All Ch. Key Terms

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All Ch. Key Terms
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All Chapters Key Terms Network Fundamentals CCNA Exploration Companion Guide Cisco Networking Academy Mark Dye Rick Mcdonald Antoon Rufi
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All Chapters Key Terms, Network Fundamentals, CCNA Exploration Companion Guide, Cisco Networking Academy, Mark A. Dye, Rick Mcdonald, Antoon W. Rufi
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  1. Data Network
    A digital network used to send data between computers
  2. Network
    1. Collection of computers, printers, routers, switches and other devices that can communicate with each other over some transmission medium.

    2. Command that assigns a NIC-based address to which the router is directly connected.
  3. Internet
    The network that combines enterprise networks, individual users, and ISPs into a single global IP network.
  4. Download
    To transfer data from the computer functioning as a server to the client computer you are using
  5. Instant Messaging
    Real-time communication between two or more people through text.

    Ex: MSN, AIM, YahooMessanger....
  6. Real-time
    Events or signals that show output as fas as possible, or as they happen.
  7. blogs
    Website where entries are made in journal style, created by a user who is in control of the style , visitors may leave comments, aka: weblog.
  8. podcasts
    Digital media file(s) that are distributed over the Internet using syndication feeds, for playback on portable media players and PCs.
  9. wikis
    A website that lets visitors add, edit, and delete content typically anonymously.
  10. collaboration tool
    A tool that helps people communicate & collaborate

    • Examples:
    • Wikidocs, Google Docs, Microsoft Sharepoint....
  11. packet tracer
    A drag-and-drop network simulator developed by Cisco to design, configure, and troubleshoot network equipment within a controlled simulated program environment.
  12. intranet
    A corporate system such as a website that is explicitly used by internal employees. Can be accessed internally or remotely.
  13. extranet
    Part of a company's intranet that is extended to users outside the company (that is, normally over the Internet).
  14. wireless technology
    Allows communication without needing physical connectivity.

    Including cell phones, PDAs, wireless access points, wireless NICs
  15. standards
    An internationally recognized definition of technical specifications that ensure worldwide consistency.
  16. bits
    Binary digit used in the binary numbering system

    Digits are units of information storage and communication in computing.

    Each bit is either a 1 or 0
  17. binary
    A numbering system characterized by 1s & 0s
  18. source
    The origin of the PDU. This can be a process, a host, or a node, depending on the layer to which you are referring.
  19. router
    A network device, typically connected to a range of LAN & WAN interfaces, that forwards packets based on the destination IP addresses.
  20. cloud
    A network device that accesses a service on another computer remotely by accessing the network.
  21. IP
    Internet Protocol

    Network layer protocol in TCP/IP stack for a connectionless internetwork servic. Provides features for Addressing, type-of-service specification, fragmentation, reassembly and security.

    RFC 791
  22. TCP
    Transmission Control Protocol

    Layer 4 protocol of the TCP/IP model

    Lets applications guarantee delivery of data across a network.
  23. convergence
    A form of network that aggregates various forms of traffic such as voice, video and data on eeh same network infrastructure.

    &/OR

    Process by which routers recognize that something has occurred that changes some of the routers routes and reacts to the event to find another best route.
  24. fault tolerance
    The design on networks that can continue to operate without interruption in the case of hardware, software, or communication failures.
  25. redundancy
    A network architecture designed to eliminate network downtime caused by a single point of failure.
  26. scalability
    The ability of a protocol, system, or component to be modified to fit a new need.
  27. internetwork
    A combination of many IP subnets and networks, as created by building a network using routers.

    Used to avoid confusion with the term network since an internetwork can include several IP networks.
  28. packet
    [Generically]

    refers to end-user data along with networking headers and trailers that are transmitted through a network.

    [Specifically]

    Is end-user data, along with network or Internet layer headers and an higher layer headers, but no lower-layer headers or trailers.
  29. QoS
    Quality of Service

    Control mechanism that can provide different priorities to different users of data flows, or guarantee a certain level of performance to a data flow in accordance with requests from the application program.
  30. bandwidth
    Networking 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 (bps).
  31. priority queuing
    A routing feature in which frames in an interface output queue are prioritized based on various characteristics such as packet size and interface type.
  32. authentication
    A process used to verify the identity of a person or process.
  33. 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.
  34. single point of failure
    A system or network design characterized by one or more major components that are required to maintain operation.
  35. 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.
  36. segmentation
    TCP process of taking a large chunk of data and breaking it into small-enough pieces to fit within a TCP segment w/o breaking any rules about the max amount of data allowed in each segment.
  37. multiplexing
    Process where multiple digital data streams are combined into one signal.
  38. switch
    Ethernet Layer 2 device

    Requires electrical signal in one port, interprets the bits, and makes a filtering or forwarding decision about the frame.

    • Forwards a regenerated signal.
    • Has many ports (RJ-45)
  39. end device
    A device such as a desktop or mobile device that is used by an end user.
  40. host
    Network device that has an IPv4 address assigned to it to communicate over a network.
  41. client
    A network device that accesses a service on another computer remotely by accessing the network
  42. host address
    IPv4 address of a network host - Network Layer Address
  43. intermediary device
    Device that connects end devices to the network or interconnects different networks.

