Key Terms

CH1:

Ø  ASCII (American Standard Code for Information Interchange) A standardized method for formatting binary information and text for communications and printer control. The acronym ASCII is pronounced “ask-ee.”

Ø  Application layer The seventh layer of the OSI model, which is responsible for requesting network services and for providing services to applications.

Ø  BMP A Windows Bitmap (BMP) file, a graphical image type used with Microsoft Windows applications.

Ø  Burned in Address (BIA) The MAC address that is permanently added to the network card during the manufacturing process.

Ø  Carrier Sense Multiple Access with Collision Detection (CSMA/CD) The network access method used by Ethernet networks.

Ø  client A computer that operates on a network and requests and uses the services of other computers on the network, but does not necessarily provide any services to other computers.

Ø  client/server A type of networking in which a few dedicated computers, called servers, share files, printers, disk drives, and other resources with a group of client computers.

Ø  connection-oriented Network communications that require acknowledgment. On the OSI reference model, the decision to use connection-oriented communications is made at the Transport layer.

Ø  connectionless Network communications that do not require acknowledgment. On the OSI reference model, the decision to use connectionless communications is made at the Transport layer.

Ø  cyclic redundancy check (CRC) The process that ensures that data was not corrupted during transmission. This is accomplished by comparing CRC calculations before and after transmission.

Ø  Data Link layer The second layer of the OSI protocol stack, which defines the rules for sending and receiving information across the network media. It encodes and frames data for transmission and provides error detection and control. This layer has two parts: LLC and MAC.

Ø  datagram A message or packet that is sent across a network and does not require acknowledgment by the destination station.

Ø  electromagnetic interference (EMI) Electronic noise that disrupts signals on cables. This noise is frequently caused by motors and generators, but can also be caused by sunspots and other natural EMI-producing phenomena.

Ø  encapsulation A process that occurs during transmission through the protocol stack, in which data from the higher layers is wrapped in a protocol header and/or trailer.

Ø  end system The location and/or set of controls that the user can manipulate to interact with a computer or a network.

Ø  Ethernet A standard networking architecture that defines the physical layout, lengths, and types of media that can be used. There are many variations of Ethernet, but most use the CSMA/CD network access method.

Ø  EBCDIC (Extended Binary Coded Decimal Interchange Code) A standardized formatting method for both binary and text files for communications and printer control. IBM developed EBCDIC. The acronym EBCDIC is pronounced “eb-see-dick.”

Ø  extranet An area of a company’s network allowing access by nonemployees such as business partners, vendors, and suppliers.

Ø  fiber-optic cable A type of cable that conducts light signals through glass or plastic to generate network signals. Fiber-optic cable allows for transmission rates of 100 megabits per second or greater. It is impervious to electromagnetic interference because it sends light signals rather than electric signals along the cable.

Ø  frame A segment of data. The words “frame” and “data packet” are often used interchangeably, although technically a frame is found at layer 2 of the OSI model and a packet is found at layer 3.

Ø  hexadecimal A numbering method that relies on a base of 16. Hexadecimal digits can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, or F.

Ø  infrared Invisible light at the upper end of the electromagnetic spectrum. It is used in most hand-held remote control devices for televisions, stereos, and videocassette players. It is also used in some types of computer networking, especially for data transfers between laptop and desktop systems.

Ø  Institute of Electrical and Electronics Engineers (IEEE) A technical professional society that fosters national and international standards. Its Web site is www.ieee.org.

Ø  International Organization for Standardization (ISO) An association that attempts to standardize and define items that increase communication and compatibility in many different industries.

Ø  intranet The part of a company’s network that is restricted to employee use only.

Ø  local area network (LAN) A group of computers and other devices typically connected by a cable. A LAN is normally located in a single geographic region such as a building or floor in a building.

Ø  logical address A network address that can be assigned and modified by the person in charge of the network. This type of address appears at the Network layer of the OSI model.

Ø  Logical Link Control (LLC) layer A sublayer of the Data Link layer that forms the connection between the other software in the protocol stack and the networking hardware (such as the NIC and the cables).

Ø  media The cable, glass, or telephone lines that host the signal from one computer to another on a network.

Ø  Media Access Control (MAC) layer A sublayer of the Data Link layer that defines the hardware address of the physical network interface. In addition, it discards corrupted packets and identifies which packets were directed to the local system.

Ø  metropolitan area network (MAN) An intermediate specification that defines networks confined to a fairly restricted geographic area, such as a campus, town, or city. These private networks span multiple geographically separate locations that are near one another.

Ø  network Two or more computers connected by some type of media.

Ø  network interface card (NIC) A hardware device that transmits and receives electronic signals on a network.

Ø  Network layer The third layer of the OSI conceptual networking model, which allows communications to be routed on a network. It provides a logical address for computers on a network.

Ø  network operating system (NOS) Operating software that has networking components built into its structure.

Ø  networking hardware All the physical components of a network, such as the NIC, cable, hub, switch, router, and any related connectors or devices.

Ø  networking software The programs used to run a network.

Ø  Open Systems Interconnection (OSI) A seven-layer reference model created by the International Organization for Standardization (ISO) to define and separate networking hardware and software into distinct layers and functions. This model helps to ensure that the various networking implementations are compatible.

Ø  packet A group of data that is transmitted across a network.

Ø  peer-to-peer network A type of network in which the clients can also function as servers. 

Ø  peer communication The method of communication among the levels of the OSI model, in which each protocol in the OSI protocol stack encodes its own protocol data unit into the network hierarchy, so that it can communicate with the equivalent layer on the destination computer.

Ø  physical address Also called the MAC address. It is burned into the network interface card (NIC) during the manufacturing process.

Ø  Physical layer The first layer of the OSI conceptual networking model, which defines the physical media and electronic transmission methods used in networking.

Ø  Presentation layer The sixth layer of the OSI network model, responsible for data formatting and encryption.

Ø  protocol A definition of rules for communication between two or more computers. Computers must have a common protocol (or a translator) in order to communicate.

Ø  protocol data unit (PDU) Information added to a data packet by the layers of the protocol stack. It can be header or trailer information that is attached to the data packet prior to transmission.

Ø  Remote Procedure Call (RPC) A method used to establish communications between computer systems at the Session layer.

Ø  repeater A device that repeats or boosts a network signal along network wire. It reduces signal degradation and increases the maximum usable length of network cable.

Ø  server A computer that shares resources with other devices on a network.

Ø  Session layer The fifth layer of the OSI model, which controls the connection between two computers sharing data. It maintains, defines, and recovers connections that are established between two computers.

Ø  storage area network (SAN) A subsystem of networked storage devices that are physically separate from the servers.

Ø  Structured Query Language (SQL) A computer language used to query, manipulate, and communicate with databases.

Ø  Transport layer The fourth layer of the OSI reference model, which segments and reassembles data frames. It also provides for connection-oriented and connectionless communications.

Ø  virtual private network (VPN) A private communications link over public communications infrastructure, such as the Internet.

Ø  WAV A Windows Audio file, an audio file format used with Microsoft Windows applications.

Ø  wide area network (WAN) A network that spans two or more geographically diverse locations and typically uses public telecommunications carriers to connect its individual segments.

Ø  wireless Communications that are not conducted over physical wires or cables. These communications can include infrared, radio, and other types of transmissions that are sent through the air between two or more locations.

Ø  X-Windows A standard graphical user interface (GUI) used on UNIX systems.

CH2

Ø  100BaseFX A Fast Ethernet implementation over multimode fiber-optic cabling. The maximum segment length is 412 meters.

Ø  100BaseT4 A 100-Mbps Fast Ethernet implementation that uses four pairs of either Category 3, 4, or 5 UTP cable. The maximum segment length is 100 meters.

Ø  100BaseTX A Fast Ethernet implementation that uses two pairs of either Category 5 unshielded twisted-pair (UTP) or shielded twisted-pair (STP). 100Base-TX operates at 100 Mbps with a maximum segment distance of 100 meters.

Ø  1000BaseCX An IEEE 802.3z Gigabit Ethernet implementation that uses balanced copper cabling to achieve 1000 Mbps.

Ø  1000BaseLX An IEEE 802.3z Gigabit Ethernet implementation that uses single-mode fiber to achieve 1000 Mbps.

Ø  1000BaseSX An IEEE 802.3z Gigabit Ethernet implementation that uses multimode fiber to achieve 1000 Mbps.

Ø  1000BaseT An IEEE 802.3ab Gigabit Ethernet implementation that uses all four pairs of Category 5 or better UTP cable to achieve 1000 Mbps.

Ø  active hub A device that connects multiple nodes and/or networks, is connected to external power, and repeats and regenerates signals on a network.

