ccna: cisco certified network associate study guide

© Wiley Inc. 2006. All Rights Reserved.

CCNA: Cisco Certified Network Associate Study

Guide

CHAPTER 6: Enhanced IGRP (EIGRP) and

Open Shortest Path First (OSPF)


The CCNA exam topics covered in this chapter include the following:

Planning & Designing• Select an appropriate routing protocol based on user requirements• Design a simple internetwork using Cisco technology

Implementation & Operation

• Configure routing protocols given user requirements


What Is Enhanced IGRP (EIGRP)?

• Enhanced IGRP supports:– Rapid convergence– Reduced bandwidth usage– Multiple network-layer support– Uses Diffused Update Algorithm (DUAL) to select loop-free

routes and enable fast convergence– Up to six unequal paths to a remote network (4 by default)

EnhancedIGRP

IPX RoutingProtocols

AppleTalk Routing Protocol

IP RoutingProtocols

IPX RoutingProtocols

AppleTalk Routing Protocol

IP RoutingProtocols


Comparing EIGRP and IGRP

– Similar metric– Same load balancing– Improved convergence time– Reduced network overhead– Maximum hop count of 255

(100 default)– EIGRP can differentiate

between internal and external routes


EIGRP for IP• No updates. Route updates sent only when

a change occurs – multicast on 224.0.0.10• Hello messages sent to neighbors every 5

seconds (60 seconds in most WANs)

Enhanced IGRP

EIGRP EIGRP

hello


EIGRP TerminologyNeighbor Table—IPNext Hop Interface Router

Topology Table—IPDestination 1 SuccessorDestination 1 Feasible Successor

Routing Table—IPDestination 1 Successor

Note: A feasible successor is a backup route and stored in the Topology table


EIGRP Tables• The neighbor table and

topology table are held in ram and are maintained through the use of hello and update packets.

Enhanced IGRP

EIGRP EIGRP

hello

To see all feasible successor routes known to a router, use the show ip eigrp topology command


Successor routes• Successor route is used by EIGRP to

forward traffic to a destination• A successor routes may be backed up

by a feasible successor route• Successor routes are stored in both the

topology table and the routing table

Routing Table—IPDestination 1 Successor

Topology Table—IPDestination 1 SuccessorDestination 1 Feasible Successor


Choosing Routes

• EIGRP uses a composite metric to pick the best path: bandwidth and delay of the line

• EIGRP (and IGRP) can load balance across six unequal cost paths to a remote network (4 by default)

IPX

19.2

T1

T1 T1

IPX

AppleTalk

IP

AppleTalk

IPA B

DC


Configuring EIGRP for IP

172.16.10.010.110.1.0192.168.0.0

TokenRing

AS=10

Router(config)#router eigrp 10Router(config-router)#network 10.0.0.0Router(config-router)#network 172.16.0.0

192.168.0.0

A C

B

Enable EIGRP

Assign networks

If you use the same AS number for EIGRP as IGRP, EIGRP will automatically redistribute IGRP into EIGRP


RedistributionRedistribution is translating one

type of routing protocol into another.

Router D

Router B

Router A

Router C

EIGRP IGRP

IGRP and EIGRP translate automatically, as long as they are both using the same AS number


Route PathAssuming all default parameters, which

route will RIP (v1 and v2) take, and which route will EIGRP take?

T1 T1

100BaseT

100BaseT

10BaseT

56K


Verifying Enhanced IGRP Operation

show ip protocolsRouter#

show ip route eigrp Router#

show ip eigrp traffic Router#

show ip eigrp neighbors Router#

show ip eigrp topology Router#

• Displays the neighbors discovered by IP Enhanced IGRP

• Displays the IP Enhanced IGRP topology table

• Displays current Enhanced IGRP entries in the routing table

• Displays the parameters and current state of the active routing protocol process

• Displays the number of IP Enhanced IGRP packets sent and received


Show IP Route

-D is for “Dual”-[90/2172] is the administrative distance and cost of the route. The cost of the route is a composite metric comprised from the bandwidth and delay of the line

P1R1#sh ip route[output cut]Gateway of last resort is not setD 192.168.30.0/24 [90/2172] via 192.168.20.2,00:04:36, Serial0/0C 192.168.10.0/24 is directly connected, FastEthernet0/0D 192.168.40.0/24 [90/2681] via 192.168.20.2,00:04:36, Serial0/0C 192.168.20.0/24 is directly connected, Serial0/0D 192.168.50.0/24 [90/2707] via 192.168.20.2,00:04:35, Serial0/0P1R1#


•Open standard•Shortest path first (SPF) algorithm•Link-state routing protocol (vs. distance vector)•Can be used to route between AS’s