    Ex: Routers
  44. physical address
    Data link layer address

    Ex: MAC address.
  45. encoding
    To change energy levels transmitted over some networking medium to transmit bits over that medium.
  46. LAN
    Local-Area Network

    Network created for devices located in a limited geographic area, through which the company owning the LAN has the right to run cables.
  47. ISP
    Internet Service Provider

    Company that helps create the internet by providing connectivity to enterprises and individuals,

    as well as interconnecting to other ISPs to create connectivity to all other ISPs.
  48. protocols
    Written specification that defines what tasks a service or device should perform.

    Defines messages (headers), rules, process by which the messages are used to achieve some stated purpose.
  49. protocol suite
    Delineation of networking protocols and standards into different categories, called layers, along with definitions of which sets of standards and protocols need to be implemented to create products that can be used to create a working network.
  50. IEEE
    Institute of Electrical and Electronics Engineers

    International, nonprofit organization for the advancement of technology related to electricity.

    Maintains standards defining many LAN protocols.
  51. IETF
    Internet Engineering Task Force

    Standards body responsible for the development and approval of TCP/IP standards.
  52. layered models
    Model that consists of various layers that enable the development and explanation of technology to be done on a modular basis.

    Allows interoperability among different technologies among the different layers.
  53. TCP/IP
    Transmission Control Protocol/Internet Protocol

    Network model defined by the IETF that has been implemented on most computers and network devices in the world.
  54. encapsulation
    Process in which a device adds networking headers and trailers to data from an application for the eventual transmission of the data over the medium.
  55. decapsulation
    Process in which the end-device receives data from a transmission and examines the headers and trailers at each stack layer

    aka de-encapsulation
  56. PDU
    Protocol Data Unit

    Generic term from OSI that refers to the data, headers, and trailers about which a particular networking layer is concerned.
  57. segment
    1. Collision domain that is a section of a LAN that is bound by bridges, routers, or switches.

    2. LAN w/ bus topology it is a continuous electrical circuit that is often connected w/ repeaters.

    3. W/ TCP it serves as a verb referring to the work TCP does to accept a large piece of data from an end device breaking it into smaller pieces. OR as a noun it refers to one of those smaller pieces of data.
  58. frame
    Layer 2 PDU that has been encoded by a data link layer protocol for digital transmission.

    • Ex:
    • Ethernet frames
    • PPP frames
  59. OSI
    Open System Interconnection

    International standardization program created by ISO and ITU-T to develop standards for data networking that facilitate multivendor equipment interoperability.
  60. ISO
    International Organization for Standardization

    International standards body that defines many networking standards. Also, the standards body that created the OSI model.
  61. port
    multiple meanings in networking

    On a Ethernet hub, switch = interface (physical connector in the device you plug the cable into)
  62. data
    Application layer protocol data unit.
  63. source device
    The device that is originating the PDU.
  64. DNS
    Domain Name System

    Internet-wide system by which hierarchical set of DNS servers collectively hold all the name-IP address mappings, with DNS servers referring users tot he correct DNS server to successfully resolve a DNS name.
  65. RFC
    Requests for Comments

    Series of documents and memoranda encompassing new research, innovations, and methodologies applicable to Internet technologies.

    Reference for how technologies should work.
  66. syntax
    The structure and order of words in a computer language.
  67. session
    A related set of communications transactions between two or more network devices.
  68. client
    Network device that accesses a service on another computer remotely by accessing the network.
  69. server
    Can refer to computer hardware that is to be used by multiple concurrent users.

    Can refer to computer software that provides services to many users.

    Example: consists of web server software running on some computer.
  70. daemon
    Computer program that runs in the background and is usually initiated as a process.

    Ofter support server processes.
  71. peer
    A host or node that participates in some form of a group.

    Peers that participate jointly in the same activity, each having a server and client component.
  72. scheme
    A plan, design, or program of action to be followed.

    Sometimes an addressing plan is called an addressing scheme.
  73. IP Address
    32-bit number written in dotted decimal notation, used by the IP to uniquely identify an interface connected to an IP network.

    Also used as a destination address in an IP header to allow routing.

    Or as a source address to allow a computer to receive a packet and to know which IP address to send a response to.
  74. domain name
    Name defined by DNS that uniquely identifies a computer in the Internet.

    Corresponds with the IP address

    ex: www.cisco.com ip address
  75. network address
    A dotted decimal number defined by the IPv4 protocol to represent a network or subnet.

    REpresents the network that hosts reside in.

    AKA a network number or network ID
  76. resource record
    DNS data records.

    Precise format is defined in RFC 1035.

    Important fields: name, class, type, and data.
  77. DNS resolver
    Client end of the DNS client-server mechanism.

    Creates queries sent across a network to name a server, interprets responses, and returns information to the requesting programs.
  78. nslookup
    A part of a computer network that every device communicates with using the same physical medium.

    Can be extended by hubs or repeaters.
  79. query
    A request for information.

    Queries are answered with replies.
  80. cache
    Temporary storage where data that has been retrieved or calculated and is accessed frequently can be stored.