Ø  ad hoc mode A wireless mode where client devices connect directly to each other without an access point.

Ø  amplifier A device used to boost analog signals on a broadband network.

Ø  analog A method of signal transmission on broadband networks.

Ø  attenuation The natural degradation of a transmitted signal over distance.

Ø  backoff period A random time interval used after a collision has been detected on an Ethernet network. Use of a backoff period minimizes the likelihood of another collision.

Ø  bandwidth The available capacity of the network. The greater the network bandwidth, the greater the speed in data transfer.

Ø  Basic Service Set (BSS) A wireless network with only one access point connected to a switch.

Ø  bridge A device that operates at the Data Link layer, used to filter traffic between network segments by evaluating the MAC address of packets that are sent to it.

Ø  broadcast A frame meant for the entire network.

Ø  broadcast domain A group of network devices that will receive LAN broadcast traffic from each other.

Ø  broadcast storm Excessive broadcast messages to every host on the network, launched by multiple computers; usually triggered by some error condition on the network.

Ø  brouter A device that functions as a bridge for nonroutable protocols and a router for routable protocols. The brouter operates at both the Data Link and Network layers.

Ø  Carrier Sense Multiple Access with Collision Detection (CSMA/CD) An access method specified by the IEEE Ethernet 802.3 standard. In this method, a node will listen to see if the line is clear and then, if the line is clear, send data. Two nodes may still send at the same time and cause a collision, in which case the two nodes will then perform the backoff algorithm.

Ø  carrier signal A transmitted electromagnetic pulse or wave on the network wire that indicates a transmission is in progress.

Ø  collision domain In Ethernet networking, a single segment on a network. Any station on the same physical segment or separated by a repeater is in the same collision domain. Bridges, routers, and switches (depending on how they are configured) can separate collision domains.

Ø  contention The condition that occurs when computers on a network must share the available capacity of the network wire with other computers.

Ø  Ethernet See Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

Ø  Fast Ethernet Defined in IEEE 802.3u, and includes any of the following 100-Mbps Ethernet LAN technologies: 100Base-T4, 100Base-TX, 100Base-FX.

Ø  Extended Service Set (ESS) A wireless network with multiple access points connected to switches. The access points are typically configured with the same network name (SSID) to facilitate roaming.

Ø  Extensible Authentication Protocol (EAP) Works with 802.1x to carry the authentication information between the user, the access point, and the security server.

Ø  full-duplex A connection that allows communication in two directions at once; common telephone connections are typically full-duplex because people can talk and listen at the same time.

Ø  gateway A combination of hardware and software that translates between different protocols on a network.

Ø  Gigabit Ethernet Includes IEEE 802.3z and IEEE 802.3ab, which allow for speeds up to 1000 Mbps.

Ø  10 Gigabit Ethernet (10GbE or 10 GigE) A standard ten times faster than gigabit Ethernet that is always implemented as full duplex.

Ø  half-duplex A connection that allows communication in two directions, but not simultaneously; the circuit can be used for sending or receiving bits in only one direction at a time.

Ø  hub An active or passive device that connects network segments. Passive hubs are connection points; active hubs repeat and regenerate signals.

Ø  IEEE 802.1x The IEEE standard that defines port switching designed to shut down a switch port to all frames unless they are authentication frames.

Ø  IEEE 802.11 The IEEE standard that defines wireless networking in the unlicensed frequency bands 2.4 GHz and 5 GHz.

Ø  IEEE 802.11i The most robust wireless security standard in use today. It is based on Wi-Fi Protected Access version 2 (WPA2) which uses AES encryption, dynamic keys, and user authentication via 802.1x and EAP.

Ø  IEEE 802.3ab The IEEE standard that defines the Gigabit Ethernet implementation 1000BaseT.

Ø  IEEE 802.3u The IEEE standard that defines Fast Ethernet implementations, including 100Base-T4, 100Base-TX, and 100Base-FX.

Ø  IEEE 802.3z The IEEE standard that defines Gigabit Ethernet implementations including 1000BaseCX, 1000BaseLX, and 1000BaseSX.

Ø  infrastructure mode A wireless mode in which the access point is wired back into a switch so that the client has access to the LAN and WAN, not just the WLAN.

Ø  interframe gap (IFG) The time required between the transmission of data frames on the network: 9.6 microseconds.

Ø  interpacket gap (IPG) See interframe gap.

Ø  internetwork A large network comprised of smaller interconnected networks.

Ø  IP address A 32-bit binary address used on TCP/IP networks; consists of a host portion and a network portion.

Ø  jam signal A 32-bit signal that is sent by the first station to detect a collision on an Ethernet network; ensures that all other stations are aware of the collision.

Ø  latency A delay on a network caused by a variety of factors, including the addition of devices.

Ø  media access method See network access method.

Ø  microsegmentation The type of segmentation that occurs through the use of virtual circuits between switches and nodes. Each connection enjoys the total bandwidth. Bandwidth is not shared as it is through hubs.

Ø  network access method The process by which network interface cards and devices communicate data on a network; an example is CSMA/CD. Also known as media access method.

Ø  node A connection point or junction on the network. A node can be a terminal or computer connected to the network.

Ø  optical repeater A network device that uses LEDs or diode lasers to amplify optical signals.

Ø  passive hub A device that connects network segments but does not perform signal regeneration.

Ø  port A connection point, usually for network cable, on a device such as a hub, bridge, switch, or router.

Ø  repeater A device that repeats and cleans signals on the network and extends the usable distance of the network.

Ø  router A device that connects multiple segments, subdivides a network, filters broadcast traffic, and maintains a routing table. A router uses the logical address to move data packets from point to point.

Ø  segment (noun) A section of a network that has been subdivided by routers, switches, or bridges.

Ø  segment (verb) To subdivide a network with a networking device, such as a bridge, switch, or router.

Ø  segmentation The process of breaking a network into smaller broadcast or collision domains.

Ø  Service Set Identifier (SSID) The network name configured on both the access point and the client so that they can communicate.

Ø  subnetwork A portion of the network created by manipulating a network address and breaking it down into smaller parts.

Ø  switch A device used between nodes on a network or between networks to create virtual circuits between two points. A switch increases bandwidth by isolating traffic between two points.

Ø  Token Ring A networking method developed by IBM that organizes the network into a physical or logical ring. The token is a logical device, and because stations may only broadcast on the network when they have the token, traffic does not collide.

Ø  topology The physical layout of network components. The topology can take the form of a ring, star, or bus.

Ø  virtual circuit A private connection between two points created by a switch that allows the two points to use the entire available bandwidth between them without contention.

Ø  WEP (Wired Equivalent Privacy) The initial wireless security standard that uses the RC4 algorithm with static key. This is now considered weak encryption.

Ø  WPA (Wi-Fi Protected Access) The improvement to WEP. It provides better encryption with the TKIP algorithm and dynamic keys.

Ø  WPA2 (Wi-Fi Protected Access version 2) The upgrade to WPA that provides the more robust AES algorithm for encryption as well as dynamic keys. Both WPA and WPA2 can be configured to use 802.1x/EAP.

Ø  wireless access point A network device that contains a radio transceiver, which allows wireless clients to connect to a WLAN.

Ø  wireless local area network (WLAN) A local area network consisting either entirely of wireless clients or a traditional LAN that contains wireless access points.

CH3:

Ø  Address Resolution Protocol (ARP) A protocol that works at the Internetwork layer of the TCP/IP networking model; resolves a known IP address to an unknown MAC address, which is the final leg of communication between the source and destination.

Ø  Advanced Research Projects Agency (ARPA) The government organization operating in the Department of Defense (DOD) that was responsible for the creation and proliferation of the Internet and the TCP/IP protocol suite.

Ø  Advanced Research Projects Agency Network (ARPANET) The original name of the Internet.

Ø  Application layer The TCP/IP layer that corresponds to the Application, Presentation, and Session layers of the OSI model.

Ø  ARP reply A reply sent by the device that discovers its own IP address in the IP header of the ARP request frame and includes the requested MAC address.

Ø  ARP request A process used to obtain the correct mapping when a source computer cannot locate a destination MAC address for a known IP address in its ARP table.

Ø  ARP table A table used by a network device that contains MAC to IP address mappings.

Ø  buffer A portion of memory used to store information that is being sent or created too fast for a system to process.

Ø  buffering A method in which devices on a network handle packet flows that exceed their processing capabilities. Packets are stored in a buffer until the system can process them.

Ø  Cisco Three-Layer Hierarchical model A model that emphasizes good network design and involves the access layer at the bottom, the distribution layer in the middle, and the core layer at the top.

