CCNA 6.4 Dynamic Routing

• Dynamic routing is when protocols are used to find networks and update routing tables on routers
• Two types of routing protocols are used in internetwork: interior gateway protocols (IGPs) and exterior gateway protocols (EGPs)
• IGPs are used to exchange routing info with routers in the same autonomous system (AS)
• An AS is a collection of networks under the same administrative domain (all routers sharing the same routing table info)
• EGPs are used to communicate between ASes. ( ie. Border Gateway Protocol - BGP)
• Administrative distance (AD) is used to rate the trustworthiness of routing info received on a router from a neighbour router
• AD is an integer from 0 - 255 with 0 is the most trusted and 255 means no traffic will be passed via this route
• AD, routing protocol metrics ( hop count, bandwidth) are used to determine best path to remote network:

• There are three classes of routing protocols: Distance vector, Link state & Hybrid
• Distance-vector protocols find the best path to a remote network by judging distance - #s of hop. (ex. RIP, IGRP)
• Link-state protocols (Shortest-path-first protocol) create three separate tables: one keeps track of directly attached neighbors, one determines the topology of entire internetwork, one used as routing table. (ex. OSPF)
• Hybrid protocols used both distance-vector and link-state protocols. (ex. EIGRP)