Vocabulary Flashcards
10BASE-T
The 10-Mbps baseband Ethernet specification using two pairs of twisted pair cabling (CAT III IV or V). One pair transmits data and the other receives data. 10BASE-T, which is part of the IEEE 802.3 specification, has a distance limit of approximately 100m per segment.
100BASE-T
A name for the IEEE Fast Ethernet standard that used two-pair copper cabling, a speed of 100 Mbps, and a maximum cable length of 100 m.
1000BASE-T
A name for the IEEE Gigabit Ethernet standard that uses four-pair copper cabling, a speed of 1000 Mbps (1 Gbps), and a maximum cable length of 100 m.
802.1Q
The IEEE standardized protocol for VLAN trunking.
802.11a
The IEEE standard for wireless LANs using the U-NII spectrum, OFDM encoding, at speeds up to 54 Mbps
802.11b
The IEEE standard for wireless LANs using the ISM spectrum, DSSS encoding, and speeds up to 11 Mbps
802.11g
The IEEE standard for wireless LANs using the ISM spectrum, OFDM or DSSS encoding and speeds of up to 54 Mbps.
802.11n
The IEEE standard for wireless LANs using the ISM spectrum, OFDM encoding, and multiple antennas for single-stream speeds up to 150 Mbps.
AAA
Authentication, authorization and accounting. Authentication confirms the identity of the user or device. Authorization determines what the user or device is allowed to do. Accounting records information about access attempts, including inappropriate requests.
Access Interface
A LAN network design term that refers to a switch interface connected to end-user devices, configured so that it does not use VLAN trunking.
Access Link
In Frame Relay, the physical serial link that connects a Frame Relay DTE device, usaully at router, to a Frame Relay switch. The access link uses the same physical layer standards as do point-to-point leased lines.
Access Point
a wireless LAN device that provides a means for wireless clients to send data to each other and to the rest of a wired network, with the AP connecting to both the wireless LAN and the wired Ethernet LAN.
Accounting
In security, the recording of access attempts. See AAA.
Address Block
In both IPv4 and IPv6, a set of consecutive addresses. This term is typically used for public addresses, assigned by some numbering authority (IANA/ICANN, an RIR, or an ISP).
Adjacent-Layer Interaction
The general topic of how on one computer, two adjacent layers in a networking architectural model work together, with the lower layer providing services to the higher layer.
Administrative Distance
In Cisco routers, a means for one router to chose between multiple routes to reach the same subnet when those routes were learned by different routing protocols. The lower the administrative distance, the better the source of the routing information.
ADSL
Asymmetric digital subscriber line. One of many DSL technologies, ADSL is designed to deliver more bandwidth down-stream (from the central office to the customer site) than upstream.
All-Nodes Multicast Address
A specific IPv6 multicast address, FF02::1, with link-local scope, used to send packets to all devices on the link that support IPv6.
All-Routers Mulitcast Address
A specific IPv6 multicast address, FF02::2, with a link-local scope, used to send packets to all devices that act as IPv6 routers on the local link.
Anti-X
The term used by Cisco to refer to a variety of security tools that help prevent various attacks, including antivirus, antiphishing, and antispam.
Area Border Router (ABR)
A router using OSPF in which the router has interfaces in multiple OSPF areas
ARP
Address Resolution Protocol. An Internet protocol used to map an IP address to a MAC address. Defined in RFC 826.
ARP table
A list of IP addresses of neighbors on the same VLAN, along with their MAC addresses, as kept in memory by hosts and routers.
ARPANET
The first packet-switched network, first created around 1970, which served as the predecessor to the Internet.
Asymmetric
A feature of many Internet access technologies, including DSL, cable, and modems, in which the downstream transmission rate is higher than the upstream transmission rate.
Asynchronous
The lack of an imposed time ordering on a bit stream. Practically, both sides agree to the same speed, but there is no check or adjustment of the rates if they are slightly different. However, because only 1 byte per transfer is sent, slight differences in clock speed are not an issue.
ATM
Asynchronous Transfer Mode. The international standard for cell relay in which multiple service types (such as voice, video and data) are conveyed in fixed length (53-byte cells). Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays.
Autonegotiation
An IEEE standard mechanism (802.3u) with which two nodes can exchange messages for the purpose of choosing to use the same Ethernet standards on both ends of the link, ensuring that the link functions and functions well.
Autonomous System
An internetwork in the administrative control of one organization, company, or governmental agency, inside which that organization typically runs an interior gateway protocol.
Auxiliary Port
A physical connector on a router that is designed to be used to allow a remote terminal, or PC with a terminal emulator, to access a router using an analog modem.
