Term
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Definition
| The 10-Mbps baseband Ethernet specification using two pairs of twisted-pair cabling (Categories 3, 4, or 5): 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 100 m (328 feet) per segment. |
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Term
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Definition
| A name for the IEEE Fast Ethernet standard that uses two-pair copper cabling, a speed of 100 Mbps, and a maximum cable length of 100 meters. |
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Term
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Definition
| 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 meters. |
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Term
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Definition
| The IEEE standardized protocol for VLAN trunking. |
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Term
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Definition
| The IEEE standard for wireless LANs using the U-NII spectrum, OFDM encoding, at speeds of up to 54 Mbps. |
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Term
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Definition
| The IEEE standard for wireless LANs using the ISM spectrum, DSSS encoding, and speeds of up to 11 Mbps. |
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Term
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Definition
| The IEEE standard for wireless LANs using the ISM spectrum, OFDM or DSSS encoding, and speeds of up to 54 Mbps. |
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Term
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Definition
| The IEEE standard for wireless LAN security, including authentication and encryption. |
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Term
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Definition
| The IEEE standard for wireless LANs using ISM spectrum, OFDM encoding, multiple antennae, for single-stream speeds up to 150 Mbps. |
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Term
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Definition
| 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. |
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Term
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Definition
| A LAN network design term that refers to a switch interface connected to end-user devices. |
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Term
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Definition
| In Frame Relay, the physical serial link that connects a Frame Relay DTE device, usually a router, to a Frame Relay switch. The access link uses the same physical layer standards as do point-to-point leased lines. |
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Term
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Definition
| 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. |
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Term
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Definition
| In security, the recording of access attempts. See AAA. |
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Term
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Definition
| In wireless LANs, a method or mode of operation in which clients send data directly to each other without the use of a wireless access point (AP). |
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Term
| adjacent-layer interaction |
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Definition
| 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. |
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Term
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Definition
| In Cisco routers, a means for one router to choose 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. |
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Term
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Definition
| Asymmetric digital subscriber line. One of many DSL technologies, ADSL is designed to deliver more bandwidth downstream (from the central office to the customer site) than upstream. |
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Term
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Definition
| The term used by Cisco to refer to a variety of security tools that help prevent various attacks, including antivirus, anti-phishing, and anti-spam. |
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Term
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Definition
| Address Resolution Protocol. An Internet protocol used to map an IP address to a MAC address. Defined in RFC 826. |
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Term
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Definition
| 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. |
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Term
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Definition
| 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. |
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Term
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Definition
| Asynchronous Transfer Mode. The international standard for cell relay in which multiple service types (such as voice, video, and data) are conveyed in fixedlength (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. |
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Term
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Definition
| In security, the verification of the identity of a person or a process. |
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Term
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Definition
| In security, the determination of the rights allowed for a particular user or device. |
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Term
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Definition
| An internetwork in the administrative control of one organization, company, or governmental agency, inside which that organization typically runs an Interior Gateway Protocol (IGP). |
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Term
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Definition
| 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. |
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Term
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Definition
| link A serial link between two routers, created without CSU/DSUs, by connecting a DTE cable to one router and a DCE cable to the other. Typically used in labs to build serial links without the expense of an actual leased line from the telco. |
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Term
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Definition
| A term that refers to a general type of routing protocol algorithm, the other two being distance vector and link state. The Enhanced Interior Gateway Routing Protocol (EIGRP) is the only routing protocol that Cisco classifies as using a balanced hybrid algorithm. |
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Term
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Definition
| A reference to the speed of a networking link. Its origins come from earlier communications technology in which the range, or width, of the frequency band dictated how fast communications could occur. |
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Term
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Definition
| In wireless LANs, a WLAN with a single access point. |
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Term
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Definition
| 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. |
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Term
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Definition
| A math operation performed 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. |
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Term
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Definition
| The low-order 4 bits of the configuration 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. |
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Term
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Definition
| Basic Rate Interface. An ISDN interface composed of two 64-kbps bearer (B) channels and one 16-kbps data (D) channel for circuit-switched communication of voice, video, and data. |
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Term
