| A | B |
|---|
| IP | Network layer protocol in the TCP/IP stack offering a connectionless internetwork service; provides features for addressing, type-of-service specification, fragmentation, reassembly, and security |
| router | Network layer device that uses one or more metrics to determine the optimal path along which network traffic should be forwarded; forwards packets from one network to another based on network layer information; occasionally called a gateway. |
| packet | Logical grouping of information that includes a header containing control information and (usually) user data; most often are used to refer to network layer units of data |
| RAM | Volatile memory that can be read and written to by a microprocessor |
| ROM | Nonvolatile memory that can be read, but not written to, by the microprocessor |
| operating system | Software that performs basic tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices, facilitating networking, and managing file systems |
| local-area networks (LAN) | High-speed, low-error data network convering a relatively small geographic area; connect workstations, peripherals, terminals, and other devices in a single building or other geographically limited area |
| wide-area networks (WAN) | Data communications network that serves users across a broad geographic area and often uses transmission devices provided by common carriers |
| Ethernet | Baseband LAN specification invented by Xerox Corporation and developed jointly by Xerox, Intel, and Digital Equipment Corporation; uses CSMA/CD and runs over a variety of cable types at 10 Mbps; similar to IEEE 802.3 series of standards |
| Internet Service Provider (ISP) | A company that provides access to the Internet to individuals or companies |
| best path | The fastest path, to a certain destination, based on the routing protocol's metric |
| routing table | A table stored in the memory of a router or some other internetworking device that keeps track of routes to particular network destinations; a router uses this list of networks to determine where to send data |
| Point-to-Point Protocol (PPP) | Provides router-to-router and host-to-network connections over synchronous and asynchronous circuits; designed to work with several network layer protocols, such as IP, IPX, and ARA; also has built-in security mechanisms, such as CHAP and PAP; relies on two protocols: LCP and NCP |
| serial | Method of data transmission in which the bits of data characters are transmitted sequentially over a single channel |
| Frame Relay | A packet-switched data link layer protocol that handles multiple virtual circuits used between connected devices |
| Asynchronous Transfer Mode (ATM) | The international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells; fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays; designed to take advantage of high-speed transmission media such as E3, SONET, and T3 |
| dynamic routing protocols | Routing that adjusts automatically to network topology or traffic changes |
| unified communications | A communications system for voice, video, and data; the system integrates wired, wireless, and mobile devices to create a secure solution for enterprise networks |
| media | various physical environments through which transmission signals pass |
| ARP | Internet protocol used to map an (a known) IP address to a (an unknown) MAC address |
| MAC address | Standardized data link layer address that is required for every port or device that connects to a LAN; other devices in the nework use these address to locate specific ports in the network and to create and update routing tables and data structures; 6 bytes long and contolled by the IEEE |
| flash | A variation of electronically erasable programmable read-only memory; is erasable and writable; the storage card where the router stores the IOS image |
| NVRAM | Non-volatile random-access memory; random-access memory that retains its contents when the power is shut off |
| IPv6 | A network layer protocol for packet-switched internetworks; the successor for IPv4 for general use on the Internet |
| IS-IS | Intermediate System-to-Intermediate System protocol; based on a routing method known as DECnet Phase V routing, in which routers known as intermediate systems exchange data about routing using a single metric to determine the network topology; developed by the ISO as part of its OSI model |
| static routing | Routing that depends on manually entered routes in the routing table |
| RIP | Routing Information Protocol; IGP supplied with UNIX BSD systems; the most common IGP in the Internet; uses hop count as its only routing metric |
| EIGRP | Enhanced Interior Gateway Routing Protocol; advanced version of IGRP developed by Cisco; provides superior convergence properties and operating efficiency, and combines the advantages of link-state protocols with those of distance vector protocols |
| OSPF | Open Shortest Path First; link-state, hierarchical IGP routing algorithm proposed as a successor to RIP in the Internet community; features include least-cost routing, multipath routing, and load balancing |
| setup mode | A Cisco router mode which includes a dialogue of questions that the administrator must answer to set up a basic router configuration |
| power-on self test (POST) | Set of hardware diagnostics that runs on a hardware device when that device is powered up |
| console port | DTE port through which commands are entered into a host |
| DSL | Digital subscriber line; network technology that delivers high bandwidth over conventional copper wiring at limited distances |
| ISDN | Integraded Services Digital Network; communication protocol offered by telephone companies that permits telephone networks to carry data, voice, and other source traffic |
| cable | Transmission medium of copper wire or optical fiber wrapped in a protective cover |
| LED | Light emitting diode; semiconductor device that emits light produced by converting electrical energy |
| NIC | Network interface card; computer hardware that is designed to allow computers to communicate over a computer network |
| host | computer system on a network; similar to node, except that this usually implies a computer system, whereas a node generally applies to any networked system, including access servers and routers |
| gateway | A device on a network that serves as an access point to other networks |
| privileged EXEC mode | The administration mode for the router or switch; this mode allows you to view router settings that are considered only accessible to the administrator |
| Telnet | Standard terminal emulation protocol in the TCP/IP protocol stack; 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 |
| next-hop | The next point of routing; when routers are not directly connected to the destination network, they will have a neighboring router that provides the next step in routing the data to its destination |
| neighbor | In OSPF, two routers that have interfaces to a common network |
| metric | Method by which a routing algorithm determines that one route is better than another |
| administrative distance | Rating of the trustworthiness of a routing information source; often expressed as a numerical value between 0 and 255, the higher the value, the lower the trustworthiness rating |
| hub-and-spoke | A WAN topology in which various branch offices are connected through a centralized hub or headquarters |
| IGRP | Interior Gateway Routing Protocol; IGP developed by Cisco to address the issues associated with routing in large, heterogeneous networks |
| BGP | Border Gateway Protocol; interdomain routing protocol; exchanges reachability information with other BGP systems |
| asymmetric routing | When a path from network 1 to network 2 is different from the path from network 2 to network 1 |
| TTL | Time to Live; Field in an IP header that indicates how long a packet is considered valid |
| datagram | Logical grouping of information sent as a network layer unit over a transmission medium without prior establishment of a virtual circuit; the primary information units in the Internet; |
| NAT | Network Address Translation; mechanism for reducing the need for gloabally unique IP addresses; allows an organization with addresses that are not globally unique to connect to the Internet by translating those addresses into globally routable address space |
| equal-cost metric | A metric that has the same value on multiple paths to the same destination |
| equal-cost load balancing | When a router utilizes multiple paths with the same administrative distance and cost to a destination |
| unequal-cost load balancing | Load balancing that uses multiple paths to the same destination that have different costs or metrics |
