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Appendix D - Glossary

Cisco & IP Addressing
Louis D. Rossi, Louis R. Rossi and Thomas Rossi
  Copyright © 1999 The McGraw-Hill Companies, Inc.

Appendix D: Glossary
access control list  A list defining the kinds of access granted or denied to users of an object.
address     In data communication, this is a designated identifier.
address class     Traditional method of assigning blocks of addresses to organizations.
address mask    A bit mask used to select bits from an IP address for subnet addressing.
address resolution    Conversion of an IP address into a corresponding physical address, such as ETHERNET or token ring.
address resolution protocol (ARP)    A TCP/IP protocol used to dynamically bind a high-level IP address to low-level physical hardware addresses. ARP works across single physical networks and is limited to networks that support hardware broadcast.
address space    Addresses used to uniquely identify network-accessible units, sessions, adjacent link stations, and links in a node for each network in which the node participates.
addressing    In data communication, the way in which a station selects the station to which it is to send data. An identifiable place.
AppleTalk    A networking protocol developed by Apple Computer for use with its products.
application layer    According to the ISO OSI model, this is layer 7. It provides application services.
ARPANET    The world’s first packet-switching network. For many years it functioned as an Internet backbone.
autonomous system (AS)    An internetwork that is part of the Internet and has a single routing policy. Each Autonomous System is assigned an Autonomous System Number.
bandwidth    The quantity of data that can be sent across a link, typically measured in bits per second.
baud    A unit of signaling speed equal to the number of times per second that a signal changes state. If there are exactly two states, the baud rate equals the bit rate.
carrier-sense multiple access with collision detection (CSMA/CD)    A protocol utilizing equipment capable of detecting a carrier which permits multiple access to a common medium. This protocol also has the ability to detect a collision, because this type of technology is broadcast-oriented.
classless inter-domain routing (CIDR)    A method of routing used to enable the network part of IP addresses to consist of a specified number of bits.
collision    An event in which two or more devices simultaneously perform a broadcast on the same medium. This term is used in ETHERNET networks, and also in networks where broadcast technology is implemented.
collision detection    Term used to define a device that can determine when a simultaneous transmission attempt has been made.
congestion    A network state caused by one or more overloaded network devices. Congestion leads to datagram loss.
connected    To have a physical path from one point to another.
connection    A logical communication path between TCP users.
connection-oriented internetworking    A set of subnetworks connected physically and thus rendered capable of connection-oriented network service.
connection-oriented service    A type of service offered in some networks. This service has three phases: connection establishment, data transfer, and connection release.
cracker    Someone who attempts to break into computer systems, often with malicious intent.
data circuit-terminating equipment (DCE)    Equipment required to connect a DTE to a line or to a network.
data-link control (DLC)    A set of rules used by nodes at layer 2 within a network. The data link is governed by data-link protocols such as ETHERNET or token ring for example.
data-link control (DLC) protocol    Rules used by two nodes at a data-link layer to accomplish an orderly exchange of information. Examples are ETHERNET, channel, FDDI, and token ring.
data-link layer    Layer 2 of the OSI reference model. It synchronizes transmission and handles error correction for a data link.
data-link level    The conceptual level of control logic between high-level logic and a data-link protocol that maintains control of the data link.
data terminal equipment (DTE)    A source or destination for data. Often used to denote terminals or computers attached to a wide area network.
DECnet    Digital Equipment Corporation’s proprietary network protocol. Versions are identified by their phase number—such as Phase IV and Phase V.
directed broadcast address    In TCP/IP-based environments, an IP address that specifies all hosts on a specific network. A single copy of a directed broadcast is routed to the specified network where it is broadcast to all machines on that network.
DIX Ethernet    Version of Ethernet developed by Digital, Intel, and Xerox.
domain name server    In TCP/IP environments, it is a protocol for matching object names and network addresses. It was designed to replace the need to update /etc/hosts files of participating entities throughout a network.
domain name system (DNS)    The online distributed database system used to map human-readable machine names into IP addresses. DNS servers throughout the connected Internet implement a hierarchical name space that allows sites freedom in assigning machine names and addresses. DNS also supports separate mappings between mail destinations and IP addresses.
dotted-decimal notation    A phrase typically found in TCP/IP network conversations. Specifically, this refers to the addressing scheme of the Internet protocol (IP). It is the representation of a 32-bit address consisting of four 8-bit numbers written in base 10 with periods separating them.
encapsulate    Generally agreed on in the internetworking community to mean surrounding one protocol with another protocol for the purpose of passing the foreign protocol through the native environment.