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Definition
| 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. |
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Term
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Definition
| An Ethernet frame sent to destination address FFFF.FFFF.FFFF, meaning that the frame should be delivered to all hosts on that LAN. |
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Term
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Definition
| 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. |
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Term
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Definition
| 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. |
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Term
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Definition
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. |
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Term
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Definition
| A device on the other end of some communications cable that is advertising CDP updates. |
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Term
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Definition
| A generic reference to network services, typically WAN services, in which the provider sets up a (layer 1) circuit between two devices, and the provider makes no attempt to interpret the meaning of the bits. |
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Term
| Cisco Configuration Professional (CCP) |
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Definition
| A graphical web-based interface useful to configure Cisco devices, including routers and switches. CCP replaces Cisco Security Device Manager (SDM) has the preferred software to graphically configure Cisco routers and switches. |
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Term
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Definition
| An IPv4 Class A, B, or C network; called a classful network because these networks are defined by the class rules for IPv4 addressing. |
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Term
| classful routing protocol |
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Definition
| 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. Does not support VLSM. |
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Term
| classless routing protocol |
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Definition
| An inherent characteristic of a routing protocol, specifically that the routing protocol does 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. |
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Term
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Definition
| Command-line interface. An interface that enables the user to interact with the operating system by entering commands and optional arguments. |
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Term
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Definition
| The speed at which a serial link encodes bits on the transmission medium. |
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Term
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Definition
| The device to which the other devices on the link adjust their speed when using synchronous links. |
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Term
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Definition
| 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. |
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Term
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Definition
| 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. |
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Term
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Definition
| A set of network interface cards (NICs) 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. |
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Term
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Definition
| 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 (running-config). |
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Term
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Definition
| 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. |
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Term
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Definition
| 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. |
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Term
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Definition
| 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. |
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Term
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Definition
| 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. |
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Term
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Definition
| Customer premises equipment. Any equipment related to communications that is located at the customer site, as opposed to inside the telephone company’s network. |
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Term
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Definition
| An Ethernet cable that swaps the pair used for transmission on one device to a pair used for receiving on the device on the opposite end of the cable. In 10BASE-T and 100BASE-TX networks, this cable swaps the pair at pins 1,2 to pins 3,6 on the other end of the cable, and the pair at pins 3,6 to pins 1,2 as well. |
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Term
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Definition
| Carrier sense multiple access with collision avoidance. A media-access mechanism that defines how devices decide when they can send, with a goal of avoiding collisions as much as possible. IEEE WLANs use CSMA/CA. |
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Term
|
Definition
| Carrier sense multiple access collision detect. 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 retransmissions from those devices for some random length of time. |
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Term
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Definition
| 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. |
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Term
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Definition
| One of three options for internal processing on some models of Cisco LAN switches in which the frame is forwarded as soon as possible, including forwarding the first bits of the frame before the whole frame is received. |
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Term
|
Definition
| 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. |
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Term
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Definition
| (de-encapsulation) 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. |
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Term
| default gateway/default router |
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Definition
| On an IP host, the IP address of some router to which the host sends packets when the packet’s destination address is on a subnet other than the local subnet. |
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Term
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Definition
| 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 networks, and 255. 255. 255. 0 for Class C networks. |
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Term
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Definition
| On a router, the route that is considered to match all packets that are not otherwise matched by some more specific route. |
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Term
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Definition
| The legal term for the demarcation or separation point between the telco’s equipment and the customer’s equipment. |
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Term
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Definition
| 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. |
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Term
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Definition
| 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 addresses. |
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Term
| Direct Sequence Spread Spectrum (DSSS) |