Ø  congestion avoidance A method by which a system on a network can reduce the flow of packets on the network by sending a message request to the sender to reduce the rate at which packets are being transmitted.

Ø  default gateway The address to which a host or IP device sends a packet when the destination host is not on its subnet. The default gateway is usually an interface on a router.

Ø  destination unreachable An ICMP message sent back to the source host when a gateway cannot deliver an IP datagram.

Ø  Dynamic Host Configuration Protocol (DHCP) A protocol used to obtain IP addresses and other parameters such as the default gateway, subnet mask, and IP addresses from a server. DHCP has largely replaced RARP.

Ø  diskless workstation Workstations configured to download their operating systems from a central server. These workstations typically do not have a hard drive.

Ø  Domain Name System (DNS) A hierarchical naming service that is used on the Internet and IP networks to provide host name to IP address resolution.

Ø  echo request/reply The most commonly used ICMP message. ICMP echo request/reply messages are used to check the availability of a remote host and the devices along a network path (intermediate gateways), and to verify the installation of the TCP/IP protocol on the local source host.

Ø  expectational acknowledgment A TCP acknowledgment process in which the acknowledgment number refers to the next expected sequence number. If the expected sequence is not received within a specific time interval, a retransmission is requested.

Ø  File Transfer Protocol (FTP) A part of the TCP/IP protocol suite that provides reliable file transfers across the Internet or other TCP/IP networks. FTP uses TCP to transfer files.

Ø  Hypertext Transfer Protocol (HTTP) A protocol used for communications on the World Wide Web. Web servers are HTTP servers.

Ø  ICMP flood A large quantity of ICMP echo requests sent to a target device by a malicious person or program in an attempt to crash or greatly reduce the performance of the target device.

Ø  information request/reply ICMP messages that are typically used to determine the subnet mask used by the destination. This message allows a host to determine the number of the network on which it resides.

Ø  initial sequence number (ISN) Sequence numbers that allow communicating hosts to synchronize their communications in a TCP three-way handshake. When the communication is initiated, two hosts communicating over TCP will synchronize their initial sequence numbers.

Ø  Internet Control Message Protocol (ICMP) A protocol in the TCP/IP protocol suite at the Internetwork layer. ICMP messages control and manage IP protocol communications.

Ø  Internet Protocol (IP) The Network layer (Internetwork layer) protocol that is responsible for logical addressing. This allows data to be routed.

Ø  Internetwork layer The layer of TCP/IP that is equivalent to the Network layer of the OSI model.

Ø  IP addressing The process of assigning (unique) IP addresses to devices on the network either by typing them in statically or using a dynamic approach such as RARP or DHCP.

Ø  link-state A routing protocol that uses cost when calculating the best path between two points. It considers items such as network traffic, router congestion, bandwidth, reliability, and other factors that could affect network performance.

Ø  Network File System (NFS) A file system associated with the UNIX operating system that allows for network communications between hosts.

Ø  Network Interface layer In TCP/IP, the layer that is equivalent to the Physical and Data Link layers of the OSI model.

Ø  Packet Internet Groper (Ping) A troubleshooting utility that uses ICMP to verify that a remote host is currently running and accessible.

Ø  parameter problem An ICMP message sent whenever incorrect datagram header information is received. The message identifies the octet in the datagram that caused the problem.

Ø  Post Office Protocol version 3 (POP3) A protocol used by client machines that allows users to download e-mail from an e-mail server.

Ø  redirect An ICMP message sent to source hosts requesting that they change routes because the one they chose was not optimal. This packet is used to update a source host’s internal routing table.

Ø  remote login application (rlogin) A utility that allows remote computers to connect to other computers or devices.

Ø  Requests for Comments (RFC) A group of Internet-related documents that specify Internet protocols and standards.

Ø  reset packet (RST) A packet indicating that the receiver should delete the TCP connection without further interaction.

Ø  Reverse Address Resolution Protocol (RARP) A protocol used to resolve the client’s unknown IP address to the client’s MAC address for the final leg of communication between an IP source and destination. RARP clients broadcast a request for their IP address. A RARP server has a table of IP to MAC mappings and responds to the client with a RARP reply.

Ø  routed protocol A protocol that contains enough OSI Network layer information that its packets can be routed from a source to a remote destination on an internetwork.

Ø  routing protocols Used to dynamically create routing tables so that routed protocols can route the data.

Ø  routing table A table used by a router to determine which of its interfaces is connected to the destination network.

Ø  Simple Mail Transfer Protocol (SMTP) The main protocol that transfers electronic mail on the Internet between e-mail servers.

Ø  Simple Network Management Protocol (SNMP) A protocol that provides network administrators the ability to centrally control and monitor the network.

Ø  sliding windows A feature of TCP used to control the flow of communications between two hosts. The size of the TCP sliding window regulates how often acknowledgments will be sent to the transmitting host from the receiving host.

Ø  source quench An ICMP message request to reduce the rate at which the sender is transmitting packets to the destination. This message is used for flow control, when packets arrive too fast (the receiving host runs out of buffer space for the message), or if the system is near capacity (network is congested).

Ø  TCP/IP See Transmission Control Protocol (TCP) and Internet Protocol (IP).

Ø  terminal emulation protocol (telnet) A connection-oriented, Application layer utility that allows TCP/IP clients to log in to a remote system and operate on that system as if the connection between the two were local.

Ø  three-way handshake The method used by TCP to negotiate a reliable connection between two hosts on a network. This process involves the exchange of three data packets before the communication process begins.

Ø  time exceeded An ICMP message sent whenever a packet’s time-to-live (hop count) reaches zero and the datagram is dropped.

Ø  time-to-live (TTL) The number of hops (routers) that a packet can make before it is discarded. The router discards a packet when its TTL is zero, which prevents a packet from looping endlessly around the network. Routers normally decrement the packet TTL by 1 before passing the packet to the next router.

Ø  timestamp request/reply ICMP messages that are used to synchronize clocks by requesting the destination machine’s current time of day value, which is given in milliseconds from midnight Universal Time.

Ø  Trace A utility that uses ICMP messages to determine the path between a source and destination host. Trace can discover all of the hops (routers) along the path between two points.

Ø  Transmission Control Protocol (TCP) The protocol that guarantees the delivery of a packet by sending an acknowledgment for each window of data received. This protocol operates at the Transport layer and sends its data encapsulated in the IP protocol. TCP communications are considered connection-oriented because TCP negotiates a communication path between hosts on the network.

Ø  Transport layer The TCP/IP layer that maps directly to the OSI model Transport layer.

Ø  Trivial File Transfer Protocol (TFTP) A file transfer utility used on the Internet. TFTP uses UDP to transfer files and is therefore less reliable than FTP, which uses TCP in transferring files.

Ø  UDP (User Datagram Protocol) The protocol that operates at the Transport layer and transports data unreliably over IP. This is sometimes known as connectionless communication because the messages are sent without expectation of acknowledgment. Unlike TCP, UDP has no connection negotiation process. The packets that are sent by UDP are also known as datagrams. Because UDP does not negotiate a connection, it is faster than TCP.

Ø  Well Known Port numbers TCP and UDP ports from 0 through 1023 on which client applications expect to find common Internet services.

CH4

Ø  American Registry of Internet Numbers (ARIN) An organization that manages IP address allocation in the United States.

Ø  classful A routing process that involves using subnet masks with traditional octet boundaries.

Ø  classless A routing process that allows subnet masks to partition the network and the node portions on any bit boundary.

Ø  Classless Inter-Domain Routing (CIDR) A system of allocating IP network numbers based on arbitrary subnet mask boundaries. CIDR notation uses a prefix to designate the network portion of the subnet mask.

Ø  directed broadcasts Broadcasts sent to specific segments. For example, a broadcast on segment 192.168.1.0 would be 192.168.1.255.

Ø  dual stack An IPv6 transition method that allows for both IPv4 and IPv6 stacks to be run on the network at the same time.

Ø  flooded broadcasts A broadcast for any subnet that uses the IP address 255.255.255.255. Routers do not pass flooded broadcasts.

Ø  hexadecimal A base 16 numbering system that uses numerals 0 through 9 and the letters A through F to represent numbers. MAC addresses and IPv6 addresses are displayed in hexadecimal.

Ø  Internet Assigned Numbers Authority (IANA) The regulatory agency originally responsible for subdividing and administering the address hierarchy used on the Internet. IANA has been replaced by ICANN.

Ø  Internet Corporation for Assigned Names and Numbers (ICANN) The global, government-independent entity responsible for the Internet.

Ø  IP addressing The act of assigning (unique) IP addresses to devices on the network.

