Week 3 - Routing Concepts Tuesday, April 14, 2020 3:50 PM 14.1 Path Determination 14.1.1 - Two Functions of Router - Before a router forwards a packet anyway, it has to determine the best path for the packet to take. - Ethernet switches are used to connect end devices and other intermediary devices to the same network. - A router connects multiple networks, which means that it has multiple interfaces that each belong to a different IP network. - When a router receives an IP packet on one interface, it determines which interface to use to forward the packet to the destination. o This is known as routing. The interface that the router uses to forward the packet may be the final destination, or it may be a network connected to another router that is used to reach the destination network. o Each network that a router connects to typically requires a separate interface - not always the case. - The primary functions of a router are to determine the best path to forward packets based on the information in its routing table, and to forward packets toward their destination. 14.1.2 - Router Functions example LAN 192.168.2.0/24 LAN R2 192:168.1:0/24 Rif show ip route Codes: C - connected, 3 - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF N95A external type 2 E1 - OSPF external type 1, E2 - 03PF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - 19-IS level-2 ia - IS-IS inter area, * - candidate default U - per-user static route, o - ODR P - periodic downloaded static route 192.168.3.0/24 Routers use the routing table like a map to discover the best path for a given network. Gateway of last resort is not set C c 192.168.1.0/24 is directly connected, FastEthernet0/0 192.168.2.0/24 is directly connected, Seria10/0/0 192.168.3.0/24 [1/0] via 192.168 2.2 Routing and Switching Essentials Page 1
LAN 192.168.2.0/24 LAN 192.168.1.0/24 R2 follows the same process R1 R2 192.168.3.0/24 R24 show ip route Codea: C - connected, 3 - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF N93A external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - 19-IS, L1 - IS-IS level-1, L2 - IS-IS level-2 ia - IS-IS inter area, " - candidate default U - per user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set C 192.168_3.0/24 is directly connected, FastEthernet0/0 C 192.168.2.0/24 is directly connected, Seria10/0/0 192 168 1.0/24 [1/0] wia 192.168 2 1 14.1.3 - Best Path Equals Longest Match - The best