    Reduces the average access time and reduces the overhead of recalculating the data.
  81. authoritative
    A source of information that is highly reliable and known for its accuracy.
  82. plug-in
    In a web browser, an application the browser uses, inside the browser window, to display some types of content.

    Ex: typically uses a plug-in to display video.
  83. HTTP
    Hypertext Transfer Protocol

    Defines the commands, headers, and processes by which web servers and web browsers transfer files.
  84. distributed
    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.
  85. collaborative
    Information systems that allow the creation of a document(s) that can be edited by more than one person in real time.
  86. encryption
    Process of obscuring information to make it unreadable.

    Applies mathematical formula to the data along with a secret number (encryption key) resulting in an encrypted data packet and is sent through the network.
  87. POP
    Post Office Protocol

    A protocol that allows a computer to retrieve e-mail from a server.
  88. SMTP
    Simple Mail Transfer Protocol

    Application protocol typically not used by an end user.

    Used by the network management software and networking devices to allow a network engineer to monitor and trouble shoot network problems.
  89. MUA
    Mail User Agent Program

    Used to download and send e-mail.

    • Use POP3 to receive e-mails
    • Use SMTP to send e-mails
  90. spam
    Unsolicited commercial e-mail.
  91. gateway
    Relatively general term referring to different kinds of networking devices.

    {Routers were once galled gateways}
  92. DHCP
    Dynamic Host Configuration Protocol

    Used to dynamically assign IP config's to hosts.

    Services defined by the protocol are used to request & assign IP addresses, default gateway, and DNS server address to a network host.
  93. subnet mask
    A dotted decimal number that helps identify the structure of IP addresses.

    Mask represents the network and subnet parts of related IP addresses with binary 1s and the host part of related IP addresses with 0s.
  94. broadcast
    A form of transmission where one device transmits to all devices within the network or on another network.
  95. SMB
    Server Message Block

    An application level network protocol mainly applied to shared access to files, printers, serial ports, and miscellaneous communications between nodes on a network.
  96. UNIX
    A multiuser, multitasking operating system (196/70s)

    AT&T employees developed
  97. IAC
    Interpret as Command

    In Telnet application, commands are always interfaced by a character with the decimal code 255, known as an IAC character
  98. flow control
    The management of data flow between devices in a network.

    Used to avoid to much data arriving before a device can handle it, causing data overflow.
  99. control data
    Data that directs a process. A flag in a data-link frame is an example of control data.
  100. IANA
    Internet Assigned Numbers Authority

    An organization that assigns the numbers important to the proper operation of the TCP/IP protocol and the Internet, including assigning globally unique IP addresses.
  101. well-known ports
    • Used by TCP and UDP, with values between 0 - 1023
    • these ports are allocated by high-privilege processes.

    Used so that all clients know the correct port number to connect to.
  102. registered ports
    • Using values between 1024 - 49,151
    • these numbers are equivalent to well-known ports in concept,

    but they are specifically used for non-privileged application processes.
  103. dynamic or private ports
    TCP & UDP ports that range from 49152 - 65535 and are not used by any defined server applications.
  104. 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.
  105. ACK
    a 1-bit flag in the TCP header that indicates that acknowledgment field is valid.
  106. PSH
    a 1-bit flag in the TCP header that is used to request to the higher layers for immediate delivery of the packet.
  107. RST
    a 1-bit flag in the TCP header that is used to request that a connection be re-established.
  108. SYN
    a 1-bit flag in the TCP header used to indicate the initial value of the sequence number.

    Flag is only set in the first two segments of the three-way TCP connection establishment sequence.
  109. 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 done by inserting the FIN flag in the flag field found in the TCP segment.
  110. acknowledgment
    a notification sent from one network device to another to confirm that some event (like a receipt of a message) has occurred.
  111. window size
    As filed in the TCP header that is set in a sent segment, signifies the maximum amount of unacknowledged data the host is willing to receive before the other sending host must wait for an acknowledgment.

    Used for flow control.
  112. route
    Path through an internetwork through which packets are forwarded.
  113. source IP address
    The IP address of the originating-host that is placed into the IP packet header.
  114. IP header
    Header defined by the IP.

    Used to create IP packets by encapsulating data from higher layer protocols with an IP header.
  115. routing
    Process:

    1. router receives frame

    2. discards data-link header & trailer

    3. makes forwarding decision based on destination IP add.

    4. adds new data-link header & trailer based on outgoing interface

    5. forwards frame out the appropriate interface.
  116. hop
    The passage of a data packet between two network nodes (for example, between two routers).
  117. 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.
  118. connection oriented
    Communication where the sender and receiver must prearrange for communications to occure; otherwise, the communication fails.
  119. connectionless
    Any communication in which the sender and receiver do not prearrange for communications to occur.
  120. Destination IP address
    Layer 3 address to which the data is going.
  121. overhead
    Resources used to manage or operate the network.

    • Consumes bandwidth
    • Reduces the amount of data that can be transported across the network.
  122. best-effort
    Network protocols or technologies that do not use the acknowledgment system to guarantee reliable delivery of information.
  123. media independent
    Networking layers that are not affected by the media being used.

    In Ethernet these are all of the layers from the LLC sublayer of the Data Link layer and above.
  124. MTU
    Maximum Transmission Unit

    Largest IP packet size allowed to be sent out a particular interface.

