDP ports that range from 49152 to 65535 and are not used by any defined server applications.
dynamic routing routing that adjusts automatically to network topology or traffic changes.
electromagnetic interface interface by magnetic signals caused by the flow of electricity. EMI can cause reduced data integrity and increased error rates on transmission channels. The physics of this process are that electrical current creates magnetic fields
enable password unencrypted password used to allow access to privledge EXEC mode from IOS user EXEC mode.
encapsulation the process by which a device adds networking heads and trailers to data from an application for the eventual transmission of the data onto a transmission medium.
encode to change the energy levels transmitted over some networking medium to transmit bits over that medium.
encryption the process of obscuring information to make it unreadable without special knowledge
end device a device such as a desktop or mobile device that is used by an end user.
ethernet PHY the physical interface transceivers. It deals with Layer 1 (the physical layer
extended star a network topology characterized by a central location connected to multiple hubs. In an extended star
extranet part of a company's intranet that is extended to users outside the company
fast ethernet a common name for ethernet technology that operates at 100 mbps.
fault tolerance the design on networks that can continue to operate without interruption in the case of hardware
fiber-optic cable physical medium that uses glass or plastic threads to transmit data. A fiber-optic cable consists of a bundle of these threads
fiber optics the glass fibers inside certain cables over which light is transmitted to encode 0 and 1
filtering in ethernet
FIN a 1-bit field in the TCP header that is used by a device that wants to terminate its session with the other device. This is done by inserting the FIN flag in the flag field found in the TCP segment
firewall any combination of hardware device and/or software application designed to protect network devices from outside network users and/or malicious applications and files.
flash a removable component that has memory space for storage. Used on the router or switch for storing the compressed operating system image.
flooding a process used by a switch or bridge to forward broadcasts and unknown destination unicasts. The bridge/switch forwards these frames out all ports except the port on which the frame was received.
flow control the management of data flow between devices in a network. It is used to avoid too much data arriving before a device can handle it
forwarding In ethernet
fragmentation the dividing of IP datagrams to meet the MTU requirement of a layer 2 protocol.
frame the layer 2 pdu that has been encoded by a data link layer protocol for digital transmission. Some different kinds of frames are ethernet frames and PPP frames.
full duplex communication that allows receipt and transmission simultaneously. A station can transmit and receive at the same time. There are no collisions with full-duplex ethernet transmision.
gateway normally
gigabit ethernet ethernet that transmits data at 1
global configuration mod from the priviledged mode
globally scoped addresses unique addresses that are public domain addresses.
goodput application-level throughput. It is the number of useful bits per unit of time from a certain source address to a certain destination
half duplex communication that only allows one station to receive while the other station is transmitting
hierarchical addressing an addressing scheme in which a network is partitioned into sections
high-order bit the portion of a binary number that carries the most weight
hop the passage of a data packet between two network nodes.
host a network device that has an IPv4 address assigned to it to communication over a network.
host address IPv4 address of a network host. When talking about host addresses
host group a group defined by a class D address (multicast
hub In ethernet
hybrid fiber-coax a network that incorporates both optical fiber along with coaxial cable to create a broadband network. commonly used by cable tv companies.
hypertext transfer protocol defines the commands
instant messaging real-time communication between two or more people through text. The text is conveyed through computers connected over a network such as the internet. files can also be transferred through the IM program to share files.
Institute of Electrical and Electronics Engineers An international
interframe spacing a time period between ethernet frames that allows fairness with the CSMA/CD algorithm. Without a space between frames in other words
intermediary device a device that connects end devices to the network or interconnects different networks. A router is an example of an intermediary device.
International Organization for Standardization An international standards body that defines many networking standards. Also
Internet The network that combines enterprise networks
Internet Assigned Numbers Authority An organization that assigns the numbers important to the proper operation of the TCP/IP protocol and the Internet
Internet backbone a high-speed line or series of connections that forms a major pathway within a network. The term is often used to describe the main network connections comprising the Internet.
