Cisco Networking Academy Program CCNA 1 and 2 Companion Guide, Revised part 51 is the Cisco approved textbook to use alongside version of the Cisco Networking Academy Program CCNA 1 and CCNA 2 web-based courses. The topics covered provide you with the necessary knowledge to begin your preparation for the CCNA certification exam (640-801, or 640-821 and 640-811) and to enter the field of network administration. | I Page 469 Tuesday May 20 2003 2 53 PM Key Terms 469 protocol stack A set of related communications protocols that operate together and as a group address communication at some or all of the seven layers of the OSI reference model. Not every protocol stack covers each layer of the model and often a single protocol in the stack addresses a number of layers at once. TCP IP is a typical protocol stack. routed protocol Any network protocol that provides enough information in its network layer address to allow a packet to be forwarded from one host to another host based on the addressing scheme. router A network-layer device that uses one or more metrics to determine the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network-layer information contained in routing updates. Occasionally called a gateway although this definition of gateway is becoming increasingly outdated . Routing Information Protocol RIP An IGP supplied with UNIX BSD systems. The most common IGP in the Internet. RIP uses hop count as a routing metric. routing metric A method by which a routing algorithm determines that one route is better than another. This information is stored in routing tables and is sent in routing updates. Metrics include bandwidth communication cost delay hop count load MTU path cost and reliability. Sometimes simply called a metric. routing protocol A protocol that accomplishes routing through the implementation of a specific routing algorithm. Examples of routing protocols are IGRP OSPF and RIP. routing table A table stored in a router or some other internetworking device that keeps track of routes to particular network destinations and in some cases metrics associated with those routes. subnet address A portion of an IP address that is specified as the subnetwork by the subnet mask. subnet mask A 32-bit address mask used in IP to indicate the bits of an IP address that are used for the subnet