    Ethernet defaults to 1500 because the data field is limited to 1500bytes [the IP packet sits within the Ethernet frames data field].
  125. fragmentation
    The dividing of IP datagrams to meet the MTU requirements of the Layer 2 protocol.
  126. TTL
    Time To Live

    Field in the IP header that prevents a packet from indefinitely looping around an IP internetwork.

    Routers decrease TTL field at each hop, once TTL=0 the packet is discarded.
  127. subnet aka subnetwork
    Group of IP addresses that have the same value in the first part of the IP address.

    For identifying a group by that part of the address.

    IP addresses with the same subnet are typically on the same network medium - not separated by routers.

    Short for subnetwork
  128. 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.
  129. hierarchical addressing
    Addressing scheme in which a network is partitioned into sections.

    Each section identifier forming one part of each destination's address and the destination identifier forming another.
  130. octets
    Group of 8 binary bits.

    Used to divide IPv4 addresses into four components.
  131. default gateway
    Device on a network that serves as an access point to other networks.

    Is used by a host to forward IP packets that have destination addresses outside the local subnet.
  132. routing table
    List that a router holds in memory for the purpose of deciding how to forward packets.
  133. default route
    Routing table entry that is used to direct frames for which a next hop is not explicitly listed in the routing table.

    Is used to forward a packet when no other known route exists for a given packet's destination address.
  134. static route
    Entry in an IP routing table that was created bc a network admin entered the routing config manually.
  135. dynamic routing
    Routing that adjusts automatically to network topology or traffic changes.
  136. routing protocols
    Protocol used between routers so they can learn routes to add to their routing tables.
  137. administratively scoped addresses
    IPv4 multicast address that is restricted to a local group or organization

    see also limited-scope address
  138. AND
    One of 3 basic binary logic operations.

    ANDing yields the following results:

    • 1 AND 1 = 1
    • 1 AND 0 = 0
    • 0 AND 1 = 0
    • 0 AND 0 = 0
  139. address pool
    Range of IP addresses that can be assigned by the DHCP server.
  140. broadcast address
    Address used to represent transmission from one device to all devices.

    • Ethernet the address = FFFF.FFFF.FFFF
    • is used to send the frame to all devices on the Ethernet LAN.

    IPv4 each subnet has a single broadcast address (aka subnet or directed broadcast address)
  141. classful addressing
    • Unicast IP address that is considered to have three parts:
    • 1. network part
    • 2. subnet part
    • 3. host part

    "glassful rules are first applied to the address and then the rest of the address is separated for subnetting"

    Class A, B, C, D & E
  142. classless addressing
    IPv4 address scheme using subnet masks that do not follow classful addressing limitations.

    Flexibility when dividing ranges of IP address into separate networks.

    Considered best for current networks.
  143. digital logic
    Consists of the AND, OR and IF operations

    aka Boolean algebra
  144. dotted decimal
    Convention for writing IP addresses with four decimal numbers that range from 0 - 255 (inclusive)

    Each octet (decimal number), 8-bits of the 32-bit address.

    Four octets are separated by a decimal.
  145. directed broadcast
    [Rather than being sent to all hosts in a particular network]

    A single copy of the packet is routed to the specific network it's destined for - where it is then broadcast to all hosts on that network.
  146. globally scoped address
    Unique addresses that are public domain addresses.
  147. high-order bits
    Portion of the binary number that carries the most weight.

    (the one written furthest to the left)

    Are the 1s in a network mask.
  148. Internet backbone
    High-speed line or series of connections that forms a major pathway within a net-work.

    Often used to describe the main network connections comprising the Internet.
  149. ICMP
    Internet Control Message Protocol

    Part of the TCP/IP Internet Layer.

    Defines protocol messages used to inform network admin how well the internetwork is operating.

    EX: ping command sends ICMP messages to verify that a host can send packets to another host.
  150. link-local addresses
    • IPv4 address in the range of:
    • 169.254.1.0 - 169.254.254.255

    Communication is limited to local network w/ TTL = 1
  151. loopback
    Reserved IPv4 address: 127.0.0.1

    Used to test TCP/IP applications (testing the stack)

    Does not require a working NIC as packet does not leave the computer.
  152. limited-scope addresses
    Multicast address that is restricted to a local group or organization.

    see also administratively scoped address
  153. limited broadcast
    Broadcast that is sent to a specific network or series of networks.
  154. low-order bits
    = host portion of the IP subnet mask.

    Represent the 0s in the binary number.
  155. most significant bit
    Bit position in a binary number having the greatest value.

    Typically the leftmost bit.
  156. multicast clients
    Member of a multicast group.

    Each client in group has same IP address.

    • Multicast addresses range:
    • 224.*.*.* - 239.*.*.*
  157. multicast group
    Group that receives multicast transmissions.

    All members have same IP address and receive all transmissions to that multicast address.
  158. NAT
    Network Address Translation

    Translation of RFC 1918 addresses to public domain addresses.

    (RFC 1918 addresses are not routable on the Internet)
  159. NTP
    Network Time Protocol

    For synchronizing the clocks of computers over packet-switched data networks.