ETHERNET    A data-link-level protocol. It (Version 2.0) was defined by Digital Equipment Corporation, Intel Corporation, and the Xerox Corporation in 1982. It specified a data rate of 10 Mbits/s, a maximum station distance of 2.8 km, a maximum number of stations of 1024, a shielded coaxial cable using baseband signaling, functionality of CSMA/CD, and a best-effort delivery system.
exterior gateway protocol (EGP)    Routers in neighboring Autonomous Systems use this protocol to identify the set of networks that can be reached within or via each Autonomous System. EGP is being supplanted by BGP.
filter    A device or program that separates data, signals, or material in accordance with specified criteria.
firewall    A system that controls what traffic may enter and leave a site.
frame    One definition generally agreed on as being a packet as it is transmitted across a serial line. The term originated from character-oriented protocols. According to the meaning in OSI environments, it is a data structure pertaining to a particular area of data. It also consists of slots that can accept values of specific attributes.
hierarchical routing    From a TCP/IP perspective, this type of routing is based on a hierarchical addressing scheme. Most TCP/IP routing is based on a two-level hierarchy in which an IP address is divided into a network portion until the datagram reaches a gateway that can deliver it directly. The concept of subnets introduces additional levels of hierarchical routing.
hop count    (1) A measure of distance between two points in the Internet. Each hop count corresponds to one router separating a source from a destination (for example, a hop count of 3 indicates that three routers separate a source from a destination). (2) A term generally used in TCP/IP networks. The basic definition is a measure of distance between two points in an internet. A hop count of n means that n routers separate the source and the destination.
ICMP    Internet Control Message Protocol. Specific to the TCP/IP protocol suite. It is an integral part of the Internet protocol. It handles error and control messages. Routers and hosts use ICMP to send reports of problems about datagrams back to the original source that sent the datagram. ICMP also includes an echo request/reply used to test whether a destination is reachable and responding.
interior gateway protocol (IGP)    Any routing protocol used within an internetwork.
International Organization for Standardization (ISO)    An organization of national standards-making bodies from various countries established to promote development of standards to facilitate international exchange of goods and services, and develop cooperation in intellectual, scientific, technological, and economic activity.
Internet    According to different documents describing the Internet, it is a collection of networks, routers, gateways, and other networking devices that use the TCP/IP protocol suite and function as a single, cooperative virtual network. The Internet provides universal connectivity and three levels of network services: unreliable, connectionless packet delivery; reliable, full-duplex stream delivery; and application-level services such as electronic mail that build on the first two. The Internet reaches many universities, government research labs, and military installations and over a dozen countries.
Internet address    According to TCP/IP documentation, it refers to the 32-bit address assigned to the host. It is a software address that on local (“little i”) internets is locally managed, but on the central (“big I”) Internet is dictated to the user (entity desiring access to the Internet).
Internet Assigned Numbers Authority (IANA)    The authority responsible for controlling the assignment of a variety of parameters, such as well-known ports, multicast addresses, terminal identifiers, and system identifiers.
Internet control message protocol (ICMP)    A protocol that is required for implementation with IP. ICMP specifies error messages to be sent when datagrams are discarded or systems experience congestion. ICMP also provides several useful query services.
Internet gateway routing protocol (IGRP)    A proprietary protocol designed for Cisco routers.
Internet group management protocol (IGMP)    A protocol that is part of the multicast specification. IGMP is used to carry group membership information.
Internet packet exchange (IPX)    A Novell protocol that operates at OSI layer 3. It is used in the NetWare protocols; it is similar to IP in TCP/IP.
Internet protocol (IP)    A protocol used to route data from its source to its destination. A part of TCP/IP protocol.
IP    Internet protocol. The TCP/IP standard protocol that defines the IP datagram as the unit of information passed across an internet and provides the basis for connectionless, best-effort packet delivery service. IP includes the ICMP control and error message protocol as an integral part. The entire protocol suite is often referred to as TCP/IP because TCP and IP are the two fundamental protocols.
IP address    The 32-bit dotted-decimal address assigned to hosts that want to participate in a local TCP/IP internet or the central (connected) Internet. IP addresses are software addresses. Actually, an IP address consists of a network portion and a host portion. The partition makes routing efficient.
IP datagram    A term used with TCP/IP networks. It is a basic unit of information passed across a TCP/IP internet. An IP datagram is to an internet as a hardware packet is to a physical network. It contains a source address and a destination address along with data.
link    A medium over which nodes can communicate using a link layer protocol.
link state protocol    A routing protocol that generates routes using detailed knowledge of the topology of a network.
LLC    Logical link control. According to OSI documentation, a sublayer in the data-link layer of the OSI model. The LLC provides the basis for an unacknowledged connectionless service or connection-oriented service on the local area network.
loopback address    Address 127.0.0.1, used for communications between clients and servers that reside on the same host.
MAC address    A physical address assigned to a LAN interface.
MAC protocol    A Media Access Control protocol defines the rules that govern a system’s ability to transmit and receive data on a medium.
MTU    Maximum transfer unit. The largest amount of data that can be transferred across a given physical network. For local area networks implementing ETHERNET, the MTU is determined by the network hardware. For long-haul networks that use aerial lines to interconnect packet switches, the MTU is determined by software.
multicast    A technique that allows copies of a single packet to be passed to a selected subset of all possible destinations. Some hardware supports multicast by allowing a network interface to belong to one or more multicast groups. Broadcast is a special form of multicast in which the subset of machines to receive a copy of a packet consists of the entire set. IP supports an internet multicast facility.
multicast address    According to Apple documentation, an ETHERNET address for which the node accepts packets just as it does for its permanently assigned ETHERNET hardware address. The low-order bit of the high-order byte is set to 1. Each node can have any number of multicast addresses, and any number of nodes can have the same multicast address. The purpose of a multicast address is to allow a group of ETHERNET nodes to receive the same transmission simultaneously, in a fashion similar to the AppleTalk broadcast service.
multicasting    A directory service agent uses this mode to chain a request to many other directory service agents.
multicast IP address    A destination IP address that can be adopted by multiple hosts. Datagrams sent to a multicast IP address will be delivered to all hosts in the group.
