Sybex CCNA Chapter 6: IP Routing Instructor & Todd Lammle

Chapter 6 Objectives Understanding IP routing Static routing Dynamic routing –RIP –RIPv2 –Verifying routing 2

To route a router need to know: –Remote Networks –Neighbor Routers –All Possible routes to remote network –The absolute best route to all remote networks –Maintain and verify the routing information What is Routing? CB A D

Basic Path Selection What interface will the router send out a packet if it has destination address of ?

Simple IP Routing B A e0 >ping B s0 Host A Host B

Routing/PDU Example: Host A Web browses to the HTTP Server…. 3. The destination port number in a segment header will have a value of __ 1. The destination address of a frame will be the _______________________ 2. The destination IP address of a packet will be the IP address of the________________________________

SO Static Routes B A B Stub Network SO A Routes must be unidirectional

ip route remote network [mask] {address|interface} [distance] [permanent] Router(config)#ip route remote_network mask next_hop Static Route Configuration

ip route or ip route s0 Static Route Example SO B A B Stub Network SO

Default Routes SO B A B Stub Network SO To send packets with a remote destination network not in the routing table to the next-hop router, only used for stub networks. ip route ip classless

Routing protocols are used between routers to: –Determine the path of a packet through a network –Maintain routing tables –Two types: interior/exterior gateway protocols (I/EGPs) –Examples: IGP: RIP, IGRP; EGP: Border Gateway Protocol (BGP) Routing Protocols

Autonomous System 1Autonomous System 2 IGPs: RIP, IGRP EGPs: BGP Routing Protocols An autonomous system is a collection of networks under a common administrative domain, i.e., all routers sharing the same routing table are in the same AS. IGPs operate within an autonomous system. EGPs connect different autonomous systems.

Classful Routing Overview Classful routing protocols do not include the subnet mask with the route advertisement. –Within the same network, consistency of the subnet masks is assumed. –Summary routes are exchanged between foreign networks. –Examples of classful routing protocols: RIP Version 1 (RIPv1) IGRP

Classless Routing Overview Classless routing protocols include the subnet mask with the route advertisement. –Classless routing protocols support variable-length subnet masking (VLSM). –Summary routes can be manually controlled within the network. –Examples of classless routing protocols: RIP Version 2 (RIPv2) EIGRP OSPF IS-IS

IGRP Administrative Distance=100 Router D Router B Router A Router C RIP Administrative Distance=120 Default Administrative Distance Directly Connected: 0 Static Route: 1 RIP: 120 IGRP: 100 EIGRP: 90 OSPF: 110 Administrative Distance

CB A D Routing Table Routing Table Routing Table Routing Table Routing Table Routing Table Routing Table Routing Table Distance—How far Vector—In which direction All routers just broadcast their entire routing table out all active interfaces on periodic time intervals Distance vector algorithms do not allow a router to know the exact topology of an internetwork. Distance Vector

Discovering Routes

Discovering Routes: Converged Routing Tables

Routing Loops

Stop Router Loops Maximum hop count: RIP permits a hop count of up to 15. Split horizon: routing information cannot be sent back in the direction from which it was received. Route poisoning: advertising the downed network as unreachable

64kbps T1 –Hop count metric selects the path, 16 is unreachable –Full route table broadcast every 30 seconds –Load balance maximum of 6 equal cost paths (default = 4) –RIPv2 supports VLSM and Discontiguous networks RIP Overview

Router(config)#router rip Router(config-router)#network network-number* network network router RIP network network router RIP *Network is a classful network address. Every device on network uses the same subnet mask RIP Routing Configuration

RIP Version 2 Allows the use of variable length subnet masks (VLSM) by sending subnet mask information with each route update Distance Vector – same AD, and timers. Easy configuration, just add the command “version 2” under the router rip configuration router rip network version 2

RIPv1 vs. RIPv2 RIPv1RIPv2 Distance vector Maximum hop count 15 ClassfulClassless Broadcast basedMulticast No support for VLSMSupports VLSM No authenticationMD5 authentication No support for discontiguous networks Supports discontiguous networks

Interior Gateway Routing Protocol Maximum hop count: 255 for larger network, default 100 Composite metric: bandwidth and delay of the line. Config t router igrp 10

IGRP vs. RIP Large networkSmall network Uses AS number for activation Uses network address, with all subnet and host bits off Full route table update per 90 sec Full route table update per 30 sec AD 100AD 120 Uses bandwidth and delay of the line as metric, maximum hop count 255 Uses only hop count to determine the best path to a remote network, max 15

Discontiguous Addressing Two networks of the same classful networks are separated by a different network address / / /24 –RIPv1 and IGRP do not advertise subnet masks, and therefore cannot support discontiguous subnets. –OSPF, EIGRP, and RIPv2 can advertise subnet masks, and therefore can support discontiguous subnets.

Passive Interface Maybe you don’t want to send RIP updates out your router interface connected to the Internet. Use the passive-interface command: Router(config)#router rip Router(config-router)#passive-interface serial0 This allows a router to receive route updates on an interface, but not send updates via that interface S0 Gateway Internet Updates X X

Verifying RIP Router#show ip protocols Router#show ip route Router#debug ip rip Router#undebug all (un all)

Summary –Open your books and go through all the written labs and the review questions. –Review the answers in class. 30