    Uses UDP port 123 as it's transport layer.
  160. positional notation
    Numeral system in which each position is related to the next by a constant multiplier (common ratio that is the base of that numeral system)

    aka place-value notation
  161. prefix length
    (IP Subnetting)

    Refers to the portion of a set of IP addresses whose value must be identical for the addresses to be in the same subnet.
  162. public addresses
    IP address that has been registered with IANA or another agency.

    Ensures a globally unique public IP address that can be used to send packets through the Internet.
  163. private addresses
    Defined in RFC 1918

    IP address that is not globally unique bc the address exists inside packets only when the packets are inside a single private IP internetwork.

    Popular with companies who can then use NAT for a globally unique IP address.
  164. RTT
    Round-Trip Time

    Time between sending a PDU and receiving a response.

    The time for [some] PDUs to be sent and received & a response PDU sent and received.
  165. RIR
    Regional Internet Registries

    Organizations that are responsible for the allocation and registration of Internet number resources within a particular region of the world.

    • ARIN North America
    • RIPE Europe & Middle East
    • APNIC Asia & the Pacific
    • LACNIC South America
    • AfriNIC Africa
  166. reserved link-local addresses
    • IPv4 multicast addresses between:
    • 224.0.0.0 - 224.0.0.255

    Used for mulicast groups on a local network.

    Packet TTL always = 1
  167. radix
    Number of various unique digits - including 0

    radix aka base

    EX: binary system is base 2 (radix=2)
  168. scope
    Extent of a certain item from beginning to end

    Ex: address scope
  169. slash format
    Uses forward slash ( / ) to express the network prefix after the IP address.

    EX: 192.168.254.0/24

    Represents 24-bit network prefix
  170. test-net addresses
    • IPv4 address block:
    • 192.0.2.0 - 192.0.2.255 (192.0.2.0/24)

    Set aside for teaching and learning purposes.
  171. nodes
    Data Link layer term describing a device connected to a network.
  172. physical network
    Connection of devices on a common media.

    AKA network segment
  173. logical network
    Group of devices associated by the arrangement of a hierarchical addressing scheme.

    Devices share common network portion of their Layer 3 addresses.
  174. network segment
    Part of a computer network that every device communicates with using the same physical medium.

    Can be extended by hubs or repeaters.
  175. NIC
    Network Interface Card

    Computer Hardware - used for LANs

    Allows a computer to connect to a networking cable it can then send and receive data over the cable at the direction of the computer.
  176. LLC
    Logical Link Control

    IEEE 802.2 standard that defines the upper sublayer of the Ethernet Layer 2 specifications (and other LAN standards).
  177. MAC
    Media Access Control

    Lower of the two sublayers of the IEEE standard for Ethernet.

    Defined by 802.3
  178. deterministic
    Indicates whether the performance of a device, attached to a particular type of LAN can be accurately predicted (determined).

    EX: Token Ring, LANs
  179. CSMA
    Carrier Sense Multiple Access

    Media access method in which transmitting node listens for a signal on the media before transmitting.

    Will wait to transmit if a signal is detected.
  180. carrier
    Signal on a medium used to support the transmission of data.

    • Data is "carried" over the medium by modulation
    • (combining data signal w/ carrier signal)
  181. collision
    (Ethernet)

    Results of two nodes transmitting simultaneously.

    Causes damage to signals requiring them to be retransmitted.
  182. CSMA/CA
    Carrier Sense Multiple Access / Collision Avoid

    Mechanism used to regulate the transmission of data onto a network medium.

    Device requests right to send in order to avoid collisions.

    Used in 802.11 WLANs
  183. half duplex
    When communication can only be transmitted in one direction at one time.

    One station receives what the other transmits and must wait till completion to send the response.
  184. full duplex
    Communication that allows transmission and receipt at the same time.

    No collisions!
  185. physical topology
    Arrangement of the nodes in a network and the physical connections between them.

    Representation of how media is used to connect the devices.
  186. logical topology
    Map of the devices on a network representing how the devices communicate with each other.
  187. virtual circuit
    Logical connection between two devices in which the frames are passed between the devices.

    Independent of the physical structure and may be established through multiple physical devices.
  188. token passing
    Access method used with some LANs

    Devices access media in a controlled manner managed by a small frame called a token.

    Devices can only send when they have claimed the token.
  189. CRC
    Cycle Redundancy Check

    Type of hash function (one-way encryption) that is used to produce small, fixed-size checksum of a block of data, such as a packet or a computer file.

    CRC is computed & appended before transmission/storage and verified by the recipient to confirm nothing was changed during transmission.
  190. back-off
    Retransmission delay used with CSMA/CD when a collision occurs.

    Forces each sender that detected the collision to delay a random amount of time before attempting to retransmit.
  191. AID
    Association Identity

    Number used in the 802.11 header to specify the session between a wireless client and the access point.
  192. ARP
    Address Resolution Protocol

    Method for finding a host's hardware address (MAC) from its IPv4 Network Layer address.
  193. physical media (medium)
    Cabling & connectors used to interconnect the network devices.
  194. signal
    Optical or electrical impulse on a physical medium for purposes of communication.
  195. encode
    To change the energy levels transmitted over some networking medium to transmit bits over that medium.
  196. bit time
    Time required to send a single bit over some transmission medium.