Back to Back Link
A serial link between two routers, created without CSU/DSUs, by connecting a DTE cable to one router and DCE cable to the other. Typically used in labs to build serial links without the expense of an actual leased line from the telco.
Balanced Hybrid
A term that, over the years, has been used to refer to the logic behind the EIGRP routing protocol. More commonly today, this logic is referred to as advanced distance vector logic.
Bandwidth
A reference to the speed of a networking link.
Basic Services Set (BSS)
In wireless LANs, a WLAN with a single access point.
bitwise Boolean AND
A Boolean AND between two numbers of the same length in which the first bit in each number is ANDed, and then the second bit in each number, and then the third, and so on.
Boolean AND
A math operation performced on a pair of one-digit binary numbers. The result is another one-digit binary number. 1 AND 1 yields 1; all other combinations yield a 0.
Boot Field
The low-order 4 bits of the configuraiton register in a Cisco router. The value in the boot field in part tells the router where to look for a Cisco IOS image to load.
Broadcast Address
Generally, any address that represents all devices, and can be used to send one message to all devices. In Ethernet, the MAC address of all binary 1s, or FFFF.FFFF.FFFF in hex. For IPv4, see subnet broadcast address.
Broadcast Domain
A set of all devices that receive broadcast frames originating from any device within the set. Devices in the same VLAN are in the same broadcast domain.
Broadcast Frame
An Ethernet frame sent to destination address FFFF.FFFF.FFFF, meaning that the frame should be delivered to all hosts on that LAN.
Broadcast Subnet
When subnetting a Class A, B, or C network, the one subnet in each classful network for which all subnet bits have a value of binary 1. The subnet broadcast address in this subnet has the same numeric value as the classful network’s network-wide broadcast address.
Bus
A common physical signal path composed of wires or other media across which signals can be sent from one part of a computer to another.
Cable Internet
An Internet access technology that uses a cable TV (CATV) cable, normally used for video, to send and receive data.
CDP
Cisco Discovery Protocol. A media- and protocol-independent device-discovery protocol that runs on most Cisco-manufactured equipment, including routers, access servers, and switches. Using CDP, a device can advertise its existence to other devices and receive information about other devices on the same LAN or on the remote side of a WAN.
CDP Neighbor
A device con the other end of some communications cable is advertising CDP updates.
CIDR
Classless interdomain routing. An RFC-standard tool for global IP address range assignment. CIDR reduces the size of Internet routers’ IP routing tables, helping deal with the rapid growth of the Internet. The term classless refers to the fac tthat the summarized groups of networks represent a group of addresses that do not conform to IPv4 classful (Class A, B, and C) grouping rules.
Circuit Switching
A generic reference to network servies, typically WAN services, in which the provider sets up a (Layer 1) circuit between two devices.
Cisco Express Forwarding (CEF)
A method of internal processing on Cisco routers, meant to make the routing process very efficient, doing so by caching IP routes in a table that can be searched very quickly, and by remembering data link headers rather than building them for every packet that is forwarded.
Classful IP Network
An IPv4 Class A, B, or C network; called a classful network because these networks are defined by the class rules for IPv4 addressing.
Classful Routing Protocol
Does not transmit the mask information along with the subnet number, and therefore must consider Class A,B, and C network boundaries and perform autosummarization at those boundaries.
Classless Routing Protocol
An inherent characteristic of a routing protocol, specifically that the routing protocol does not send subnet masks in its routing updates, thereby removing any need to make assumptions about the addresses in a particular subnet or network, making it able to support VLSM and manual route summarization.
CLI
Command-line interface. An interface that enables the user to interact with the operating system by entering commands and optional arguments.
Clock Rate
The speed at which a serial link encodes bits on the transmission medium.
Clock Source
The device to which the other devices on the link adjust their speed when using synchronous links.
Clocking
The process of supplying a signal over a cable, either on a separate pin on a serial cable or as part of the signal transitions in the transmitted signal, so that the receiving device can keep synchronization with the sending device.
Codec
Coder-decoder. An integrated circuit device that transforms analog voice signals into a digital bit stream and then transforms digital signals back into analog voice signals.
Collision Domain
A set of network interface cards (NIC) for which a frame sent by one NIC could result in a collision with a frame sent by any other NIC in the same collision domain.
Configuration Mode
A part of the Cisco IOS Software CLI in which the user can type configuration commands that are then added to the device’s currently used configuration file.
Configuration Register
In Cisco routers, a 16-bit, user configurable value that determines how the router functions during initialization. In software, the bit position is set by specifying a hexadecimal value using configuration commands.
Connected
The single-item status code listed by a switch SHOW INTERFACES STATUS command, with this status referring to a working interface.
Connected Route
On a router, an IP route added to the routing table when the router interface is both up and has an IP address configured. The route is for the subnet that can be calculated based on the configured IP address and mask.