Ø  IP Security Protocol (IPSec) A suite of protocols that provide authentication and encryption at layer 3.

Ø  IPv4 The currently deployed system of IP addressing involving 32-bit numbers expressed as decimal numbers in four octets.

Ø  IPv6 The newest version of IP addressing that involves 128-bit addresses expressed as hexadecimal numbers.

Ø  loopback The TCP/IP Class A address 127.x.x.x that is reserved for diagnostic purposes. Any address on this network allows you to check if TCP/IP has been properly installed on the system. (Specifically, the IP address 127.0.0.1 is the address usually given as the loopback.)

Ø  multicast address A special subdivision of IP categories reserved for data streaming. Multicast addresses are used to send information to groups of computers. The range for multicasting addresses is 224.0.0.0 to 239.255.255.255.

Ø  multicasting The sending of a stream of data to multiple computers simultaneously.

Ø  Network Address Translation (NAT) A standard that allows inside IP addresses to be translated to different outside IP address(es). NAT maps inside IP addresses to different outside IP addresses or just one outside address. NAT is used to slow the exhaustion of IPv4 addresses as well as to hide a company’s internal IP scheme.

Ø  nibble Four bits. There is one hexadecimal digit in a nibble.

Ø  prefix A way of designating the subnet mask that involves a forward slash followed by the number of binary ones in the mask; in other words, the network portion.

Ø  subnet A portion of a network that has been separated from the main network by using a different subnet mask.

Ø  subnet mask A required component for all IP hosts used in combination with an IP address to determine to which subnet the local host belongs. The local host uses this information to determine if the destination is local or remote to the source. Based on this information, the source will either broadcast information on the local network or send its packet to the default gateway for delivery to a remote network.

Ø  subnetting The act of subdividing a network logically with subnet masks.

Ø  summarization The advertisement of many routes as a single route to reduce the total number of route table entries on a router.

Ø  supernetting Also known as summarization or route aggregation. Done by moving the network/node boundary in the subnet mask to the left to include more than one network in an advertisement.

Ø  tunneling An IPv6 transition strategy that involves encapsulating IPv6 packets inside of IPv4 packets so they can traverse the non-IPv6 portion of the network.

Ø  variable length subnet masking (VLSM) The use of different masks on different subnets, which allows for more efficient IP address allocation. Supported by advanced routing protocols such as RIP version 2, OSPF, and EIGRP.

CH5:

Ø  AUX line password A password used to access the router through the AUX port.

Ø  AUX port See auxiliary port (AUX).

Ø  auxiliary port (AUX) A secondary port that allows connection to a modem that will be used for direct access to the router for configuration.

Ø  bootstrap A small program used to load a much larger program. In the case of a router or switch, the bootstrap program loads the IOS.

Ø  Cisco Internetwork Operating System (IOS) A router operating system that provides a command-line interface, which allows network operators to check the status of the router and allows network administrators to manage and configure the router.

Ø  command executive The user interface that interprets commands and is provided by the Cisco IOS (also known as the EXEC).

Ø  console A physical connection on the back of the router to which you can connect a rollover cable to attach to a PC for router configuration (also known as a console port).

Ø  console password The password that is used to access the router through the console port.

Ø  console port See console.

Ø  context-sensitive Help Help with the syntax of commands for the router that is based on the current router mode and prompt, as well as any part of a command that is typed.

Ø  Coordinated Universal Time (UTC) Based on the time in the city of Greenwich in the United Kingdom. All other time zones are either plus or minus hours of the time in Greenwich.

Ø  dynamic random access memory (DRAM) See random access memory (RAM).

Ø  enable mode Another name for the privileged EXEC mode. The enable or enable secret password must be entered in order to access this mode.

Ø  enable mode prompt The prompt that indicates operation in privileged EXEC or enable mode. It has two elements: the host name of the router and the pound (#) symbol.

Ø  enable password The password that protects enable mode in the event that the enable secret password has been removed.

Ø  enable secret password An MD5-encrypted password that is not visible when viewing the system configuration; it supersedes the enable password.

Ø  EXEC See command executive. 

Ø  flash memory Erasable, programmable, read-only memory (EPROM). The content of flash memory is maintained when the router is rebooted. Flash memory contains the working copy of the Cisco IOS and it is the component that initializes the IOS for normal router operations.

Ø  global configuration mode A router mode that allows manipulation of most of the router’s generic settings. The prompt for global configuration mode is router(config)#.

Ø  interface configuration mode A router mode that allows you to configure the Ethernet and serial interfaces. The prompt for this mode is router(config-if)#.

Ø  line configuration mode A router mode that allows you to configure the virtual terminals, console, and AUX lines that let you access the router. The prompt for this mode is router(config-line)#.

Ø  MD5 algorithm An algorithm used to encrypt an enable secret password.

Ø  nonvolatile random access memory (NVRAM) A special type of RAM that is not cleared when the router is rebooted. The startup configuration file for the router is stored in NVRAM.

Ø  privileged EXEC mode A router mode used to configure the router.

Ø  random access memory (RAM) Memory that stores the working copy of the router configuration. This configuration is erased if the router is rebooted, unless it is saved to the startup configuration.

Ø  read-only memory (ROM) Memory that contains the necessary routines to boot the system and check its hardware. It also contains a limited version of the Cisco IOS for use only when the primary copies of the IOS in flash memory or on a TFTP server are accidentally lost.

Ø  RJ-45 to DB-9 A connector that ships with the router to enable connection to a PC with a DB-9 COM port to the router console port.

Ø  RJ-45 to RJ-45 rollover cable A cable that connects the console port on the back of the router to an RJ-45 to DB-9 connector on the back of a PC. This cable ships with the router.

Ø  ROM monitor mode A router mode that allows you to configure your router in the event that no valid IOS file is in your flash memory.

Ø  router configuration mode A router mode that allows you to enable routing protocols such as RIP and IGRP. The prompt for router configuration mode is router(config-router)#.

Ø  router# See enable mode prompt.

Ø  router> See user EXEC mode.

Ø  system configuration dialog An automated setup routine that runs if you type “setup” from privileged EXEC mode or if the router is started/restarted without a configuration file.

Ø  Trivial File Transfer Protocol (TFTP) server A computer that provides TFTP services and can be used to maintain the IOS and configuration file of a Cisco router.

Ø  user EXEC mode A router mode that allows a network operator to check router status, see if the interfaces are operational, and review several of the router settings.

Ø  user mode See user EXEC mode.

Ø  virtual terminal password A password that is used to access the router over a telnet connection.

Ø  virtual terminals (VTY) Terminals provided with each Cisco router that can be used by telnet sessions to configure the router.

Ø  volatile Contents of memory that are lost when the power is turned off. RAM is an example of volatile memory.

Ø  VTY A Cisco IOS abbreviation for virtual terminal used in commands to reference virtual terminals.

CH6:

Ø  Cisco Discovery Protocol (CDP) A Cisco proprietary Data Link layer protocol that shares configuration information between Cisco devices that are locally connected.

Ø  configuration register A feature in Cisco routers that is stored in NVRAM and allows the administrator to control several boot functions.

Ø  counters Detailed statistics kept by a router about data passing across its interface.

Ø  DCE (data communication equipment) Equipment that performs some type of signal conversion between the terminal device and the transmission facility. Usually the DCE is part of the telco provider’s equipment.

Ø  extended mode ping When you type ping at the privileged EXEC prompt and then press the Return or Enter key, you will be presented with ping options. Extended mode ping options include the destination address of the ping, the protocol, repeat count, and datagram size.

Ø  global configuration mode A router mode that allows you to manipulate most of the router’s generic settings. The prompt for global configuration mode is router(config)#.

Ø  keepalive frames Data frames sent between two hosts to ensure that the connection between those hosts remains open.

Ø  password recovery A method of bypassing the router passwords. This cannot be done remotely.

Ø  power-on self-test (POST) A diagnostic program in ROM that runs when the router is powered on. POST checks hardware availability.

Ø  ROM Monitor A bootstrap program that runs during the power-on self-test and checks basic operations of hardware, including CPU, memory, and interfaces.

Ø  ROM Monitor mode A router mode in which you can configure the router manually.

Ø  RxBoot mode A configuration mode that can be entered when changes to a system make it impossible to boot from the flash memory and a valid IOS image cannot be located.

Ø  Security Device Manager (SDM) A Web-based tool for configuring complex security and other parameters on a Cisco router.

Ø  startup-config The router configuration that loads from NVRAM into RAM when the router boots up.

Ø  Trivial File Transfer Protocol (TFTP) server A computer, such as a PC, laptop, or UNIX workstation, that can be used to maintain Cisco IOS versions and Cisco router configuration files. TFTP is a protocol that is used to copy files back and forth from a computer running TFTP server services.