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Definition
| A method of encoding data for transmission over a wireless LAN in which the device uses 1 of 11 (in the U. S. ) nearby frequencies in the 2. 4-GHz range. |
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Term
|
Definition
| 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 linkstate routing algorithms. |
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Term
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Definition
| Domain Name System. An application layer protocol used throughout the Internet for translating hostnames into their associated IP addresses. |
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Term
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Definition
| Digital signal level 0. A 64-kbps line or channel of a faster line inside a telco whose origins are to support a single voice call using the original voice (PCM) codecs. |
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Term
|
Definition
| Digital signal level 1. A 1. 544-Mbps line from the telco, with 24 DS0 channels of 64 kbps each, plus an 8-kbps management and framing channel. Also called a T1. |
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Term
|
Definition
| Digital subscriber line. Public network technology that delivers high bandwidth over conventional telco local-loop copper wiring at limited distances. Typically used as an Internet access technology, connecting a user to an ISP. |
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Term
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Definition
| Data terminal equipment. From a Layer 1 perspective, the DTE synchronizes its clock based on the clock sent by the DCE. From a packet-switching perspective, the DTE is the device outside the service provider’s network, typically a router. |
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Term
|
Definition
| Similar to a T1, but used in Europe. It uses a rate of 2. 048 Mbps and 32 64-kbps channels, with one channel reserved for framing and other overhead. |
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Term
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Definition
| A part of the Cisco IOS CLI in which the user can use the most powerful and potentially disruptive commands on a router or switch, including the ability to then reach configuration mode and reconfigure the router. |
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Term
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Definition
| The placement of data from a higher-layer protocol behind the header (and in some cases, between a header and trailer) of the next-lower-layer protocol. For example, an IP packet could be encapsulated in an Ethernet header and trailer before being sent over an Ethernet. |
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Term
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Definition
| Applying a specific algorithm to data to alter the appearance of the data, making it incomprehensible to those who are not authorized to see the information. |
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Term
|
Definition
| The process of discovering whether or not a data-link level frame was changed during transmission. This process typically uses a Frame Check Sequence (FCS) field in the data-link trailer. |
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Term
|
Definition
| An interface state on LAN switches that is the result of one of many security violations. |
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Term
|
Definition
| The process of noticing when some transmitted data was not successfully received and resending the data until it is successfully received. |
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Term
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Definition
| A series of LAN standards defined by the IEEE, originally invented by Xerox Corporation and developed jointly by Xerox, Intel, and Digital Equipment Corporation. |
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Term
| Extended Service Set (ESS) |
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Definition
| In wireless LANs, a WLAN with multiple access points to create one WLAN, allowing roaming between the APs. |
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Term
| Exterior Gateway Protocol (EGP) |
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Definition
| A routing protocol that was designed to exchange routing information between different autonomous systems. |
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Term
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Definition
| Generally, a process or a 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. |
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Term
|
Definition
| 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. |
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Term
|
Definition
| 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. |
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Term
|
Definition
| 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. Switches also forward multicasts by default, although this behavior can be changed. |
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Term
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Definition
| 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. |
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Term
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Definition
| To send a frame received in one interface out another interface, toward its ultimate destination. |
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Term
|
Definition
| 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. |
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Term
|
Definition
| A line from the telco with four wires, composed of two twistedpair wires. Each pair is used to send in one direction, so a four-wire circuit allows fullduplex communication. |
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Term
|
Definition
| One of three internal processing options on some Cisco LAN switches in which the first bits of the frame may 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. |
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Term
|
Definition
| A term referring to a data-link header and trailer, plus the data encapsulated between the header and trailer. |
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Term
|
Definition
| 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. |
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Term
| Frequency Hopping Spread Spectrum |
|
Definition
| 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. |
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Term
|
Definition
| 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. |
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Term
|
Definition
| A network topology in which more than two devices can physically communicate and, by choice, all pairs of devices are allowed to communicate directly. |
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Term
|
Definition
| Generically, any communication in which only one device at a time can send data. In Ethernet LANs, the normal result of the CSMA/CD algorithm that enforces the rule that only one device should send at any point in time. |
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Term
|
Definition
| High-Level Data Link Control. A bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization (ISO). |
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Term
|
Definition
| The upstream, transmit end of a cable TV (CATV) installation. |
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Term
|
Definition
| Any device that uses an IP address. |
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Term
|
Definition
| The IP address assigned to a network card on a computer. |
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Term
|
Definition
| A term used to describe a part of an IPv4 address that is used to uniquely identify a host inside a subnet. The host part is identified by the bits of value 0 in the subnet mask. |
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Term
|
Definition
| A route with a /32 mask, which by virtue of this mask represents a route to a single host IP address. |
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Term
|
Definition
