Cisco Systems CCNA 2 manual Path determination, Routing configuration, Routing protocols

Certification-Level Claim: Students can evaluate the characteristics of routing protocols.

Hands-on skills: none

6.3.1 Path determination

Path determination occurs at the network layer, or Layer 3, for traffic that goes through a network cloud. The path determination function enables a router to evaluate the available paths to a destination and to establish the preferred way to handle a packet. This information can be configured by a network administrator or collected through the dynamic processes that operate in the network. Routing protocols help prevent routing loops and use fewer resources. An administrator can configure static routes for all reachable networks. Routers perform two primary functions:

•Path selection

•Switching

During path selection, the routing table is examined to determine the next hop destination of a packet and which interface to use to reach that next hop destination. Switching occurs when a packet is moved to the interface and a frame is created to send the information.

6.3.2 Routing configuration

Global and interface parameters must be set when an IP routing protocol is selected. Global tasks include the selection of a routing protocol, either RIP or IGRP, and IP network numbers must be indicated. It is important to check the interface IP address and subnet configuration. A common problem is to assign the wrong IP address or subnet mask. The network command is required because it enables the routing process to determine which interfaces will send and receive routing updates. A network statement must be entered for all connected networks. Two common problems are failure to enable the routing protocol or failure to enter all the connected networks.

6.3.3 Routing protocols

Examples of IP routing protocols include the following:

•RIP – a distance-vector interior routing protocol

•IGRP – a Cisco distance-vector interior routing protocol

•OSPF – a link-state interior routing protocol

•EIGRP – a balanced hybrid distance-vector interior routing protocol

•BGP – an exterior routing protocol

Make sure students understand that each routing protocol has advantages and disadvantages. The protocols have different characteristics and were designed for different purposes. In some instances administrators will want to use RIP and other times they will use BGP.

72 - 238 CCNA 2: Routers and Routing Basics v3.1 Instructor Guide – Module 6 Copyright ♥ 2004, Cisco Systems, Inc.