    • Calculated as 1/speed
    • (Speed = number of bits per second sent over the medium)
  197. NRZ
    Non-Return to Zero

    Line code represented by one significant condition and 0s are represented by another.
  198. Manchester encoding
    Line code in which each bit of data is signified by at least one voltage level transition.
  199. code group
    Grouping of code that meets a certain specified condition for entering in that ceratin group.
  200. 4B/5B
    Encoding scheme

    Uses 5-bit symbols or codes to represent 4 bits of data

    Used in 100BASE-TX Ethernet
  201. kilobits
    kbps

    Unit of measurement of the number of times 1000 bits can be transmitted in 1 second.

    1kbps = 1000bps
  202. megabits
    Mbps

    Unit of measurement of the number of times 1,000,000 bits can be transmitted in 1 second.

    1 Mbps = 1,000,000 bps
  203. throughput
    Actual data transfer rate between two computers at some point in time.

    Impacted by the slowest-speed link used to send data between the two computers.

    (In addition to any other outside factors.)
  204. goodput
    Application-level throughput.

    Number of useful bits per unit of time from a certain source address to a certain destination.

    Excluding protocol overhead & retransmitted data packets.
  205. attenuation
    Loss of communication signal on the media.

    Due to degradation of the energy wave over time.
  206. noise
    General term referring to any energy signal on a transmission medium that is not part of the signal used to transmit data over that medium.
  207. UTP
    Unshielded Twisted-Pair cable

    General type of cable, cable holds twisted pairs of copper wires and the cable itself having little shielding.
  208. RJ-45
    A rectangular cabling connector with eight pins, often used with Ethernet cables.
  209. pinout
    Defines which wires in a cable should connect to each pin on the connectors on both ends of a cable.
  210. straight-through cable
    UtP cable pinout that specifies that the wire at pin 1 connects to pin 1 on the other end, pin 2 to pin 2, pin 3 to pin 3, etc.

    EX: connecting PC to hub or switch
  211. crossover cable
    UTP cable used in Ethernet

    Some pairs of twisted-pair wires are crossed at either ends of the RJ-45.
  212. rollover cable
    Cisco proprietary cable

    UTP pinout that specifies RJ-45 pinout connects pin 1 to pin 8, pin 2 to pin 7, pin 3 to pin 6, etc.

    Cisco console cables for routers and switches.
  213. coax / coaxial cable
    Cable.

    Consisting of a hollow outer cylindrical conductor that surrounds a single inner wire conductor.

    • Three different layers of material surrounding the inner conducting material:
    • the outer conductor
    • the insulator
    • the protective outer jacket
  214. HFC
    Hybrid Fiber-Coax

    Network that incorporates both optical fiber along with coaxial cable to create a broadband network.
  215. STP
    Shielded Twisted-Pair cable

    Type of network cable that includes twisted-pair wires, with shielding around each pair of wires,, as well as another shield around all wires in the cable.
  216. fiber-optic cable
    Physical medium that uses glass or plastic threads to transmit data.

    Transmit data via light waves.
  217. OTDR
    Certification method for fiber.

    Tool for testing fiber measuring the time to shine in one end and out the other noting the imperfections in between.
  218. asynchronous
    Communication that does not use a common clock between the sender and receiver.

    Additional info is sent to maintain timing, synch and receive circuit to the incoming data.

    10Mbps Ethernet device does not send sync signals.
  219. ARP table / cache
    Logical storage in host's RAM to store ARP entries.
  220. ARP spoofing / poisoning
    Technique to attack an Ethernet network by sending fake ARP messages to an Ethernet LAN.

    Frames contain false MAC addresses that "confuse" network devices (ex: switches).

    Causes frames intended for one node could be sent to another by mistake.
  221. bridge
    Device that connects multiple network segments at the data link layer of the OSI model.

    Predecessor to the LAN switch.
  222. bridge table
    Used by a switch or bridge that associates MAC addresses with the outgoing port.

    Uses table as reference for forwarding & filtering.
  223. bridging
    Process of forwarding frames in a switch or bridge from one port to another port from segment to segment.
  224. BIA
    Burned-In Address

    MAC address that is permanently assigned to a LAN interface or NIC.

    • Burned onto the chip on the card.
    • Can not be changed.

    aka UAA (Universally Administered Address)
  225. CSMA/CD
    Carrier Sense Multiple Access / Collision Detect

    MAC algorithm used by Ethernet devices in a shared media.

    Protocol requires a node listen for existing signal on the media before attempting to send its data.

    If signal is found the node waits until the media is clear before transmit.

    If collision occurs and/or is detected the sending node issues a back-off algorithm before retransmitting.
  226. collision domain
    Physical or logical area in a LAN where the signal sent by the interfaces may be subject collision.

    Every device in the same collision domain receives frames sent out by other devices on that same segment.

    • Hubs increase the size of the collision domain.
    • Switches separate them.
  227. delimiter
    Field of a frame signals the beginning or end of a frame.
  228. extended star
    Network topology characterized by a central location connected to multiple hubs.

    Hierarchical topology but typically drawn w/ central site in the center.

    aka hierarchical star
  229. Ethernet PHY
    Physical interface transceivers.