| Hypertext Markup Language. A simple document-formatting language that uses tags to indicate how a given part of a document should be interpreted by a viewing application, such as a web browser. |
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Term
|
Definition
| Hypertext Transfer Protocol. The protocol used by web browsers and web servers to transfer files, such as text and graphic files. |
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Term
|
Definition
| A LAN device that provides a centralized connection point for LAN cabling, repeating any received electrical signal out all other ports, thereby creating a logical bus. Hubs do not interpret the electrical signals as a frame of bits, so hubs are considered to be Layer 1 devices. |
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Term
|
Definition
| Internet Control Message Protocol. A TCP/IP network layer protocol that reports errors and provides other information relevant to IP packet processing. |
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Term
|
Definition
| Institute of Electrical and Electronics Engineers. A professional organization that develops communications and network standards, among other activities. |
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Term
|
Definition
| An IEEE LAN protocol that specifies an implementation of the LLC sublayer of the data link layer. |
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Term
|
Definition
| A set of IEEE LAN protocols that specifies the many variations of what is known today as an Ethernet LAN. |
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Term
|
Definition
| For switch MAC address tables, a timer associated with each entry, which counts time upwards from 0 and is reset to 0 each time a switch receives a frame with the same MAC address. The entries with the largest timers can be removed to make space for additional MAC address table entries. |
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Term
|
Definition
| A mode of wireless LAN (WLAN) operation in which WLAN clients send and receive data with an access point (AP), which allows the clients to communicate with the wired infrastructure through the AP. Clients do not send data to each other directly; the AP must receive the data from one client, and then send the data to the other WLAN client. |
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Term
|
Definition
| For packets sent to and from a host that resides inside the trusted part of a network that uses NAT, a term referring to the IP address used in the headers of those packets when those packets traverse the global (public) Internet. |
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Term
|
Definition
| For packets sent to and from a host that resides inside the trusted part of a network that uses NAT, a term referring to the IP address used in the headers of those packets when those packets traverse the Enterprise (private) part of the network. |
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Term
interior routing protocol
aks interior gateway protocol (IGP) |
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Definition
| A routing protocol designed for use within a single organization. |
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Term
| intrusion detection system (IDS) |
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Definition
| A security function that examines more complex traffic patterns against a list of both known attack signatures and general characteristics of how attacks may be carried out, rating each perceived threat and reporting the threats. |
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Term
| intrusion prevention system (IPS) |
|
Definition
| A security function that examines more complex traffic patterns against a list of both known attack signatures and general characteristics of how attacks may be carried out, rating each perceived threat and reacting to prevent the more significant threats. |
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Term
|
Definition
| Cisco operating system software that provides the majority of a router’s or switch’s features, with the hardware providing the remaining features. |
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Term
|
Definition
| A file that contains the IOS. |
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Term
|
Definition
| Internet Protocol. The network layer protocol in the TCP/IP stack, providing routing and logical addressing standards and services. |
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Term
|
Definition
| In IP Version 4 (IPv4), a 32-bit address assigned to hosts using TCP/IP. Each address consists of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing, and the host number is used to address an individual host within the network or subnetwork. |
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Term
|
Definition
| Integrated Services Digital Network. A service offered by telephone companies that permits telephone networks to carry data, voice, and other traffic. Often used as an Internet access technology, as well as dial backup when routers lose their normal WAN communications links. |
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Term
|
Definition
| Inter-Switch Link. A Cisco-proprietary protocol that maintains VLAN information as traffic flows between switches and routers. |
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Term
|
Definition
| International Organization for Standardization. An international organization that is responsible for a wide range of standards, including many standards relevant to networking. The ISO developed the OSI reference model, a popular networking reference model. |
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Term
|
Definition
| 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. |
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Term
|
Definition
| The data compiled by a Layer 4 protocol, including Layer 4 headers and encapsulated high-layer data, but not including lower-layer headers and trailers. |
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Term
|
Definition
| A protocol that has characteristics like OSI Layer 3, which defines logical addressing and routing. IP, IPX, and AppleTalk DDP are all Layer 3 protocols. |
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Term
|
Definition
| The process used by switches for discovering MAC addresses, and their relative location, by looking at the source MAC address of all frames received by a bridge or switch. |
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Term
|
Definition
| A serial communications circuit between two points, provided by some service provider, typically a telephone company (telco). Because the telco does not sell a physical cable between the two endpoints, instead charging a monthly fee for the ability to send bits between the two sites, the service is considered to be a leased service. |
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Term
|
Definition
| A classification of the underlying algorithm used in some routing protocols. Link-state protocols build a detailed database that lists links (subnets) and their state (up, down), from which the best routes can then be calculated. |
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Term
|
Definition
| Logical Link Control. The higher of the two data link layer sublayers defined by the IEEE. Synonymous with IEEE 802. 2. |
|
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Term
|
Definition
| A line from the premises of a telephone subscriber to the telephone company CO. |
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Term
|
Definition
| A generic reference to addresses as defined by Layer 3 protocols, which do not have to be concerned with the physical details of the underlying physical media. Used mainly to contrast these addresses with data-link addresses, which are generically considered to be physical addresses because they differ based on the type of physical medium. |
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Term
|
Definition
| Media Access Control. The lower of the two sublayers of the data link layer defined by the IEEE. Synonymous with IEEE 802. 3 for Ethernet LANs. |
|
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Term
|
Definition
| A standardized data link layer address that is required for every device that connects to a LAN. Ethernet MAC addresses are 6 bytes long and are controlled by the IEEE. Also known as a hardware address, a MAC layer address, and a physical address. |
