CCNA2 M7 Distance Vector Routing Protocol

8/14/2019 CCNA2 M7 Distance Vector Routing Protocol

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CCNA Semester2

Module 7Routing and Routing Protocols

Objectives

Distance vector routing

RIP IGRP


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Distance vector routing loop issues

Routing decisions based on incorrect information results in packets takingpaths that return them to already visited routers

Before network 1 goes down B & D goes via A to this network, C may go via Bto this network

When net 1 is down, A informs B & D about it, C does not yet know

C sends update to D informing that it canget to net 1 via B

D updates this incorrect route overwritingthe previously correct update from A

D sends update to A followed by A sendsupdate to B causing both A & B to alsoupdate the incorrect route

Consequence: Packet originating from Cdestined to net 1 will loop:

C B A D C

Problem: Count to infinity Large number of routing loops results in forever-increasing value of routing

metric, e.g. hop count, or count to infinity


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Route poisoning

To overcome large routing loops Set the hop count to one more than the maximum.

Avoiding routing loops with triggered updates

Triggered update is sent immediately in response tosome change in the routing table.

Triggered updates, used in conjunction with routepoisoning, ensure that all routers know of failed routesbefore any holddown timers can expire.


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Loop prevention: Hold-down timer

If at any time during hold-down timer an update is received from The same neighbor indicating that the network isagain accessible, the router marks

the network as accessible and removes the hold-down timer. A different neighboring router with abetter metricthan originally recorded for the

network, the router marks the network as accessible and removes the hold-downtimer.

A different neighboring router with apoorer metric, the update is ignored.

Routing Information Protocol- RIP -


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Classful Routing vs. Classless Routing

Classful routing must be used with classfulnetwork or subnets with the same subnetmask.

It does not include subnetmask in its routingtable (FLSM) Classless routing allows updating routes with

different subnetmasks therefore it includesubnetmask in routing update (VLSM)

RIP

Distance vector protocol Hop count is used as the metric for path

selection Maximum hop count is 15 Routing update interval is 30s


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RIPv1 and RIPv2

RIP Version 1 is a Classful Routing Protocol, RIP Version 2is a Classless Routing Protocol. RIP v2 enhancementsinclude: Ability to carry additional packet routing information. Authentication mechanism to secure table updates.

Supports variable length subnet masking (VLSM).

Configuring RIP


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Configure RIPv1 and RIPv2

Show ip protocols


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SHOW IP ROUTE command

Show ip route

R 183.8.0.128 [120/1] via 183.8.128.130 , 00:00:17 , Serial0

via 183.8.64.130 , 00:00:17 , Serial1

183.8.0.128 : destination network number

[120/1] : [administrative distance/hop count]

183.8.128.130 : next hop IP address

00:00:17 : latest update was 17 seconds ago

Serial0 : outgoing interface is Serial0

Second line : load sharing


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Troubleshooting RIP update issues

Other commands to troubleshoot RIP: show ip rip database

show ip protocols show ip route debug ip rip {events} show ip interface brief

Load Balancing with RIP


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Interior Gateway Routing Protocol- IGRP -

IGRP

IGRP is a distance vector routing protocoldeveloped by Cisco .

IGRP sends routing updates at 90 secondintervals, advertising networks for a particular autonomous system .


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IGRP features

Key design characteristics of IGRP are a follows: The versatility to automatically handle indefinite, complex topologies The flexibility needed to segment with different bandwidth and delay

characteristics Scalability for functioning in very large networks

IGRP Metrics

The metrics that IGRP uses are: Bandwidth The lowest bandwidth value in the path Delay The cumulative interface delay along the path Reliability The reliability on the link towards the destination as determined

by the exchange of keepalives Load The load on a link towards the destination based on bits per second MTU The Maximum Transmission Unit value of the path.

Default metric use only bandwidth and delay Hop-count is used as a secondary metric to prevent loop


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SHOW IP PROTOCOLS command

IGRP routes

IGRP advertises three types of routes: Interior System Exterior


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IGRP Routes

AS = 100 AS = 200

Configuring IGRP


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Verifying IGRP configuration

Additional commands for checking IGRPconfiguration are as follows:

show interface interface [brief] show running-config show ip protocols

Troubleshooting IGRP

The following commands are useful whentroubleshooting IGRP: show ip protocols show ip route debug ip igrp events

debug ip igrp transactions ping traceroute


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Default static ip route

Create a default route on the router which isbeing configured:

ip route 0.0.0.0 0.0.0.0 { ip_next_hop | interface } Static routes can be advertised to other router

via dynamic routing update using:redistribute static

IGRP has no concept of route 0.0.0.0/0

Default Network

Tell other router to choose the network as thedefault route:

ip default-network { network_number }

Network_number must be a known classfullnetwork (taken from routing table)

IGRP may use this with default static ip route For a network, default route configuration is

only configured on gateway router


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Default Route

Summary

How routing loops occur in distance vector Preventing routing loop solution Configuring RIP IGRP features

IGRP metrics IGRP routes Configuring IGRP


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Lab Topology 1 - RIP

Lab_A

Lab_B

Lab_C

S0/0

S0/1

S0/0

F0/0

S0/1

F0/0

Lab_D

Lab_E

Lab_F

S0/0

S0/1

S0/0

F0/0

S0/1

F0/0

F0/0 F0/0

S0/1S0/0

Site1 Site2

Port Lab_A Lab_B Lab_C Lab_D Lab_E Lab_F

S0/0 201.10.11.1/24 199.6.13.1/24 204.204.7.1/24 192.168.3.1/24

204.204.7.2/24

172.18.11.1/16

34.10.120.1/16 N/A

S0/1 N/A 201.10.11.2/24 199.6.13.2/24 192.168.3.2/24 34.10.210.5/16

F0/0 172.17.11.1/16 172.16.11.1/16 172.17.11.2/16 172.16.11.2/16 172.18.11.2/16

Lab Topology 2 2 IGRP AS with default routes

Internet

Lab_A

Lab_B

Lab_C Lab_D

Lab_E

Lab_F

IGRP 100172.20.0.0/16

IGRP 200192.168.1.0/24

172.16.2.1/16 172.16.2.2/16


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CCNA2 Module7

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CCNA2 M7 Distance Vector Routing Protocol