CH7:

Ø  administrative distance A value used to determine the reliability and desirability of a particular routing table update.

Ø  autonomous system (AS) A group of routers under the control of a single administration.

Ø  Border Gateway Protocol (BGP) An Exterior Gateway Protocol used to route between multiple autonomous systems.

Ø  convergence The point at which all routers on a network share a similar view of the network.

Ø  count-to-infinity A routing loop whereby packets bounce infinitely around an internetwork.

Ø  default route A static route that directs all traffic not specified anywhere else in the routing table to a particular route. Same as quad zero route.

Ø  defining a maximum A technique used with distance-vector routing protocols to prevent packets from bouncing infinitely throughout an internetwork by setting a maximum hop count.

Ø  distance-vector A routing protocol that functions by broadcasting the entire routing table periodically to all connected neighbors; examples include RIP and IGRP.

Ø  dynamic routing protocol A protocol that builds the routing table automatically. Examples include RIP, IGRP, EIGRP, and OSPF.

Ø  Enhanced Interior Gateway Routing Protocol (EIGRP) A proprietary Cisco routing protocol developed to overcome some of the limitations associated with distance-vector protocols. EIGRP is considered a hybrid routing protocol.

Ø  Exterior Gateway Protocol (EGP) A gateway protocol used to route between multiple autonomous systems.

Ø  flood The process of multicasting packets onto a network.

Ø  flush interval The time at which a route is totally removed from the routing table.

Ø  hold-down timer A technique used to stop routing loops in which updates from an inferior source are not allowed for a certain interval. Used by routers to stabilize routing tables and to prevent erroneous routing table updates.

Ø  hop count A count of the number of routers a packet must pass through to reach a destination network.

Ø  Interior Gateway Protocol (IGP) A gateway protocol used to route within one autonomous system.

Ø  Interior Gateway Routing Protocol (IGRP) A proprietary Cisco distance-vector routing protocol that uses delay and bandwidth as its default metrics.

Ø  internetwork Multiple networks connected by routers.

Ø  Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX) A routed-protocol stack developed by Novell for use with the Netware network operating system.

Ø  link-state Routing protocols that function via link-state advertisements using link-state packets to inform all routers on the internetwork of routing information. OSPF is the most common link-state routing protocol.

Ø  link-state advertisements (LSAs) Routing information packets used by link-state routing protocols to advertise their local network link information to neighbor routers in an internetwork.

Ø  link-state packets (LSPs) Packets used to send out link-state advertisements.

Ø  logical addresses Layer 3 addresses (also referred to as Network layer addresses) that allow routing protocols to determine the best path to a particular host.

Ø  metric A value used to define the suitability or desirability of a particular route.

Ø  nonroutable protocols Protocols that do not contain Network layer addressing and therefore cannot pass between multiple networks.

Ø  Open Shortest Path First (OSPF) A link-state routing protocol based upon open (nonproprietary) standards.

Ø  peer-to-peer networks Small networks, normally consisting of fewer than 10 computers, in which each computer can give and receive network services.

Ø  quad zero route See default route.

Ø  routed protocols Protocols that contain Network layer addressing and therefore can pass between multiple networks.

Ø  routing by rumor The learning of routes through secondhand information, and not directly from the router experiencing the change. Routing by rumor is characteristic of distance-vector routing protocols.

Ø  Routing Information Protocol (RIP) A distance-vector routing protocol that uses hop count as its only metric.

Ø  routing loops A network state in which packets are continually forwarded from one router to another in an attempt to find the destination network.

Ø  routing protocols Protocols used by routers to define and exchange routing table information in an internetwork.

Ø  Shortest Path First (SPF) algorithm A complex algorithm used by link-state routing protocols to determine the best path in an internetwork.

Ø  split horizon A technique used by routers to prevent routing loops. In short, a router will not send an update for a route via an interface from which it originally received knowledge of that route.

Ø  split horizon with poison reverse A split horizon in which the router responds to attempts to update a route with an update that marks the route in contention as unreachable.

Ø  static route A route manually added by a network administrator to the routing table of a router.

Ø  stub network A network with only one route to the Internet.

Ø  stub router A router that is last in a chain of routers. There is only one path for all hosts connected to this router to get to the outside world.

Ø  topology The physical or logical structure of a network.

Ø  Transmission Control Protocol/Internet Protocol (TCP/IP) Routed protocol stack developed in the late 1960s for use on the network that preceded the Internet; protocol stack of the modern-day Internet.

Ø  triggered updates Updates that occur due to network topology changes, not periodic routing table advertisements.

CH8:

Ø  adjacencies database The neighbor database in OSPF.

Ø  adjacency Bidirectional communication formed by EIGRP neighbors.

Ø  area An OSPF concept used to define the confines within which LSAs will propagate.

Ø  backup designated router (BDR) An OSPF router on broadcast, multiaccess networks that takes over if the DR fails.

Ø  classful routing protocol A dynamic routing protocol that does not carry subnet mask information in its routing table updates and consequently must summarize to major classful network boundaries.

Ø  classless routing protocol A dynamic routing protocol that carries subnet mask information in its routing table updates; allows support for discontiguous subnets and VLSM.

Ø  cost The default metric in OSPF, calculated with the following equation: Cost = (10^8 /bandwidth of the link).

Ø  designated router (DR) Used on broadcast, multiaccess OSPF networks as a central point for adjacencies and LSAs.

Ø  Diffusing Update Algorithm (DUAL) The algorithm used by EIGRP for path selection.

Ø  Dijkstra’s Shortest Path First Algorithm A complex algorithm used by OSPF routers to determine a loop-free, lowest-cost path to a destination network.

Ø  Enhanced Interior Gateway Routing Protocol (EIGRP) A Cisco proprietary distance-vector protocol that uses some link-state features to improve performance.

Ø  feasibility condition A condition (RD < FD) that allows a route to become a feasible successor.

Ø  feasible distance (FD) The lowest-cost metric to a destination.

Ø  feasible successor A backup route in the EIGRP topology table.

Ø  link An OSPF router interface.

Ø  link-state The status of an interface on an OSPF router.

Ø  MD5 Message Digest 5, an algorithm used to produce a secure hash of shared secret passwords.

Ø  Open Shortest Path First (OSPF) A classless link-state routing protocol that uses areas to provide for hierarchical network design.

Ø  Protocol Dependent Modules (PDMs) A component of EIGRP that allows it to support multiple routed protocols such as IP, IPX, and AppleTalk.

Ø  Reliable Transport Protocol (RTP) A Transport layer protocol used by EIGRP.

Ø  reported distance (RD) The distance an EIGRP router advertises to its neighbors for a network.

Ø  router ID A router identifier used in OSPF Hellos and updates; normally the highest configured loopback or interface address.

Ø  successor The best route to a destination in an EIGRP network.

Ø  topological database A database that holds the common view of the network formed from the link-state advertisements that are received. It allows the router to run the Shortest Path First algorithm and find the best path to a network.

CH9:

Ø  bindings IP to MAC address mappings that are found in the DHCP database.

Ø  DHCP ACK A unicast acknowledgement sent by the DHCP server to the client.

Ø  DHCP DISCOVER A packet that is broadcast on bootup by a client when that client has no IP information or incomplete IP information.

Ø  DHCP OFFER A unicast reply by a DHCP server to a client that has broadcast a DHCP DISCOVER packet.

Ø  DHCP relay If no DHCP service is found on the network, the router can be configured to relay the request to a DHCP server on a different network.

Ø  DHCP REQUEST A formal request for IP configuration information intended for a specific DHCP server but broadcast so that all servers can see the association.

Ø  DNS Domain Name Services provides name-to-IP address translation so that users can use names instead of addresses in commands.

Ø  DHCP Dynamic Host Configuration Protocol provides IP configuration information to clients when they bootup.

Ø  dynamic NAT A type of network address translation in which the valid external IP addresses to be mapped to internal addresses are floating or not fixed. The NAT router can then dynamically assign any of the available external addresses to any of the hosts on the internal network.

Ø  lookup The process of retrieving an IP address for a given name and providing it to the client that requested it.

Ø  network address translation (NAT) A method for using a router to separate an internal network from an external network (usually the Internet), which is defined in RFC 3022. Internal hosts with private or unregistered IP addresses can effectively use one or more public registered IP addresses to communicate with external systems.

Ø  overlapping When an organization wants to connect to the Internet, but its internal addressing scheme is registered to another entity. Instead of renumbering the internal network, the organization uses NAT to translate its internal addressing scheme to the addresses that it was assigned by the ISP.