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Term
|
Definition
| A unit of measure used by routing protocol algorithms to determine the best route for traffic to use to reach a particular destination. |
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Term
|
Definition
| 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 interface. 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. |
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Term
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Definition
| Modulator-demodulator. A device that converts between digital and analog signals so that a computer may send data to another computer using analog telephone lines. At the source, a modem converts digital signals to a form suitable for transmission over analog communication facilities. At the destination, the analog signals are returned to their digital form. |
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Term
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Definition
| 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. |
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Term
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Definition
| A server connected to a network that resolves network names into network addresses. |
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Term
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Definition
| Network Address Translation. A mechanism for reducing the need for globally unique IP addresses. NAT allows an organization with addresses that are not globally unique to connect to the Internet by translating those addresses into public addresses in the globally routable address space. |
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Term
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Definition
| A collection of computers, printers, routers, switches, and other devices that can communicate with each other over some transmission medium. |
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Term
| network broadcast address |
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Definition
| In IPv4, a special address in each classful network that can be used to broadcast a packet to all hosts in that same classful network. |
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Term
network number
aka network address |
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Definition
| A number that uses dotted decimal notation like IP addresses, but the number itself represents all hosts in a single Class A, B, or C IP network. Numerically, the address has the same value as the network number in the network part of the address, and all 255s in the host octets—for example, 10. 255. 255. 255 is the network broadcast address for classful network 10. 0. 0. 0. |
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Term
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Definition
| The portion of an IPv4 address that is either 1, 2, or 3 octets/bytes long, based on whether the address is in a Class A, B, or C network. |
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Term
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Definition
| A generic term referring to any set of protocols and standards collected into a comprehensive grouping that, when followed by the devices in a network, allows all the devices to communicate. Examples include TCP/IP and OSI. |
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Term
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Definition
| Nonvolatile RAM. A type of random-access memory (RAM) that retains its contents when a unit is powered off. |
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Term
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Definition
| 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. |
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Term
| Orthogonal Frequency Division Multiplexing |
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Definition
| A method of encoding data in wireless LANs that allows for generally higher data rates than the earlier FHSS and DSSS encoding methods. |
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Term
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Definition
| 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. |
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Term
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Definition
| A logical grouping of information that includes the network layer header and encapsulated data, but specifically does not include any headers and trailers below the network layer. |
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Term
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Definition
| A generic reference to network services, typically WAN services, in which the service examines the contents of the transmitted data to make some type of forwarding decision. This term is mainly used to contrast with the WAN term circuit switching, in which the provider sets up a (Layer 1) circuit between two devices, and the provider makes no attempt to interpret the meaning of the bits. |
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Term
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Definition
| A network topology in which more than two devices could physically communicate but, by choice, only a subset of the pairs of devices connected to the network is allowed to communicate directly. |
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Term
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Definition
| Pulse code modulation. A technique of encoding analog voice into a 64-kbps data stream by sampling with 8-bit resolution at a rate of 8000 times per second. |
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Term
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Definition
| Protocol data unit. An OSI term to refer generically to a grouping of information by a particular layer of the OSI model. More specifically, an LxPDU would imply the data and headers as defined by Layer x. |
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Term
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Definition
| Packet Internet groper. An Internet Control Message Protocol (ICMP) echo message and its reply; ping often is used in IP networks to test the reachability of a network device. |
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Term
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Definition
| The documentation and implementation of which wires inside a cable connect to each pin position in any connector. |
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Term
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Definition
| In TCP and UDP, a number that is used to uniquely identify the application process that either sent (source port) or should receive (destination port) data. In LAN switching, another term for switch interface. |
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Term
| Port Address Translation (PAT) |
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Definition
| A NAT feature in which one inside global IP address supports over 65,000 concurrent TCP and UDP connections. |
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Term
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Definition
| A field in a TCP or UDP header that identifies the application that either sent (source port) or should receive (destination port) the data inside the data segment. |
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Term
| positive acknowledgment and retransmission (PAR) |
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Definition
| A generic reference to how the error recovery feature works in many protocols, including TCP, in which the receiver must send an acknowledgment that either implies that the data was (positively) received, or send an acknowledgment that implies that some data was lost, so the sender can then resend the lost data. |
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Term
| Power-on Self Test (POST) |
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Definition
| The process on any computer, including routers and switches, in which the computer hardware first runs diagnostics on the required hardware before even trying to load a bootstrap program. |
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Term
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Definition
| Point-to-Point Protocol. A protocol that provides router-to-router and host-tonetwork connections over synchronous point-to-point and asynchronous point-topoint circuits. |