Internet control message protocol As part of the TCP/IP internet layer
Internet Engineering Task Force The standards body responsible for the development and approval of TCP/IP standards
Internet service provider A company that helps create the Internet by providing connectivity to enterprises and individuals
internetwork a combination of many IP subnets and networks
Interpret as command In the telnet application
intranet a corporate system such as a website that is explicitly used by internal employees. Can be assessed internally or remotely
IP Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing
IP address a 32-bit number
IP header the header defined by the IP. Used to create IP packets by encapsulating data supplied by higher-layer protocol (such as TCP) behind an IP header.
jam signal in a shared media ethernet network
keyword Used in the CLI following the command. Keywords are parameters that are used with the command from a set of predefined values.
kilobits per second a unit of measurement of the number of times 1000 bits can be transmitted in 1 second. 1 kbps = 1000bps
latency the time that passes while some event occurs. In networking
layered model a model that consists of various layers that enable the development and explanation of technology to be done on a modular basis. This allows interoperability among different technologies among the different layers.
limited broadcast a broadcast that is sent to a specific network or series of networks.
limited scope address An IPv4 multicast address that is restricted to a local group or organization.
link-local address an IPv4 address in the range of to Communication using these addresses is used with a ttl of 1 and limited to the local network
local area network a network created for devices located in a limited geographic area
locally administered address a MAC address that can be configured on a device. The LAA can be used in place of the BIA . This means that you can replace a NIC or use a substitute device without changing the address used by the network to access the station.
Logical link control the IEEE 802.2 standard that defines the upper sublayer of the Ethernet Layer 2 specifications.
logical network a group of devices associated by the arrangement of a hierarchial addressing scheme. Devices in the same logical network that share a common network portion of their Layer 3 addresses.
logical topology a map of the devices on a network representing how the devices communcate with each other.
loopback a special reserved IPv4 address
low-order bit Represents the 0 in the binary number. In an IP subnet mask
MAC table on a switch
Mail user agent program used to download and send email. Email clients use POP3 to receive emails and use SMTP to send emails. Also called an email client
manchester encoding line code in which each bit of data is signified by at least one voltage level transition.
maximum transmission unit the largest IP packet size allowed to be sent out a particular interface. Ethernet interfaces default to an MTU of 1500 because the data field of an Ethernet frame should be limited to 1500 bytes
media access control the lower of the two sublayers of the IEEE standard for ethernet. It is also the name of that sublayer
media independent the networking layers whose processes are not affected by the media being used. In ethernet
media-dependent interface (MDI) The normal operation of ethernet ports on a hub. In this mode
media-dependent interface crossover MDIX is an alternative operation of ethernet ports on a hub. In this mode
metropolitan-area network a network with a geographic size between a LAN and a WAN. Typically used by service providers to create a highspeed network in a major metropolitan area where many customers might want high speed services between large sites around a city.
most significant bit the bit position in a binary number having the greatest value. The most significant bit is sometime referred to as the leftmost bit.
multicast client a member of a multicast group. Every multicast client in each group has the same IP address. Multicast addresses begin with 224.*.*.* and end with 239.*.*.*
multicast group a group that receives a multicast transmission. The members of a multicast group have the same mulitcast IP addressing to receive the same transmission.
multiplexing a process where multiple digital data streams are combined into one signal.
network 1.collection of computers
network address a dotted decimal number defined by the IPv4 protocol to represent a network or subnet. It represents the network that hosts reside in. Also called a network number or network ID.
Network address translation (NAT) translation RFC 1918 addresses to public domain addresses. Because RFC 1918 addresses are not routerd on the Internet
network baseline a collection of data that establishes a reference for network performance and behavior over a period of time. This reference data is used in the future to assess the health and relative growth of network utilization.
network interface card computer hardware
network segment a part of a computer network that every device communicates with using the same physical medium. Network segments are extended by hubs or repeaters.