Ø  overloading A type of NAT that allows multiple internal hosts to use one or more external IP addresses. The NAT router uses a table to keep track of the IP addresses and ports of each host, dynamically mapping each internal socket to a valid external socket.

Ø  port address translation (PAT) A process used in overloading that allows multiple internal, unregistered IP addresses to use a single external registered address.

Ø  port forwarding A method for sending packets from an external host system through a firewall or NAT router to an internal device. In this way, the internal device IP address is hidden from the external network, yet the internal device can still service requests from the external network.

Ø  static NAT A type of network address translation (NAT) that allows for a one-to-one mapping of internal to external addresses. One internal address is mapped to one specific external address.

CH10:

Ø  access lists Permit or deny statements that filter traffic based on criteria such as source address, destination address, and protocol type.

Ø  any A keyword used to represent all hosts or networks; replaces 0.0.0.0 255.255.255.255 in an access list.

Ø  established A keyword that requires traffic to have originated inside the trusted network.

Ø  extended IP access lists IP access lists that filter traffic by source IP address, destination IP address, protocol type, and port number.

Ø  host A keyword for an extended IP list that specifies that an address should have a wildcard mask of 0.0.0.0.

Ø  implicit deny any Blocks all packets that do not meet the requirements of the access list. Exists at the end of all lists.

Ø  inbound A direction parameter used when applying an access list. Direction is into the router.

Ø  inverse mask See wildcard mask.

Ø  named access list An access list that uses names instead of number ranges.

Ø  outbound A direction parameter used when applying an access list. Direction is out of the router.

Ø  partial masking When an octet in a wildcard mask contains a mix of binary 1s and 0s.

Ø  standard IP access lists Access lists that filter traffic based on source IP address.

Ø  wildcard mask Applied to IP addresses to determine if an access list line will act upon a packet. Zeros are placed in positions deemed significant, and 1s are placed in nonsignificant positions.

CH11:

Ø  100Base-FX A Fast Ethernet implementation over multimode fiber-optic (MMF) cabling. The maximum segment length is 412 meters.

Ø  100Base-T4 A 100-Mbps Fast Ethernet implementation that uses four pairs of either Category 3, 4, or 5 UTP cable. The maximum segment length is 100 meters.

Ø  100Base-TX A Fast Ethernet implementation that uses two pairs of either Category 5 unshielded twisted-pair (UTP) or shielded twisted-pair (STP). 100Base-TX operates at 100 Mbps with a maximum segment distance of 100 meters.

Ø  5-4-3 rule The networking rule that stipulates that between stations on a 10-Mbps half-duplex LAN, there can be no more than five wire segments connected, four repeaters or hubs between the segments, and three populated hubs.

Ø  adaptive cut-through A method of switching whereby the switch uses the cut-through technique unless network errors reach a certain threshold; then, it automatically switches to store-and-forward switching until the error rate returns to an acceptable level. Also known as error sensing.

Ø  alignment error A frame that has both an FCS error and an entire octet missing from the frame.

Ø  asymmetric switching A type of LAN switching that allows for multiple speeds of network communication; a switch that supports both 10-Mbps and 100-Mbps communications is an example of asymmetric switching.

Ø  backoff period A random interval used by devices that have caused a collision on an Ethernet network, during which the devices cannot send, to prevent them from immediately causing another collision.

Ø  bit time The duration of time to transmit one data bit on a network, which is 100 nanoseconds on a 10-Mbps Ethernet network or 10 nanoseconds on a 100-Mbps Ethernet network.

Ø  bridge A device that segments a network at the Data Link layer by filtering traffic based on the MAC address.

Ø  bridge protocol data unit (BPDU) Data packets sent between switches that support the spanning tree protocol.

Ø  bridging table A table maintained on a bridge that maps MAC addresses to the bridge port through which they can be accessed.

Ø  broadcast A frame that is addressed to all stations on the broadcast domain. The destination MAC address is set to FFFFFFFFFFFF so that all local stations will process the packet.

Ø  broadcast storm An error condition in which broadcast traffic is above 126 packets per second and network communications are impeded. This is typically the result of a software configuration error or programming error.

Ø  Carrier Sense Multiple Access with Collision Detection (CSMA/CD) An Ethernet networking method defined by IEEE standard 802.3, which states that an Ethernet station must first listen before transmitting on a network. Any station can transmit as long as there are no transmissions active on the network. If two stations transmit simultaneously, a collision will occur, and the stations must detect the collision and reset themselves.

Ø  carrier signal A transmitted electromagnetic pulse or wave on the network wire that indicates a transmission is in progress.

Ø  collision domain The area on a network in which collisions can occur; a section of the network that is not separated by routers, switches, or bridges.

Ø  configuration bridge protocol data unit (CBPDU) See bridge protocol data unit (BPDU).

Ø  content-addressable memory (CAM) A memory location on a switch that contains the MAC address-to-switch port mapping information, which the switch uses to forward frames to the appropriate destination.

Ø  contention method The method by which computers on a network must share the available capacity of the network wire with other computers.

Ø  cut-through A switching technique in which an Ethernet frame is forwarded immediately after the destination address is deciphered. This method offers the lowest latency, but does not reduce packet errors.

Ø  error sensing See adaptive cut-through.

Ø  Ethernet See Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

Ø  Fast Ethernet Defined in IEEE 802.3u, and includes any of the following 100-Mbps Ethernet LAN technologies: 100Base-T4, 100Base-TX, 100Base-FX.

Ø  fast forward Indicates that a switch is in cut-through mode.

Ø  fragment-free A method of switching whereby the switch reads the first 64 bytes of the incoming frame before forwarding it to the destination port(s).

Ø  frame check sequence (FCS) A calculation based on the size of a transmitted data frame that verifies whether it was received intact.

Ø  frame check sequence (FCS) error An error that occurs when the calculation in the FCS field indicates that a frame was not received intact.

Ø  full-duplex A connection that allows communication in two directions at once; common telephone connections are typically full-duplex because people can talk and listen at the same time.

Ø  gateway A combination of software and hardware that translates between different protocol suites.

Ø  giant See long frame.

Ø  half-duplex A connection that allows communication in two directions, but not simultaneously; the circuit can be used for sending or receiving bits in only one direction at a time.

Ø  IEEE 802.3u The IEEE standard that defines Fast Ethernet implementations, including 100Base-T4, 100Base-TX, and 100Base-FX.

Ø  interframe gap The time required between the transmission of data frames on the network: 9.6 microseconds.

Ø  interpacket gap (IPG) See interframe gap.

Ø  jabber A frame that is longer than the 1518 bytes acceptable for transmission between stations and that also has an FCS error.

Ø  jam signal A 32-bit signal that is sent by the first station to detect a collision on an Ethernet network; ensures that all other stations are aware of the collision.

Ø  late collision A situation that occurs when two stations transmit more than 64 bytes of their frames before detecting a collision.

Ø  latency The lag or delay that a device or part of the network media causes; for example, fiber-optic cable delays a transmitted signal 1 bit time every 10 meters.

Ø  long frame An Ethernet frame that is over the 1518 bytes acceptable for transmission between stations.

Ø  media access method See network access method.

Ø  microsegmentation Increasing the number of collision domains without increasing the number of subnets, for example, when nodes are connected directly to a switch.

Ø  modified cut-through See fragment-free.

Ø  multicast A frame that is addressed to a group of systems; typically used in radio- or television-style broadcasting on the network.

Ø  multimode fiber-optic (MMF) cable Fiber-optic cabling that allows for multiple simultaneous light transmissions.

Ø  multiport bridge Another name for a switch.

Ø  network access method The process by which network interface cards and devices communicate data on a network; an example is CSMA/CD. Also known as media access method.

Ø  NIC error An error that indicates a NIC is unable to transmit or receive a packet.

Ø  port-based memory buffering A memory buffer on a switch assigned by port, equally; does not allow for dynamic allocation of buffer space according to the activity level of a port.

Ø  preamble Binary timing information that precedes an Ethernet frame; used by the receiving station to synchronize its clock circuits so the frame can be received correctly.

Ø  propagation delay See latency.

Ø  protocol analyzer A hardware or software device that can capture and analyze network packets, help you analyze traffic flow and packet errors, and track network problems.

Ø  router A device that segments a network at the Network layer by filtering on logical addresses. Creates networks or subnetworks.

Ø  runt See short frame.

Ø  shared memory buffering Dynamic memory buffer that is shared by all switch ports and allocated according to the needs of the ports; ports that have more activity and larger frames to process are allowed to use more memory buffer space.

Ø  short frame frame that is smaller than the 64-byte minimum frame transmission size required by Ethernet.