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Term
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Definition
| A shorter way to write a subnet mask in which the number of binary 1s in the mask is simply written in decimal. For instance, /24 denotes the subnet mask with 24 binary 1 bits in the subnet mask. The number of bits of value binary 1 in the mask is considered to be the prefix length. |
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Term
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Definition
| Primary Rate Interface. An Integrated Services Digital Network (ISDN) interface to primary rate access. Primary rate access consists of a single 64-kbps D channel plus 23 (T1) or 30 (E1) B channels for voice or data. |
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Term
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Definition
IP addresses in several Class A, B, and C networks that are set aside for use inside private organizations. These addresses, as defined in RFC 1918, are not routable through the Internet. The address ranges are:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255 |
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Term
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Definition
| The part of the troubleshooting process in which the engineer attempts to rule out possible causes of the problem until the root cause of the problem can be identified. |
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Term
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Definition
| A generic term referring to the header defined by some layer of a networking model, and the data encapsulated by the header (and possibly trailer) of that layer, but specifically not including any lower-layer headers and trailers. |
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Term
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Definition
| A field in a LAN header that identifies the type of header that follows the LAN header. Includes the DIX Ethernet Type field, the IEEE 802. 2 DSAP field, and the SNAP protocol Type field. |
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Term
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Definition
| Public Switched Telephone Network. A general term referring to the variety of telephone networks and services in place worldwide. Sometimes called POTS, or Plain Old Telephone Service. |
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Term
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Definition
| Post, telephone, and telegraph. A government agency that provides telephone services. PTTs exist in most areas outside of North America and provide both local and long-distance telephone services. |
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Term
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Definition
| An IP address that is part of a registered network number, as assigned by an Internet Assigned Numbers Authority (IANA) member agency, so that only the organization to which the address is registered is allowed to use the address. Routers in the Internet should have routes allowing them to forward packets to all the publicly registered IP addresses. |
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Term
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Definition
| Random-access memory. A type of volatile memory that can be read and written by a microprocessor. |
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Term
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Definition
| Request For Comments. A document used as the primary means for communicating information about the TCP/IP protocols. Some RFCs are designated by the Internet Architecture Board (IAB) as Internet standards, and others are informational. RFCs are available online from numerous sources, including http:// www. rfc-editor. org/. |
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Term
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Definition
| Routing Information Protocol. An Interior Gateway Protocol (IGP) that uses distance vector logic and router hop count as the metric. RIP Version 1 (RIP-1) has become unpopular, with RIP Version 2 (RIP-2) providing more features, including support for VLSM. |
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Term
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Definition
| A popular type of cabling connector used for Ethernet cabling. It is similar to the RJ-11 connector used for telephone wiring in homes in the United States. RJ-45 allows the connection of eight wires. |
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Term
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Definition
| Read-only memory. A type of nonvolatile memory that can be read but not written by the microprocessor. |
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Term
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Definition
| A shorter name for ROM Monitor, which is a low-level operating system that can be loaded into Cisco routers for several seldom needed maintenance tasks, including password recovery and loading a new IOS when Flash memory has been corrupted. |
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Term
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Definition
| A troubleshooting term that refers to the reason why a problem exists, specifically a reason for which, if changed, the problem would either be solved or changed to a different problem. |
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Term
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Definition
| A protocol which defines packets that can be routed by a router. Examples of routed protocols include AppleTalk, DECnet, and IP. |
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Term
| Router Security Device Manager |
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Definition
| The administrative web-based interface on a router that allows for configuration and monitoring of the router, including the configuration of DHCP and NAT/PAT. |
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Term
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Definition
| A set of messages and processes with which routers can exchange information about routes to reach subnets in a particular network. Examples of routing protocols include the Enhanced Interior Gateway Routing Protocol (EIGRP), the Open Shortest Path First (OSPF) protocol, and the Routing Information Protocol (RIP). |
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Term
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Definition
| A list of routes in a router, with each route listing the destination subnet and mask, the router interface out which to forward packets destined to that subnet, and, as needed, the next-hop router’s IP address. |
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Term
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Definition
| A generic reference to any routing protocol’s messages in which it sends routing information to a neighbor. |
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Term
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Definition
| file In Cisco IOS switches and routers, the name of the file that resides in RAM memory, holding the device’s currently used configuration. |
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Term
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Definition
| A limited-function version of IOS stored in ROM in some older models of Cisco routers, for the purpose of performing some seldom needed low-level functions, including loading a new IOS into Flash memory when Flash has been deleted or corrupted. |
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Term
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Definition
| The communication between two networking devices for the purposes of the functions defined at a particular layer of a networking model, with that communication happening by using a header defined by that layer of the model. The two devices set values in the header, send the header and encapsulated data, with the receiving device(s) interpreting the header to decide what action to take. |
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Term
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Definition