    Deals with Layer 1 of Ethernet.
  230. flooding
    Switch/bridge process to forward broadcasts & unknown destination unicasts out all ports except the one frame is received on.
  231. filtering
    Ethernet switch/bridge process that decides not to forward a frame out another port.
  232. forwarding
    Ethernet switch/bridge process that decides to forward a frame out another port.
  233. FastEthernet
    Common name for Ethernet technology that operates at 100 Mbps.
  234. Gigabit Ethernet
    Ethernet that transmits data at 1,000,000,000 (1billion) bits per second.
  235. host group
    Group defined by a class D address

    (multicast, ranging 224.0.0.0 - 239.255.255.255)

    Hosts can pertain to multicast groups.

    Groups = hosts with same multicast address
  236. hub
    Ethernet device that receives an electrical signal in one port -interprets the bits- regenerates the signal out all ports.

    • Several ports
    • Extends networks - collision domains
    • Repeaters
    • Usually RJ-45
  237. interframe spacing
    Time period between Ethernet frames that inserts a space between frames.

    {allows fairness with the CSMA/CD algorithm }
  238. jam signal
    A shared media Ethernet network signal generated when a collision is detected.

    Lasts long enough for all devices to receive.

    Part of CSMA/CD.
  239. LAA
    Locally Administered Address

    MAC address that can be configured on a device.

    Can be used in place of BIA.

    Allows NIC to be replaced or device substituted w/o changing the address used by the network to access the station.
  240. latency
    Time that passes while some event occurs.

    Refers to the time that occurs between when something is sent in a network until it is received by another device.
  241. MAC table
    Table on a switch that lists all known MAC addresses and the association port for forwarding frames.
  242. MAN
    Metropolitan-Area Network

    Networks geographic size - between LAN and WAN [in size].

    Used by ISPs to create high-speed networks in metropolitan areas.
  243. OUI
    Organizational Unique Identifier

    First half of MAC address.

    Manufacturers must register the value of the OUI with the IEEE.

    Identifies manufacturer of Ethernet NIC or interfaces.
  244. Pad
    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.
  245. proxy ARP
    Process that uses the same ARP messages as normal ARP however a router replies instead of the host listed in the request.

    Router acts on behalf of the host to respond to the ARP request with the router's MAC address listed in the ARP reply so that the device can reach the intended host that it otherwise would not be able to reach.
  246. PAM
    Pulse Amplitude Modulation

    Form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses.

    Transmits data by varying the amplitudes (voltage/power levels) of the individual pulses.

    Obsolete: replaced by PCM (Pulse Code Modulation)
  247. ROM
    Type of memory on which data has been prerecorded.

    Can not be removed - only read.
  248. RAM
    Main working area [temporary storage] used by the CPU for most processing and operations.

    Requires electrical power to maintain data storage. (Power turned off before saving - data is lost.)

    aka read-write memory
  249. runt frames
    Ethernet frame that is less than 64 bytes in size

    Caused by collisions

    • aka collision fragments
    • { minimum frame size = 64 bytes }
  250. selective forwarding
    Decisions to forward packets are made dynamically, hop by hop based on conditions on downstream nodes.
  251. store & forward
    Internal processing by LAN switches.

    Switch must receive the entire frame before it sends the first bit of the frame.

    (Cisco switches)
  252. switch table
    Associates MAC addresses with their corresponding port.

    see also bridge table.
  253. synchronous
    Communication that uses a common clocking signal.

    One of the communicating devices generates a clock signal into the circuit - additional timing info is not required in the header.
  254. slot time
    Minimum time a NIC or interface can take to send an entire frame.

    Slot time, then implies a minimum frame size.
  255. Thicknet
    Common term for 10BASE5 Ethernet.

    Thicker than 10BASE2 coax cable used for Thinnet.
  256. Thinnet
    Common term for 10BASE2 Ethernet.

    Thinner than 10BASE5 cable for Thicknet.
  257. transparent bridging
    Device learns source addresses of incoming frames and adds them to the bridging table (switch table, etc.)

    For forwarding frames received on one of the interfaces.
  258. UAA
    Universally Administered Address

    • aka
    • BIA - burned in Address
    • MAC Address
  259. VoIP
    Voice data encapsulated in an IP packet that allows it to traverse already implemented IP networks w/o needing its own network infrastructure.
  260. VLAN
    Network of computers that behave as if they are connected to the same network segment - even if they are located on different segments of a LAN.

    • Configured through software on the switch and router.
    • (IOS on Cisco routers/switches)
  261. console port
    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.
  262. CSU/DSU
    Channel Service Unit / Data Service Unit

    Device that connects a local digital phone loop for a WAN circuit to a serial interface on a network device (typically a router).

    Performs physical layer layer1 signaling on WAN circuits.
  263. DCE
    Data Communications Equipment

    Devices and connections of a communications network that comprise the network end of the user-to-network interface.

    • Physical connection to the network
    • Forwards traffic
    • Provides clocking signal used to synch data transmissions between DTE & DCE

    Ex: modems, Interface cards, etc...
  264. DTE
    Data Terminal Equipment

    Device the user end of a user-network interface serving as a data source, destination or both.