Connection Establishment
The process by which a connection-oriented protocol creates a connection. With TCP, a connection is established by a three-way transmission of TCP segments.
Console Port
A physical socket on a router or switch to which a cable can be connected between a computer and the router/switch, for the purpose of allowing the computer to use a terminal emulator and use the CLI to configure, verify, and troubleshoot the router/switch.
Convergence
The time required for routing protocols to react to changes in the network, removing bad routes and adding new, better routes so that the current best routes are in all the routers’ routing tables.
CPE
Customer premises equipment. Any equipment related to communications that is located at the customer site, as opposed to inside the telephone company’s network.
Crossover Cable
An Ethernet cable that swaps TX and RX. Switches pins 1,2 to 3,6
CSMA/CD
Carrier sense mulitple access with collision detection. A media-access mechanism in which devices ready to transmit data first check the channel for a carrier. If no carrier is sensed for a specific period of time, a device can transmit. If two devices transmit at once, a collision occurs and is detected by all colliding devices. This collision subsequently delays re-transmissions from those devices for some random length of time.
CSU/DSU
Channel service unit/data service unit. A device that understands the Layer 1 details of serial links installed by a telco and how to use a serial cable to communicate with networking equipment such as routers.
Cut-Through Switching
One of three options for internal processing on some models of Cisco LAN switches in which the frame is forwarded as soon as enough of the Ethernet header has been received for the switch to make a forwarding decision, including forwarding the first bits of the frame before the whole frame is received.
keepalive
A proprietary feature of Cisco routers in which the router sends messages on a periodic basis as a means of letting the neighboring router know that the first router is still alive and well.
Quartet
A term used in this book, but not in other references, to refer to a set of four hex digits in an IPv6 address.
Zero Subnet
For every classful IPv4 network that is subnetted, the one subnet whose subnet number has all binary 0s in the subnet part of the number. In decimal, the zero subnet can be easily identified because it is the same number as the classful network number.
MAC
Media Access Control. The lower of the two sub layers of the data link layer defined by the IEEE. Synonymous with the IEEE 802.3 for Ethernet LANs.
MAC address
A standardized data link layer address that is required for every device that connects to a LAN. Ethernet MAC addressess are 6 bytes long and are controlled by the IEEE. Aka hardware address, physical address, and MAC layer address.
metric
A unit of measure used by routing protocol algorithms to determine the best route for traffic to use to reach a particular destination.
Microsegmentation
The process in LAN design by which every switch port connects to a single device, with no hubs connected to the switch ports, creating a separate collision domain per interference. The term’s origin relates to the fact that one definition for the word “segment” is “collision domain”, with a switch separating each switch port into a separate collision domain or segment.
Modem
Modulator-demodulator. A device that converts between digital and analog signals so that a computer can send data to another computer using analog telephone lines. At the source, a modem converts digital signals to form suitable for transmission over analog communication facilities. At the destination, the analog signals are returned to their digital form.
Multi-layer Switch
A LAN switch that can also perform Layer 3 routing functions. The name comes from the fact that this device makes forwarding decisions based on logic from multiple OSI layers (Layers 2 and 3).
Multimode
A type of fiber-optic cabling with a larger core than single-mode cabling, allowing light to enter at multiple angles. Such cabling has lower bandwidth than single-mode fiber but requires a typically cheaper light source, such as an LED rather than a laser.
Gigabit Ethernet
The common name for all the IEEE standards that send data at 1 gigabit per second.
Global Routing Prefix
An IPv6 prefix that defines an IPv6 address block made up of global unicast addresses, assigned to one organization, so that the organization has a block of globally uniqure IPv6 addresses to use in its network.
Global Unicast Address
A type of unicast IPv6 address that has been allocated from a range of public globally unique IP addresses, as registered through IANA/ICANN, its member agencies, and other registries or ISPs.
Ordered Data Transfer
A networking function, included in TCP, in which the protocol defines how the sending host should number the data transmitted, defines how the receiving device should attempt to reorder the data if it arrives out of order, and specifies to discard the data if it cannot be delivered in order.
OSI
Open System Interconnection reference model. A network architectural model developed by the ISO. The model consists of seven layers, each of which specifies particular network functions, such as addressing, flow control, error control, encapsulation, and reliable message transfer.
OSPF
Open Shortest Path First. A popular link-state IGP that uses a link-state database and the Shortest Path First (SPF) algorithm to calculate the best routes to reach each known subnet.
OSPF version 2
The version of the OSPF routing protocol that supports IPv4, and not IPv6, and has been commonly used for over 20 years.
OSPF version 3
The version of the OSPF routing protocol that supports IPv6, and not IPv4.