Ø  slot time 512 bit times, which should be slightly longer than the time it takes to transmit a 64-byte frame on an Ethernet wire.

Ø  start frame delimiter (SFD) The one-octet binary pattern (10101011) that indicates the preamble is over and that the following information should be considered the actual data frame.

Ø  sticky-learn The process by which a switch automatically learns MAC addresses during communications and configures them as permanent.

Ø  store-and-forward A switching method in which the entire transmitted frame is read into a switch’s buffer before being forwarded by the switch. This method offers the greatest error reduction, but the highest latency. See cut-through and adaptive cut-through.

Ø  switch A device that connects devices on a LAN and segments collision domains by port.

Ø  switched bandwidth A switching technique whereby the total network bandwidth is dedicated to each unicast transmission, even if multiple unicast transmissions are going through the switch at the same time. Unicast traffic between devices on a switch do not share the total bandwidth of the network.

Ø  symmetric switching A type of LAN switching that requires all devices to be operating at the same speed; it does not allow for a mix of 10-Mbps and 100-Mbps communications.  TACACS and Extended TACACS (XTACACS) are defined in RFC 1492.

Ø  transmission time The time it takes for a transmission to go from the source host to the destination host.

Ø  unicast A frame that is sent or addressed to a single destination host; compare with multicast and broadcast.

CH12:

Ø  address The element of the PPP frame represented by the binary sequence 11111111; because PPP is used to create a point-to-point connection, there is no need for PPP to assign an individual address for each host.

Ø  AppleTalk Control Protocol (ATCP) PPP interface protocol for AppleTalk; see Network Control Protocol.

Ø  asynchronous character map The piece of information in the LCP field of the PPP packet that allows PPP to encode its transmission properly for the recipient host.

Ø  authentication The process of verifying the right to complete a connection.

Ø  challenge The query packet, or the action of sending the query packet over a CHAP connection, that is used to verify the participants of the PPP connection.

Ø  Challenge Handshake Authentication Protocol (CHAP) PPP authentication protocol that provides better security than PAP in authenticating devices on PPP connections.

Ø  compression Data compression that can be performed on the PPP packet at the source and then uncompressed at the destination.

Ø  Consultative Committee on International Telephony and Telegraphy (CCITT) The former name of International Telecommunication Union-Telecommunication Standardization Sector (ITU-T).

Ø  control The element of the PPP frame represented by the binary sequence 00000011, which indicates that the transmission of user data will not be sequenced and is to be delivered over a connectionless link.

Ø  data The LCP field is also known as the Data field. This location contains the LCP information and the data that has been encapsulated from the higher layers. The default size of this field is 1500 bytes, but PPP implementations can negotiate a larger size for this field.

Ø  down-when-looped A Cisco router command that shuts down an interface when looping is detected; used to prevent testing scenarios from causing troubleshooting problems in a production environment.

Ø  flag Identifies the beginning and end of the PPP frame.

Ø  Frame Check Sequence (FCS) A mathematical computation placed at the end of the frame; used to ensure that the frame was not corrupted during transmission.

Ø  Frame Relay access device (FRAD) The device that the Frame Relay customer uses to connect to a Frame Relay network; also known as the Frame Relay assembler/disassembler.

Ø  Frame Relay assembler/disassembler See Frame Relay access device (FRAD).

Ø  Frame Relay map A table that defines the interface to which a specific DLCI number is mapped.

Ø  Frame Relay network device (FRND) The device that the Frame Relay provider supplies as the connection to the Frame Relay network; the acronym FRND is pronounced friend.

Ø  Frame Relay switch A telecommunications company device that is used to support Frame Relay connections from customer locations; used to route Frame Relay traffic inside the public data network.

Ø  Frame Relay switching table A table that is maintained on a Frame Relay switch; used to route Frame Relay traffic via virtual circuit DLCI numbers.

Ø  High-Level Data Link Control (HDLC) A common layer 2 WAN protocol that many other WAN protocols are based upon.

Ø  High-Speed Serial Interface (HSSI) Defines a serial connection that operates at speeds of up to 52 Mbps over distances of up to 15 meters (50 feet)

Ø  International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) A standards organization based in Europe, but with membership worldwide; involved in telecommunications standardization.

Ø  IP Control Protocol (IPCP) PPP interface protocol for IP; see Network Control Protocol.

Ø  IPX Control Protocol (IPXCP) PPP interface protocol for IPX; see Network Control Protocol.

Ø  keepalive packets Data packets sent between devices to confirm that a connection should be maintained between them.

Ø  LCP link configuration A process that modifies and enhances the default characteristics of a PPP connection; includes the following actions: link establishment, authentication, link-quality determination, Network layer protocol configuration negotiation, and link termination.

Ø  Link Control Protocol (LCP) Used to establish, configure, maintain, and terminate PPP connections.

Ø  link establishment The process of opening and configuring a PPP connection before any data can be transferred over the link.

Ø  link-quality determination The process of checking the quality of a PPP link and monitoring its reliability.

Ø  Link Quality Monitoring (LQM) PPP feature that checks the reliability of the link by monitoring the number of errors, latency between requests, connection retries, and connection failures on the PPP link.

Ø  link termination The process of disconnecting a PPP connection when the call is complete, which is determined by the PPP hosts that made the connection.

Ø  loopback command A Cisco router command that places an interface in a looped-back state, which means that all outgoing data will be redirected as incoming data without going out on the network; used for testing purposes.

Ø  magic number Unique numbers added by the router to a packet, which allows it to detect a looped-back link.

Ø  maximum receive unit size The piece of information in the LCP field of the PPP packet that sets the receive buffer size for the LCP connection, typically 1500 bytes.

Ø  multilink Allows multiple transmission devices (such as two modems) to send data over separate physical connections; defined in RFC 1717.

Ø  multipoint The configuration of a single interface or subinterface to use multiple virtual circuits.

Ø  Network Control Protocol (NCP) Allows PPP to encapsulate multiple protocols including IP, IPX, and AppleTalk. NCPs are functional fields containing codes that indicate the type of protocol that is encapsulated.

Ø  Network layer protocol configuration negotiation The process of determining a Network layer protocol to use over a PPP connection that is common to both PPP hosts.

Ø  nonbroadcast multiaccess (NBMA) A rule used in Frame Relay that does not allow broadcasts to be sent to multiple locations from a single interface.

Ø  oversubscription When the sum of the data arriving over all virtual circuits exceeds the access rate.

Ø  Password Authentication Protocol (PAP) PPP authentication protocol that provides some security in verifying the identity of devices using PPP connections.

Ø  point-to-point The configuration of one or more interfaces or subinterfaces to connect to multiple virtual circuits. Each circuit will be on its own subnet. Acts like a leased line.

Ø  protocol The element of the PPP frame represented by two bytes used to identify the protocol that is encapsulated.

Ø  public data network (PDN) A telecommunications network that connects telephones around the country. These services can be provided by AT&T, Sprint, MCI, and RBOCs.

Ø  RADIUS server RADIUS is an authentication and accounting server.

Ø  static address to DLCI Frame Relay map A Frame Relay map that has been manually created by a network administrator.

Ø  subinterface A logical division of an interface; for example, a single serial interface can be divided into multiple logical subinterfaces.

Ø  Terminal Access Controller Access Control System (TACACS) An authentication protocol that allows Cisco routers to offload user administration to a central server. TACACS and Extended TACACS (XTACACS) are defined in RFC 1492.

CH13:

Ø  access list A list of criteria to which all packets are compared.

Ø  blocking A port state on a switch that indicates the port is receiving and sending BPDUs, but is not receiving and forwarding data frames in order to prevent logical loops in the network.

Ø  bridge protocol data unit (BPDU) An STP management message used to transfer status information about the Spanning Tree configuration of a switched or bridged network. Also known as configuration bridge protocol data unit (CBPDU).

Ø  broadcast domain A logical or physical group of devices that will receive broadcast traffic from each other on a LAN.

Ø  default VLAN The default configuration of every port on a switch. Same as VLAN 1.

Ø  disabled A port state on a switch that indicates the port is neither receiving BPDUs nor forwarding frames.

Ø  forwarding The state of a port on a switch or bridge that indicates it will learn MAC addresses and forward frames out that port.

Ø  frame filtering A technique used on early VLAN implementations that employed the use of multiple switching tables.

Ø  frame identification See frame tagging.

Ø  frame tagging A method of VLAN identification endorsed by the IEEE 802.1q specification that calls for an additional four-byte field in the VLAN frame after the source and destination addresses in the data packet. Also known as frame identification.

Ø  IEEE 802.10 (FDDI) A frame-tagging method used to identify VLANs trunked across Fiber Distributed Data Interfaces (FDDI).