    Ex: computers, protocol translators, multiplexers, etc...

    Connects data network through a DCE device (modem) and uses clocking signals generated by DCE.
  265. EMI
    Electromagnetic Interference

    Interference by magnetic signals caused by the flow of electricity.

    Causes reduced data integrity and increased error rates on transmission channels.

    { The electrical current creates magnetic fields, which in turn cause other electrical current in nearby wires. Induced electrical currents can interfere with proper operation of the other wire. }
  266. fiber-optics
    Glass fibers inside certain cables over which light is transmitted to encode 1s & 0s.
  267. MDI
    Media-Dependent Interface

    Normal mode of operation of Ethernet ports on hubs .

    Mapping of the wire pairs used in the hub port is a normal config.
  268. MDIX
    Media-Dependent Interface, Crossover

    Alternative operation of Ethernet ports on a hub.

    Mapping of the wire pairs used on the hub port is a crossover config. that allows for the use of a straight-through cable. (interconnects a hub to a hub)
  269. RFI
    Radio Frequency Interference

    Radio frequencies that create noise that interfeares with information being transmitted across unshielded copper cabling (UTP).
  270. terminal emulator
    Application that runs a terminal for a remote host such as a router, switch, etc.
  271. Winchester connector
    34-pin female v.35 serial cable conector
  272. Command in EXEC mode:

    Enable
    enters privileged EXEC mode
  273. Command in Privileged EXEC mode:

    copy running-config running-config
    copy the active configuration to NVRAM
  274. Command in Privileged EXEC mode:

    copy startup-config running-config
    copy the configuration in NVRAM to RAM
  275. Command in Privileged EXEC mode:

    erase startup-configuration
    erase the configuration located in NVRAM
  276. Command in Privileged EXEC mode:

    ping ip_address
    ping to that address
  277. Command in Privileged EXEC mode:

    traceroute ip_address
    trace each hop to that address
  278. Command in Privileged EXEC mode:

    show interfaces
    display statistics for all interfaces on a device
  279. Command in Privileged EXEC mode:

    show clock
    show the time set in the router
  280. Command in Privileged EXEC mode:

    show version
    • Displays:
    • -currently loaded IOS version
    • -hardware
    • -device information
  281. Command in Privileged EXEC mode:

    show arp
    display the ARP table of the device
  282. Command in Privileged EXEC mode:

    show startup-config
    display the saved configuration located in NVRAM
  283. Command in Privileged EXEC mode:

    show running-config
    display the content of the currently running configuration file
  284. Command in Privileged EXEC mode:

    show ip interface
    display IP statistics for interface(s) on a router
  285. Command in Privileged EXEC mode:

    configure terminal
    enter terminal configuration mode
  286. Command in Terminal configuration mode:

    hostname hostname
    assigns host name to a device
  287. Command in Terminal configuration mode:

    enable password password
    set an unencrypted enable password
  288. Command in Terminal configuration mode:

    enable secret password
    set a strongly encrypted enable password
  289. Command in Terminal configuration mode:

    service password-encryption
    encrypt display of all passwords except secret
  290. Command in Terminal configuration mode:

    banner mode# message#
    set a message-of-the-day banner
  291. Command in Terminal configuration mode:

    line console 0
    enter console line configuration mode
  292. Command in Terminal configuration mode:

    line vty 04
    enter virtual terminal (Telnet) line configuration mode
  293. Command in Terminal configuration mode:

    interface interface_name
    enter interface configuration mode
  294. Line configuration mode:

    login
    enable password checking at login
  295. Line configuration mode:

    password password
    set line password
  296. Interface configuration mode:

    ip address ip_address netmasks
    set interface IP address and subnet mask
  297. Interface configuration mode:

    description description
    set interface description
  298. Interface configuration mode:

    clock rate value
    set clock rate for DCE device
  299. Interface configuration mode:

    no shutdown
    set interface to up
  300. Interface configuration mode:

    shutdown
    administratively set interface to down
  301. arguments
    Additional data provided by entering a command at the CLI then the argument.
  302. flash
    Removable component of memory storage space.

    Used on the router or switch for storing the compressed operating system image.
  303. global configuration mode
    From privileged mode,

    For configuring global parameters or enter other config submodes.
  304. keywords
    Follows a CLI command.

    Are parameters that are used with the command from a set of predefined values.
  305. network baseline
    Collection of data that establishes a reference for network performance and behavior over a period of time.

    Used in the future to assess the health and relative growth of network utilization.
  306. NVRAM
    Nonvolatile RAM (Random-access memory)

    Does not lose its contents when the computer is shut down.
  307. ping sweep
    Network scanning technique used to identify which host IP addresses are operational.
  308. SSH
    Secure Shell Protocol

    Provides a secure remote connection to a host through a TCP application.
  309. strong passwords
    Password that is complex and a minimum of 8 characters.

    Use both numbers and letters.
  310. user executive (EXEC) mode
    Limited CLI mode

    Can change terminal settings, perform basic tests & list system information.
  311. vty
    virtual terminal line

    Reference to text based logical interfaces on an IOS device.

    Accesses using Telnet or SSH to perform admin tasks.

    aka virtual type terminal

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