NetBEUI    Local area network protocol used for Microsoft LANs.
NETBIOS    A network programming interface and protocol developed for IBM-compatible personal computers.
network    A collection of computers and related devices connected together in such a way that collectively they can be more productive than standalone equipment.
network address    In general, each participating entity on a network has an address so that it can be identified when exchanging data. According to IBM documentation, in a subarea network, an address consists of subarea and element fields that identify a link, link station, PU, LU, or SSCP.
network layer    According to ISO documentation, it is defined as OSI layer 3. It is responsible for data transfer across the network. It functions independently of the network media and the topology.
octet    Eight bits (a byte).
open shortest path first (OSPF)    A routing protocol based on the least cost for routing.
packet    A term used generically in many instances. It is a small unit of control information and data that is processed by the network protocol.
physical address    An address assigned to a network interface.
physical layer    A term used in OSI circles. It refers to the lowest layer defined by the OSI model. However, layer 0 would be the lowest layer in such a model. This layer (layer 0) represents the medium, whether hard or soft.
point-to-point protocol (PPP)    A protocol for data transfer across serial links. PPP supports authentication, link configuration, and link monitoring capabilities and allows traffic for several protocols to be multiplexed across the link.
presentation layer    According to the OSI model for networks, this is layer 6. Data representation occurs here. Syntax of data such as ASCII or EBCDIC is determined at this layer.
protocol    An agreed-upon way of doing something.
proxy ARP    In TCP/IP networks, this is a technique where one machine answers ARP requests intended for another by supplying its own physical address.
RARP    Reverse address resolution protocol. A TCP/IP protocol for mapping ETHERNET addresses to IP addresses. It is used by diskless workstations who do not know their IP addresses. In essence, it asks “Who am I?” Normally, a response occurs and is cached in the host.
reverse address resolution protocol (RARP)    A protocol that enables a computer to discover its IP address by broadcasting a request on a network.
RFC    Request for comments. Proposed and accepted TCP/IP standards.
routing    The moving of data through paths in a network.
routing information protocol (RIP)    A simple protocol used to exchange information between routers. The original version was part of the XNS protocol suite.
routing policy    Rules for which traffic will be routed and how it should be routed.
routing table    A table containing information used to forward datagrams toward their destinations.
segment  A Protocol Data Unit consisting of a TCP header and optionally, some data. Sometimes used to refer to the data portion of a TCP Protocol Data Unit.
session layer    According to the OSI reference model, this is layer 5. It coordinates the dialog between two communicating application processes.
shortest path first    A routing algorithm that uses knowledge of a network’s topology in making routing decisions.
sliding window    A scenario in which a protocol permits the transmitting station to send a stream of bytes before an acknowledgment arrives.
stub network    A network that does not carry transit traffic between other networks.
subnet address    A selected number of bits from the local part of an IP address, used to identify a set of systems connected to a common link.
subnet mask    A configuration parameter that indicates how many bits of an address are used for the host part. It is expressed as a 32-bit quantity, with 1s placed in positions covering the network and subnet part of an IP address and 0s in the host part.
switch    A layer 2 device that enables many pairs of LAN devices to communicate concurrently.
T1    A digital telephony service that operates at 1.544 megabits per second. DS1 framing is used.
T3    A digital telephony service that operates at 44.746 megabits per second. DS3 framing is used.
TCP    Transmission control protocol. The TCP/IP standard transport-level protocol that provides the reliable, full-duplex, stream service on which many application protocols depend. It is connection-oriented in that before transmitting data, participants must establish a connection.
TELNET    The TCP/IP TCP standard protocol for remote terminal service.
10Base T    An ETHERNET implementation using 10 Mbits/s with baseband signaling over twisted-pair cabling.
TFTP    Trivial file transfer protocol. A TCP/IP UDP standard protocol for file transfer that uses UDP as a transport mechanism. TFTP depends only on UDP, so it can be used on machines such as diskless workstations.
token    The symbol of authority passed successively from one data station to another to indicate which station is temporarily in control of the transmission medium.
token ring    A network with a ring topology that passes tokens from one attaching device to another.
token-ring network    A ring network that allows unidirectional data transmission between data stations by a token-passing procedure.
transport layer    According to the OSI model, it is the layer that provides an end-to-end service to its users.
TTL    Time to live. A technique used in best-effort delivery systems to avoid endlessly looping packets. For example, each packet has a “time” associated with its lifetime.
well-known-port    A term used with TCP/IP networks. In TCP/IP, applications and programs that reside on top of TCP and UDP, respectively, have a designated port assigned to them. This agreed-on port is known as a well-known-port.

 


 
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