| A TCP/IP application layer protocol that supports terminal emulation between a client and server, using dynamic key exchange and encryption to keep the communications private. |
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Term
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Definition
| In TCP, a term used to describe a TCP header and its encapsulated data (also called an L4PDU). Also in TCP, the process of accepting a large chunk of data from the application layer and breaking it into smaller pieces that fit into TCP segments. In Ethernet, a segment is either a single Ethernet cable or a single collision domain (no matter how many cables are used). |
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Term
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Definition
| The process of breaking a large piece of data from an application into pieces appropriate in size to be sent through the network. |
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Term
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Definition
| A type of cable with many different styles of connectors used to connect a router to an external CSU/DSU on a leased-line installation. |
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Term
| Service Set Identifier (SSID) |
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Definition
| A text value used in wireless LANs to uniquely identify a single WLAN. |
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Term
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Definition
| An option on Cisco IOS switches and routers that prompts the user for basic configuration information, resulting in new running-config and startup-config files. |
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Term
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Definition
| An Ethernet that uses a hub, or even the original coaxial cabling, which results in the devices having to take turns sending data, sharing the available bandwidth. |
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Term
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Definition
| A type of fiber-optic cabling with a narrow core that allows light to enter only at a single angle. Such cabling has a higher bandwidth than multimode fiber but requires a light source with a narrow spectral width (such as a laser). |
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Term
|
Definition
| For protocols such as TCP that allow the receiving device to dictate the amount of data the sender can send before receiving an acknowledgment—a concept called a window—a reference to the fact that the mechanism to grant future windows is typically just a number that grows upwards slowly after each acknowledgment, sliding upward. |
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Term
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Definition
| Synchronous Optical Network. A standard format for transporting a wide range of digital telecommunications services over optical fiber. |
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Term
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Definition
| A bridge protocol that uses the Spanning Tree algorithm, allowing a switch to dynamically work around loops in a network topology by creating a spanning tree. Switches exchange bridge protocol data unit (BPDU) messages with other bridges to detect loops and then remove the loops by shutting down selected bridge interfaces. |
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Term
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Definition
| A network topology in which endpoints on a network are connected to a common central device by point-to-point links. |
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Term
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Definition
| In Cisco IOS switches and routers, the name of the file that resides in NVRAM memory, holding the device’s configuration that will be loaded into RAM as the running-config file when the device is next reloaded or powered on. |
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Term
| store-and-forward switching |
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Definition
| One of three internal processing options on some Cisco LAN switches in which the Ethernet frame must be completely received before the switch can begin forwarding the first bit of the frame. |
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Term
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Definition
| Shielded twisted pair. Shielded twisted-pair cabling has a layer of shielded insulation to reduce electromagnetic interference (EMI). |
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Term
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Definition
| In Ethernet, a cable that connects the wire on pin 1 on one end of the cable to pin 1 on the other end of the cable, pin 2 on one end to pin 2 on the other end, and so on. |
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Term
|
Definition
| Subdivisions of a Class A, B, or C network, as configured by a network administrator. Subnets allow a single Class A, B, or C network to be used instead of multiple networks, and still allow for a large number of groups of IP addresses, as is required for efficient IP routing. |
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Term
subnet address
aka subnet number |
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Definition
| In IP v4, a dotted decimal number that represents all addresses in a single subnet. Numerically, the smallest value in the range of numbers in a subnet, reserved so that it cannot be used as a unicast IP address by a host. |
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Term
|
Definition
| A special address in each subnet, specifically the largest numeric address in the subnet, designed so that packets sent to this address should be delivered to all hosts in that subnet. |
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Term
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Definition
| A 32-bit number that numerically describes the format of an IP address by representing the combined network and subnet bits in the address with mask bit values of 1, and representing the host bits in the address with mask bit values of 0. |
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Term
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Definition
| In a subnetted IPv4 address, interpreted with classful addressing rules, one of three parts of the structure of an IP address, with the subnet part uniquely identifying different subnets of a classful IP network. |
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Term
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Definition
| The process of subdividing a Class A, B, or C network into smaller groups called subnets. |
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Term
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Definition
| A network device that filters, forwards, and floods Ethernet frames based on the destination address of each frame. |
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Term
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Definition
| An Ethernet that uses a switch, and particularly not a hub, so that the devices connected to one switch port do not have to contend to use the bandwidth available on another port. This term contrasts with shared Ethernet, in which the devices must share bandwidth, whereas switched Ethernet provides much more capacity, as the devices do not have to share the available bandwidth. |
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Term
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Definition
| A feature of many Internet access technologies in which the downstream transmission rate is the same as the upstream transmission rate. |
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Term
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Definition
| The imposition of time ordering on a bit stream. Practically, a device will try to use the same speed as another device on the other end of a serial link. However, by examining transitions between voltage states on the link, the device can notice slight variations in the speed on each end and can adjust its speed accordingly. |
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Term
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Definition
| A line from the telco that allows transmission of data at 1. 544 Mbps, with the ability to treat the line as 24 different 64-kbps DS0 channels (plus 8 kbps of overhead). |
