7.0 Enhanced IGRP (EIGRP) & Open Shortest Path First (OSPF)

• EIGRP is proprietary Cisco protocol
• OSPF is another popular routing protocol

6.8 Verifying Your Configurations

Following commands are used to verify routed and routing protocols:

• show ip route
• show ip protocols
• debug ip rip

6.7 Interior Gateway Routing Protocol (IGRP)

• IGRP is a Cisco-proprietary distance-vector routing protocol (all routers in network must be Cisco)
• Main difference btw IGRP & RIP : During IGRP configuration, autonomous system number is used (all router must use same number to share routing info)
• IGRP vs RIP :

6.6 Routing Information Protocol (RIP)

• RIP version 1 uses only classful routing - all devices in the network must use the same subnet mask
• RIP version 2 uses classless/prefix routing - send subnet mask information with route updates
• RIP uses four different kinds of timers - Route update timer (30s), Route invalid timer (180s), Holddown timer (180s), Route flush timer (240s)
• RIP v1 vs. RIP v2:

• RIPv2 is classless and works in VLSM and dis-contiguous networks

CCNA 6.5 Distance-Vector Routing Protocols

• DVR protocol passes complete routing table contents to neighboring routers, which then combined the received routing entries with their own routing tables to complete the router's routing table
• Pinhole congestion (RIP) :

• Initial routing table with DVR (IP, Exit Interface, Hop Count):

• DVR - slow convergence time
• Converged routing tables:

• DVR keeps track of changes to internetwork by broadcasting periodic routing updates out all active interface
• Routing loops (counting to infinity) occur when every router isn't updated simultaneously
• Maximum hop - RIP up to 15 (solve routing loops)
• Splilt horizon enforce the rule that routing info cannot be sent back in the direction from which it was received (solve routing loops)
• Route poisoning assigns down network with hop counts of 16 or unreachable/infinite (solve routing loops)
• A holddown prevents regular update messages from reinstating a route that is going up and down (flapping)

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)

CCNA 6.3 Configuring IP Routing

• When a router receives a packet for a network that isn't listed in the router, it would just discard the packet.
• Static Routing benefits': No overhead on router CPU, No bandwidth usage between routers & security
• Static Routing disadvantages': Not feasible in large network,
• Static Route command syntax:

ip route [destination_network] [mask] [next-hop address / exitinterface] [administrative_distance] [permanent]

• Default routing sends packets with a remote destination network not in the routing table to the next-hop router