Ø  IEEE 802.1q The IEEE standard that defines VLAN implementations and recommends frame tagging as the way in which switches should identify VLANs. Used by Cisco switches for compatibility with non-Cisco switches.

Ø  IEEE 802.1w The IEEE standard that governs Rapid Spanning Tree Protocol. See Rapid Spanning Tree Protocol.

Ø  Inter-Switch Link (ISL) protocol A frame-tagging method for VLANs proprietary to Cisco devices; uses a 26-byte header.

Ø  LAN emulation (LANE) A frame-tagging method used for VLANs on Asynchronous Transfer Mode (ATM) devices.

Ø  learning A transitory state on a bridge or switch port that indicates it is trying to learn new MAC addresses and correct its bridge table before forwarding frames on the network; used to prevent loops during the election of a new root bridge.

Ø  listening A transitory state on a bridge or switch port that is used during the election of a new root bridge; the port does not learn MAC addresses, nor does it forward data frames when in this state.

Ø  logical loop A situation that occurs when a packet can be routed in an endless loop around a network, because bridging tables and routing tables reference each other as the destination for a given address.

Ø  management VLAN The default configuration of every port on a switch. Same as VLAN 1.

Ø  Per-VLAN Spanning Tree Protocol (PVSTP) A protocol that operates on VLANs and treats all connected VLANs as separate physical networks.

Ø  physical path loops A loop that occurs when network devices are connected to one another by two or more physical media links.

Ø  Rapid Spanning Tree Protocol (RSTP) The enhanced version of STP that reduces the latency experienced by 802.1d devices in regard to convergence. RSTP is governed by the IEEE 802.1w standard.

Ø  root bridge The bridge or switch that is designated the point of reference (point of origin) in STP operations; also known as a root device.

Ø  root device See root bridge.

Ø  root port The communications port on a nonroot bridge device that is used for BPDU communication between itself and the root bridge.

Ø  Route Switch Module (RSM) A router placed on a switch blade; common with high-end Cisco switches such as the Catalyst 6500.

Ø  router-on-a-stick The process of utilizing one physical router interface (with subinterfaces configured) to route traffic for multiple VLANs.

Ø  Spanning Tree Algorithm (STA) The algorithm used by STP to ensure that logical loops are not created in the presence of physical loops on a network.

Ø  Spanning Tree Protocol (STP) The Data Link layer protocol used by switches and bridges to prevent logical loops in a network, even though physical loops may exist.

Ø  stable state The normal states of ports when the root bridge is available and all paths are functioning as expected.

Ø  transitory state The operating states of ports that prevent logical loops during a period of transition from one root bridge to another.

Ø  virtual LAN (VLAN) A logical broadcast domain on a LAN, created by one or more switches, that is not constrained by the physical configuration.

Ø  VLAN trunking protocol (VTP) A Data Link layer protocol used to track VLAN membership changes across trunk links between VTP-enabled devices.

Ø  VTP client A VTP device that receives and shares VTP information, but does not add, modify, or delete information and does not store the VTP database in NVRAM.

Ø  VTP domain A group of VTP-enabled devices configured under one name to share VLAN information.

Ø  VTP pruning An option configured for an entire VTP domain that prohibits the forwarding of VTP updates about VLANs disabled on specific trunk links.

Ø  VTP server A VTP device that is capable of adding, modifying, sending, and deleting VTP configuration information.

Ø  VTP transparent A device that does not participate in receiving or managing VTP domains, but will forward VTP information through its trunk ports.

CH14:

Ø  3DES Encryption algorithm supported by IPSEC.

Ø  AAA (Authentication, Authorization, and Accounting) A model designed by Cisco to enhance network security.

Ø  advanced encryption standard (AES) Encryption algorithm supported by IPSEC.

Ø  asymmetric key A form of encryption that uses a private and public key pair to encrypt and decrypt data.

Ø  authentication handler (AH). IPSec protocol that provides authentication services only by adding a header before the payload of an IP datagram.

Ø  authentication The process of users verifying to a directory services server on the network that they are who they say they are.

Ø  bastion host A computer built to withstand an attack.

Ø  boot-sector virus A virus that infects the master boot record of a computer.

Ø  client-to-site VPN A VPN that allows designated users to have access to the corporate network from remote locations (also known as remote user VPN).

Ø  DDoS Distributed Denial-of-Service attack. A denial-of-service attack launched by multiple affected computers. The attack is specifically aimed at flooding the destination’s available bandwidth.

Ø  demilitarized zone (DMZ) A firewall design that consists of having two packet filtering routers with a screened subnet available to the Internet.

Ø  dual-homed bastion A computer on the network that has two network cards in it. This computer is designed to withstand attacks from outside parties.

Ø  encapsulating security payload (ESP) IPSec protocol that supports encryption and authentication services if needed.

Ø  encryption The conversion or scrambling of data into a format readable only by descrambling it.

Ø  firewall A device used to permit or deny traffic between two security domains.

Ø  generic routing encapsulation (GRE) An unencrypted, Cisco proprietary tunneling protocol.

Ø  hacker An individual interested in stealing data or breaking into a network for malicious intent.

Ø  hashed message authentication code (HMAC) Secret key authentication algorithm that ensures data integrity and originality based on the distribution of the secret key.

Ø  internet key exchange (IKE) IPSec key management protocol.

Ø  internet security association and key management protocol (ISAKMP) The authority that governs IPSec key management.

Ø  intrusion detection systems (IDS) A network device that analyzes data packets to detect malicious behavior. An IDS is not installed inline with the network. Therefore it cannot take action on malicious data. However, it can report it.

Ø  intrusion prevention system (IPS) A network device that analyzes data packets to detect malicious behavior. An IPS is installed inline with the network and has the ability to drop packets that are malicious.

Ø  IPsec A suite of protocols that has been accepted as an industry standard and provides secure data transmission over layer 3 of the OSI model.

Ø  layer 2 tunneling protocol (L2TP) An extension of the point-to-point protocol used to create a secure tunnel for data to go through when remotely connecting to a network.

Ø  logic bomb A piece of code inserted into a program that will perform specific malicious functions when specified conditions are met.

Ø  macro virus A virus disguised as a macro for a specific application.

Ø  malware Malicious code that can infect a network. Types of malware include viruses, worms, Trojan horses, and logic bombs.

Ø  message-digest algorithm 5 (MD5) An authentication algorithm supported by IPSec.

Ø  packet-filtering router A router designed to examine data packets as they enter the network.

Ø  permissions Access rights given to a user to determine whether or not that user can access a resource.

Ø  physical security Physically securing your organization’s computer equipment and network devices.

Ø  point-to-point tunneling protocols (PPTP) A tunneling protocol that creates a secure tunnel for data to go through when remotely connecting to a network.

Ø  polymorphic virus A virus that changes its appearance (or signature) each time it replicates or infects.

Ø  RADIUS An industry standard authentication service that can be configured on Cisco devices.

Ø  secure shell (SSH) A cryptographic protocol that uses public key encryption to secure the communications channel between two hosts on the network.

Ø  secure sockets layer (SSL) A cryptographic protocol that provides secure communication for data that traverses a network.

Ø  security policy An organization’s set of rules around data management.

Ø  secure hash algorithm (SHA-1) An authentication algorithm supported by IPSec

Ø  single-homed bastion A computer built to withstand an attack. This computer has one network card installed in it and forwards all data to a firewall after inspecting it.

Ø  site-to-site VPN A VPN that allows multiple corporate sites to be connected together over low-cost Internet connections.

Ø  stealth virus A virus that attempts to hide itself from detection.

Ø  symmetric key Symmetric key encryption is a single-key encryption method enabling data to be encrypted and decrypted through the use of one key.

Ø  TACACS+ A proprietary authentication service that can be configured on Cisco devices.

Ø  transform set The configuration parameters in a Cisco firewall IPSEC VPN.

Ø  transport mode An IPSec mode that is primarily geared toward encrypting data that is being sent host-to-host. It only encrypts and decrypts the individual data packets. It does not provide tunneling services.

Ø  Trojan horse Malware that appears to perform a desired function but in fact performs malicious functions.

Ø  tunnel mode An IPSec mode that supports the secure tunneling of all data sent through it.

Ø  virus Malware that is used to steal or damage data. Requires user intervention to propagate.

Ø  virtual private network (VPN). VPNs provide for low-cost secure data connections between multiple sites. VPNs can be built as a site-to-site connection, remote user connections, and even between two separate companies’ networks (that have a common business requirement), which is considered an extranet.

Ø  worm Malware that once activated can replicate itself throughout the network by taking advantage of services on the computers in the network.