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Term
|
Definition
| Transmission Control Protocol. A connection-oriented transport layer TCP/IP protocol that provides reliable data transmission. |
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Term
|
Definition
| Transmission Control Protocol/Internet Protocol. A common name for the suite of protocols developed by the U. S. Department of Defense in the 1970s to support the construction of worldwide internetworks.TCP and IP are the two best-known protocols in the suite. |
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Term
|
Definition
| A common abbreviation for telephone company. |
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Term
|
Definition
| The standard terminal-emulation application layer protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log in to remote systems and use resources as if they were connected to a local system. Telnet is defined in RFC 854. |
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Term
|
Definition
| Short for traceroute. A program available on many systems that traces the path that a packet takes to a destination. It is used mostly to debug routing problems between hosts. |
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Term
|
Definition
| The name of a networking device that was a precursor to modern LAN switches. Bridges forward frames between LAN segments based on the destination MAC address. Transparent bridging is so named because the presence of bridges is transparent to network end nodes. |
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Term
|
Definition
| On a LAN switch, an interface that is currently using either 802. 1Q or ISL trunking. trunking Also called VLAN trunking. A method (using either the Cisco ISL protocol or the IEEE 802. 1q protocol) to support multiple VLANs that have members on more than one switch. |
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Term
|
Definition
| Transmission medium consisting of two insulated wires, with the wires twisted around each other in a spiral. An electrical circuit flows over the wire pair, with the current in opposite directions on each wire, which significantly reduces the interference between the two wires. |
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Term
|
Definition
| User Datagram Protocol. Connectionless transport layer protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams without acknowledgments or guaranteed delivery. |
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Term
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Definition
| An Ethernet frame whose destination MAC address is not listed in a switch’s MAC address table, so the switch must flood the frame. |
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Term
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Definition
| Jargon referring to the two interface states on a Cisco IOS router or switch (line status and protocol status), with the first “up” referring to the line status, and the second “up” referring to the protocol status. An interface in this state should be able to pass data-link frames. |
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Term
|
Definition
| A timer used by a router to indicate when to send the next routing update. |
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Term
|
Definition
| Universal Resource Locator. A standard for how to refer to any piece of information retrievable via a TCP/IP network, most notably used to identify web pages. For example, http://www. cisco. com/univercd is a URL that identifies the protocol (HTTP), hostname (www. cisco. com), and web page (/univercd). |
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Term
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Definition
| A mode of the user interface to a router or switch in which the user can type only nondisruptive EXEC commands, generally just to look at the current status, but not to change any operational settings. |
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Term
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Definition
| Unshielded twisted pair. A type of cabling, standardized by the Electronics Industry Alliance (EIA) and Telecommunications Industry Association (TIA), that holds twisted pairs of copper wires (typically four pair), and does not contain any shielding from outside interference. |
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Term
| variable-length subnet masks (VLSM) |
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Definition
| The capability to specify a different subnet mask for the same Class A, B, or C network number on different subnets. VLSM can help optimize available address space. |
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Term
|
Definition
| In packet-switched services like Frame Relay, VC refers to the ability of two DTE devices (typically routers) to send and receive data directly to each other, which supplies the same function as a physical leased line (leased circuit), but doing so without a physical circuit. This term is meant as a contrast with a leased line or leased circuit. |
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Term
|
Definition
| A group of devices, connected to one or more switches, with the devices grouped into a single broadcast domain through switch configuration. VLANs allow switch administrators to separate the devices connected to the switches into separate VLANs without requiring separate physical switches, gaining design advantages of separating the traffic without the expense of buying additional hardware. |
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Term
| virtual private network (VPN) |
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Definition
| The process of securing communication between two devices whose packets pass over some public and unsecured network, typically the Internet. VPNs encrypt packets so that the communication is private and authenticate the identity of the endpoints. |
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Term
|
Definition
| Voice over IP. The transport of voice traffic inside IP packets over an IP network. |
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Term
|
Definition
| Software, running on some computer, that stores web pages and sends those web pages to web clients (web browsers) that request the web pages. |
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Term
|
Definition
| A TCP or UDP port number reserved for use by a particular application. The use of well-known ports allows a client to send a TCP or UDP segment to a server, to the correct destination port for that application. |
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Term
|
Definition
| An organization formed by many companies in the wireless industry (an industry association) for the purpose of getting multivendor certified-compatible wireless products to market in a more timely fashion than would be possible by simply relying on standardization processes. |
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Term
| Wi-Fi Protected Access (WPA) |
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Definition
| A trademarked name of the Wi-Fi Alliance that represents a set of security specifications that predated the standardization of the IEEE 802. 11i security standard. |
|
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Term
|
Definition
| The term window represents the number of bytes that can be sent without receiving an acknowledgment. |
|
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Term
| wired equivalent privacy (WEP) |
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Definition
| An early WLAN security specification that used relatively weak security mechanisms, using only preshared keys and either no encryption or weak encryption. |
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Term
|
Definition
| A wireless device that wants to gain access to a wireless access point for the purpose of communicating with other wireless devices or other devices connected to the wired internetwork. |
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Term
|
Definition
| The Wi-Fi Alliance trademarked name for the same set of security specifications defined in the IEEE 802. 11i security standard. |
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Term
|
Definition
| 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. |
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