Network time protocol a protocol for synchronizing the clocks of computer systems over packet-switch data networks. NTP uses UDP port 123 as its transport layer.
node data link layer term describing a device connected to a network.
noise In networking
nonreturn to zero line code in which 1s are represented by one significant condition and 0s are represented by another.
nonvolatile RAM (NVRAM) random-access memory that does not lose its contents when the computer is shut down
nslookup a service or a program to look up information in the DNS
octet a group of 8 binary bits. It is similar to
Open systems interconnection International standardization program created by ISO and ITU-T to develop standards for data networking that facilitate multivendor equipment interoperability
Optical time domain reflectometer a popular certification method for fiber systems. The OTDR injects light into the fiber and then graphically displays the results of the detected reflected light. The OTDR measures the elapsed transit time of reflected light to calculate the distance to d
Organizational Unique Identifier The first half of a MAC address. Manufactures must ensure that the value of the OUI has been registered with the IEEE. This value identifies the manufacturer of any Ethernet NIC or interface.
overhead resources used to manage or operate the network. Overhead consumes bandwidth and reduces the amount of application data that can be transported across the network.
packet when used generically
Packet Tracer a drag-and-drop network simulator developed by Cisco to design
Pad a part of the ethernet frame that fills in the data field to ensure that the data field meets the minimum size requirement of 46 bytes.
peer a host or node that participates in some form of a group. For example
physical address a data link layer address
physical media the cabling and connectors used to interconnect the network devices.
physical network the connection of devices on a common media. Sometimes a physical network is also referred to as a network segment.
physical topology the arrangement of the nodes in a network and the physical connections between them. This is the representation of how the media is used to connect the devices.
ping sweep a network scanning technique used to identify which host IP addresses are operational.
pinout defines which wires in a cable should connect to each pin on the connectors on both ends of a cable. For example
plug-in In a web browser
port In networking
positional notation somtimes called place-value notation
post office protocol a protocol that allows a computer to retrieve email from a server.
prefix length in IP subnetting
priority queing a routing feature in which frames in an interface output queue are prioritized based on various characteristics such as packet size and interface type.
prviate address define in RFC 1918
protocol a written specification that defines what tasks a service or device should perform. Each protocol defines messages
protocol data unit a generic term from OSI that refers to the data
protocol suite a delineation of networking protocols and standards into different categories
proxy arp a process that uses the same ARP messages as a normal ARP
PSH a 1-bit flag in the TCP header that is used to request to the higher layers for immediate delivery of the packet.
public address an IP address that has been registered with IANA or one of its member agencies
pulse amplitude modulation a form of signal modulation where the message information is encoded in the amplitude of series of signal pulses. It transmits data by varying the aplitunes of the individual pulses. This is now obsolete and has been replaced by pulse code modulation
quality of service a control mechanism that can provide different priorities to different users or data flows
query a request for information. Queries are answered with replies.
radio frequency interference radio frequencies that creat noise that interferes with information being transmitted across unshielded copper cabling.
radix the number of various unique digits
redundancy a network architecture designed to eliminate network downtime cause by a single point of failure.
Regional Internet Registries organizations that are responsible for the allocation and registration of Internet number resources within a particular region of the world. These registries include the American Registry for Internet Number for North America; RIPE network coordination ce
registered ports using values between 1024 and 49
Requests for Comments a series of documents and memoranda encompassing new research
reserved link-local addresses the IPv4 multicast addresses to These addresses are to be used for multicast groups on a local network. Packets to these destinations are always transmitted with a TTTL value of 1
resource records DNS data records. Their precise format is defined in RFC 1035. The most important fields in a resource record are Name
RJ-45 a rectangular cabling connector with eight pins
round-trip time the time required for some network pdu's to be sent and received
router path through an internetwork through which packets are forwarded.
router a network device
routing the process by which a router receives an incoming frame
router protocol a protocol used between routers so that they can learn routes to add to their routing tables.
routing table a list of router holds in memory for the purpose of deciding how to forward packets.