Introducing OSPF


OSPF Hierarchical Routing

• Consists of areas and autonomous systems• Minimizes routing update traffic• Supports VLSM• Unlimited hop count


Link State Vs. Distance Vector

Link State:• Provides common view of entire topology• Calculates shortest path• Utilizes event-triggered updates• Can be used to route between AS’s

Distance Vector:•Exchanges routing tables with neighbors•Utilizes frequent periodic updates


Types of OSPF Routers

InternalRouters

Area 1 Area 2

ASBR andBackbone

Router

Backbone/InternalRouters

ABR and Backbone

Router

Backbone Area 0

ABR and Backbone

Router

InternalRouters

•External AS


Router(config-router)#network address mask area area-id

Assigns networks to a specific OSPF area

Router(config)#router ospf process-id

Defines OSPF as the IP routing protocolNote: The process ID is locally significant and is needed

to identify a unique instance of an OSPF database

Configuring Single Area OSPF


OSPF Example

hostname R3

router ospf 10 network 10.1.2.3 0.0.0.0 area 0network 10.1.3.1 0.0.0.0 area 0

hostname R2

router ospf 20network 10.0.0.0 0.255.255.255 area 0

hostname R1

router ospf 30network 10.1.0.0 0.0.255.255 area 0network 10.5.5.1 0.0.0.0 area 0

R3

R2R1

10.1.2.0

10.1.1.0

10.5.5.0

Area 010.1.3.0


Router#show ip ospf interface

Verifying the OSPF Configuration

Displays area-ID and adjacency information

Router#show ip protocols

Verifies that OSPF is configured

Router#show ip route

Displays all the routes learned by the router

Router#show ip ospf neighbor

Displays OSPF-neighbor information on a per-interface basis


OSFP Neighbors• OSPF uses hello packets to create

adjacencies and maintain connectivity with neighbor routers

• OSPF uses the multicast address 224.0.0.5

Hello?224.0.0.5

•Hello packets provides dynamic neighbor discovery•Hello Packets maintains neighbor relationships•Hello packets and LSA’s from other routers help build and maintain the topological database


OSPF Terminology

• Neighbor

• AdjacencyNeighbors

Cost=6

ABR

BDR

DR

Non-DRAdjacencies


Router ID (RID)

Each router in OSPF needs to be uniquely identified to properly arrange them in the Neighbor tables.


Electing the DR and BDR

• OSPF sends Hellos which elect DRs and BDRs

• Router form adjacencies with DRs and BDRs in a multi-access environment

Multicast Hellos are sent and compared

Router with Highest Priority is Elected as DR

Router with 2nd Highest Priority is Elected as BDR


Configuring Loopback Interfaces

Router ID (RID): – Number by which the router is known to OSPF– Default: The highest IP address on an active interface at the

moment of OSPF process startup– Can be overridden by a loopback interface: Highest IP address

of any active loopback interface – also called a logical interface


Interface PrioritiesWhat is the default OSPF interface priority?

Router# show ip ospf interface ethernet0/0Ethernet0 is up, line protocol is upInternet Address 192.168.1.137/29, Area 4Process ID 19, Router ID 192.168.1.137, Network Type BROADCAST,Cost: 10 Transmit Delay is 1 sec, State DR, Priority 1Designated Router (ID) 192.168.1.137, Interface address 192.168.1.137No backup designated router on this networkTimer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5Hello due in 00:00:06Index 2/2, flood queue length 0Next 0x0(0)/0x0(0)Last flood scan length is 0, maximum is 0Last flood scan time is 0 msec, maximum is 0 msecNeighbor Count is 0, Adjacent neighbor count is 0Suppress hello for 0 neighbor(s)


Ensuring your DR

What options can you configure that will ensure that R2 will be the DR of the LAN segment?


Configuring Wildcards

If you want to advertise a partial octet (subnet), you need to use wildcards.– 0.0.0.0 means all octets match exactly– 0.0.0.255 means that the first three match

exactly, but the last octet can be any value

After that, you must remember your block sizes….


Wildcard

The wildcard address is always one less than the block size….– 192.168.10.8/30 = 0.0.0.3– 192.168.10.48/28 = 0.0.0.15– 192.168.10.96/27 = 0.0.0.31– 192.168.10.128/26 = 0.0.0.63


Wildcard Configuration of the Lab_B Router

• Lab_A• E0:

192.168.30.1/24• S0: 172.16.10.5/30

• Lab_B• E0: 192.168.40.1/24• S0: 192.168.10.10/30• S1: 192.168.10.6/30

• Lab_C• E0:

192.168.50.1/24• S1:

172.16.10.9/30

ccna: cisco certified network associate study guide

Documents