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, 1 and 0 = 0, 0 and 1 = 0

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, such as switches. As a result, frames intended for one node can be mistakenly sent to another node.

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, additional information is sent to synchronize the receive circuit to the incoming data. For ethernet at 10MBPS, the ethernet devices do not send electrical signals for synchronization

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, a measurement of the speed of bits that can be transmitted over a particular link. It is the amount of data that can be transmitted in a certain amount of time. For digital bandwidth it is usually expressed in bits per second.

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, where speed is the number of bits per second sent over the medium

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, the sepcial ethernet address FFFF.FFFF.FFFF is used as a destination MAC address to cause a frame to be sent to all devices on an ethernet LAN. In IPV4, each subnet has a single broadcast address, which is more commonly called the subnet or directed broadcast address.

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, and the address cannot be changed. Also called universally administered address.

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, the processes can access the cached copy instead of accessing the original data. A cache reduces the average access time and reduces the overhead of recalculating the data.

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, the node waits for the transmission in progress to finish before initiating its own transmission.

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, the node waits for transmission in progress to finish before initiating its own transmission. If a collision occurs and is detected, the sending node uses the backoff algorithm before retransmitting.

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, typically connecting to a router. The CSU/DSU performs physical Layer 1 signaling on WAN circuits

classful addressing

a unicast IP address that is considered to have three parts: a network part, a subnet part, and a host part. The term classful refers to the fact that classful network rules are first applied to the address, and then the rest of the address can be separated into a subnet and a host part to perform subnetting. In the early days of IPV4, IP addresses were divided into five classes, namely A, B, C, D and E.

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 network implementations.

client

a network device that accesses a service on another computer remotely by accessing the network.

cloud

In networking, a symbol used when drawing network diagrams that represent a part of the network whose details can be ignored for the purposes of the diagram.

code gropu

a grouping of code that meets a certain, already specified, condition for entering in that certain group.

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, the results of two nodes transmitting simlutaneously. The signals from each device are damaged when they combine on the media

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, if a device sends a frame on a network segment, every other device on that same segment will receive that frame. In an ethernet network, repeaters and hubs increase the size of collision domains by propagating the signals. LAN switches and bridges separate collision domains.

connection oriented

communication where the sender and receiver must prearrange for communications to occur; otherwise, the communication fails.

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, video and data on the same network infrastructure. A more common usage represents the process by which routers recognize that something has occured that changes some routers' routes, reacts to the event and finds the now-currently best routes.

cyclic redundancy check

a type of hash function that is used to produce a small, fixed size checksum of a block of data, such as a packet or a computer file. A CRC is computed and appended before transmission or storage, and verified afterward by the recipient to confirm that no changes have happened in transit.

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, forwards traffic, and provides a clocking signal used to synchronize data transmission between DCE and DTE devices. Modems and interface cards are examples of DCE. Compare to DTE

data termianl equipment

devices at the user end of a user-network interface that serves as a data source, destination or both. DTE connects to a data network through a DCE device and typically uses clocking signals generated by the DCE. DTE includes such devices as computers, protocols translators, and multiplexers.

decapsulation

a process by which an end device, after it receives data over some transmission medium, examines the headers and trailers at each successive higher layer, eventually handing the data to the correct application. Sometimes called de-encapsulation.

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 the computer needs to send a packet to another subnet, it sends the packet to its default gateway.

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, attached to a particular type of LAN, can be accurately predicted. Token Ring LANS are deterministic, but ethernet LANS are non deterministic.

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, a single copy of the packet is routed to the specified network, where it is broadcast to all hosts on that network

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, interprets responses, and returns information to the requesting programs.

domain name

a name, as defined by DNS that uniquely identifies a computer in the internet. DNS servers can then respond to the DNS requests by supplying the IP address that is used by the computer that has a particular domain name. This term also refers to the part of a URL that identifies a single company or organization, such as ciscopress.com

domain name system

an internet wide system by which a hierarchical set of DNS servers collectively hold all the name IP address mappings, with DNS servers referring users to the correct DNS server to successfully resolve a DNS name.

dotted decimal

a convention for writing IP addresses with four decimal numbers, ranging from 0 to 255, with each octet representing 8 bits of the 32 bit IP address. The term originates from the fact that each of the four decimal numbers is separated by a period.

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, default gateway, and DNS server address to a network host.

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, which in turn cause other eletrical currents in nearby wires. The included electrical currents can interfere with proper operation of the other wire.

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, somtimes referred to as scrambling. The process takes the data to be encrypted and applies a mathematical formula to it along with a secret number. The resulting value, which is called an encrypted packet is sent through a network

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, hence the PHY) of ethernet.

extended star

a network topology characterized by a central location connected to multiple hubs. In an extended star, these interconnected hubs may be connected to more hubs. It is essentially a hierarchical topology but typically is drawn with the central site in the center, with the rest of the topology radiating outward in all directions. This is sometimes called a hierarchical 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, software or communications failures.

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, each of which is capable of transmitting data into light waves.

fiber optics

the glass fibers inside certain cables over which light is transmitted to encode 0 and 1

filtering

in ethernet, the process performed by a bridge or switch when it decides that it should not forward a frame out another port

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, causing data overflow.

forwarding

In ethernet, the process performed by a bridge or switch when it decides that it should send a frame out another port.

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, a relatively general term that refers to dfifferent kinds of networking devices. Historically, when routers were created, they were called gateways

gigabit ethernet

ethernet that transmits data at 1,000,000,000 one billion bits per second.

global configuration mod

from the priviledged mode, you can enter the device's global caonfiguration mode. From global configuration mode, you can configure global parameters or enter other configuration submodes such as interface, router and line configuration submodes.

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, excluding protocol overhead and excluding retransmitted data packets.