Outgoing Interface
In an IP route in a routing table, part of a routing table entry that refers to the local interface out which the local router should forward packets that match the route.
Overlapping Subnets
An (incorrect) IP subnet design condition in which one subnet’s range of addresses includes addresses in the range of another subnet.
Fast Ethernet
The common name for all the IEEE standards that send data at 100 Mbps.
Filter
Generally, a process or device that screens network traffic for certain characteristics, such as source address, destination address, or protocol, and determines whether to forward or discard that traffic based on the established criteria.
Firewall
A device that forwards packets between the less secure and more secure parts of the network, applying rules that determine which packets are allowed to pass, and which are not.
flash
A type of read/write permanent memory that retains its contents even with no power applied to the memory, and uses no moving parts, making the memory less likely to fail over time.
Flooding
The result of the LAN switch forwarding process for broadcasts and unknown unicast frames. Switches forward these frames out all interfaces, except the interface in which the frame arrived. Swithces also flood multicasts by default, although this behavior can be changed.
flow control
The process of regulating the amount of data sent by a sending computer toward a receiving computer. Several flow control mechanisms exist, including TCP flow control, which uses windowing.
forward
To send a frame received in one interface out another interface, toward its ultimate dimension.
forward acknowledgment
A process used by protocols that do error recovery, in which the number that acknowledges data lists the next data that should be sent, not the last data that was successfully received.
four-wire circuit
A line from the telco with four wires, composed of two twisted pair wires. Each pair is used to send in one direction, so a four-wire circuit allows full-duplex communication.
fragment-free switching
One of the three internal processing options on some Cisco LAN switches in which the first bits of the frame can be forwarded before the entire frame is received, but not until the first 64 bytes of the frame are received, in which case, in a well-designed LAN, collision fragments should not occur as a result of this forwarding logic.
frame
A term referring to a data link header and trailer, plus the data encapsulated between the header and trailer.
Frame Check Sequence
A field in many data link trailers used as part of the error-detection process.
Frame Relay
An international standard data link protocol that defines the capabilities to create a frame-switched (packet-switched) service, allowing DTE devices (typically routers) to send data to many other devices using a single physical connection to the Frame Relay service.
Frequency Hopping Spread Spectrum
A method of encoding data on a wireless LAN in which consecutive transmissions occur on different nearby frequency bands as compared with the prior transmission. Not used in modern WLAN standards.
full-duplex
Generically, any communication in which two communicating devices can concurrently send and receive data. In Ethernet LANs, the allowance for both devices to send and receive at the same time, allowed when both devices disable their CSMA/CD logic.
full mesh
A network topology in which more than two devices can physically communicate and, by choice, all pairs of devices are allowed to communicate directly.
DCE
Data communications equipment. From a physical layer perspective, the device providing the clocking on a WAN link, typically a CSU/DSU, is the DCE. From a packet-switching perspective, the service provider’s switch, to which a router might connect, is considered the DCE
deencapsulation
On a computer that receives data over a network, the process in which the device interprets the lower-layer headers, and, when finished with each header, removes the header, revealing the next-higher-layer PDU (protocol data unit).
default gateway/default router
On an IP host the IP address of some router to which the host sends packets when the packets destination address is on a subnet other than the local subnet.
default mask
The mask used in a Class A,B or C network that does not create any subnets; specifically, mask 255.0.0.0 for class A networks; 255.255.0.0 for Class B and 255.255.255.0 for class C networks
default route
On a router, the route that is considered to match all packets that are not otherwise matched by some more specific route.
demarc
The legal term for the demarcation or separation point between the telco’s equipment and the customer’s equipment
denial of service (DoS)
A type of attack whose goal is to cause problems by preventing legitimate users from being able to access services, thereby preventing the normal operation of computers and networks.
DHCP
Dynamic Host Configuration Protocol. A protocol used by hosts to dynamically discover and lease an IP address, and learn the correct subnet mask, default gateway and DNS server IP address.
DHCP Client
Any device that uses DHCP protocols to ask to lease an IP address from a DHCP server, or to learn any IP settings from that server.
DHCP Relay
The name of the router IOS feature that forwards DHCP messages from client to servers by changing the destination IP address from 255.255.255.255 to the IP address of the DHCP server.
DHCP Server
Software that waits for DHCP clients to request to lease IP addresses, with the server assigning a lease of an IP address as well as listing other important IP settings for the client.
distance vector
The logic behind the behavior of some interior routing protocols, such as RIP. Distance vector routing algorithms call for each router to send its entire routing table in each update, but only to its neighbors. Distance vector routing algorithms can be prone to routing loops but are computationally simpler than link-state routing algorithms.
DNS
Domain Name System. An application layer protocol used throughout the Internet for translating host names into their associated IP addresses.