RST a 1-bit flag in the TCP header that is used to request that a connection be re-established.
runt frame an ethernet frame that is less than 64 bytes in size. Runts are caused by collisions and are also know as collision fragments
scalability the ability of a protocol. system or component to be modified to fit a new need.
scheme a plan
scope the extent of a certain item. For example
segment 1. a collision domain that is a section of a LAN that is bound by bridges
segmentation In TCP
selective forwarding the forwarding of packets where the forwarding decision is taken dynamically
server can refer to computer hardware that is to be used by multiple concurrent users. Alternatively
server message block an application level network protocl mainly applied to shared access to files
session a related set of communications transactions between two or more network devices.
shielded twisted pair cable a type of network cabling that includes twisted-pair wires
signal the optical or electrical impulse on a physical medium for purposes of communication.
smtp an application protocol typically not used by end users. Instead
single point of failure a system of network design characterized by one or more major components that are required to maintain operation.
slash format a method of expressing a network prefix. It uses a forward slash / followed by the network prefix.
slot time the minimum time a NIC or interface can take to send an entire frame. Slot time
source the origin of the PDU. This can be a process a host or a node
source IP address the IP address of the originating host that is placed into the IP packet header.
standards an internationally recognized definition of technical specifications that ensure worldwide consistency.
static route an entry in an IP routing table that was created because a network engineer entered the routing information into the router's configuration.
store and forward a method of internal processing by LAN switches. The switch must receive the entire frame before it sends the first bit of the frame. Store and forward switch is the method used by cisco switches.
subnet a group of IP addresses that have the same value in the first part of the IP addresses
subnet mask a dotted decimal number that helps identify the structure of IP addresses. The mask represents the network and subnet parts of related IP addresses with binary 1s and the host part of related IP addresses with binary 0s
switch In ethernet a layer 2 device that receives an electrical signal in one port
switch table the table used by a switch that associates MAC addresses with the outgoing port. A general term for the table that a LAN bridge uses for its forwarding/filtering decisions. The table holds a list of MAC addresses and the port out which the bridge should f
symmetric switching In LAN switches a reference to cases in which a frame is forwarded
SYN a 1-bt flag in the TCP header used to indicate the initial value of the sequence number. The SYN flag is only set in the first two segments of the three-way TCP connection establishment sequence.
synchronous Communication that uses a common clocking signal. In most synchronous communicatino
syntax the structure and order of words in a computer language
TCP a layer 4 protocl of TCP/IP model
TCP/IP a network model defined by the IETF that has been implemented on most computers and network device in the world.
test-net address the IPv4 address block to that is set aside for teaching and learning purposes. These addresses can be used in documentation and network examples.
Thicknet a common term for 10base5 ethernet
thinnet a common term for 10base2 ethernet
throuhpu the actual data transfer rate between two computers at some point in time. Throughput is impacted by the slowest-speed link used to send data between the two computers
Time to live a field in the IP header that prevents a packet form indefinitely looping around an IP internetwork. Router decrements the TTL field each time they forward a packet
token passing an access method used with some LAN technologies by which devices access the media in a controlled manner. This access to the LAN is managed using a small frame called a toke. A device can send only when it has claimed the use of the token.
tracert a command on many computer operating systems that discovers the IP addresses
transparent bridging the learning of source addresses on incoming frames and adding them to the bridging table. After the table has been completed and when a frame is received on one of the bridge's interfaces
unshieled twisted-pair a general type of cable
URG a 1-bit flag in the TCP header used to indicate that the receiving host should notify the destination process to do urgent processing.
user executive mode the limited CLI mode where the commands available to the user are a subset of those available at the privileged level. In general
virtual circuit a logical connection between devices in which the frames are passed between the devices. Virtual circuits are independent of the physical structure and may be established through multiple physical devices.
virtual local area network a network of computers that behave as if they are connected to the same network segment
virtual terminal line the reference to text based logical interfaces on an ios device. These are accesses using telnet or ssh to perform administrative tasks. VTY lines are also called virtual type terminal.
well known ports used by tcp or udp
window size as filed in the TCP header that is set in a sent segment
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