Route Redistribution © 2005 Cisco Systems, Inc. All rights ... · PDF fileRoute...


Basic Route Redistribution

Presented by:Allan JohnsonCisco Academy Conference 2005


Outline of Discussion

• Route Redistribution Overview

• Example 1: IGRP and EIGRP Automatic Redistribution

• Example 2: RIP and OSPF Redistribution

• Example 3: EIGRP and OSPF Redistribution


Route Redistribution Overview


Advanced Topic for CCNA Students

• Route Redistribution is a CCNP-level objective:Exam 642-801 BSCI

Identify the steps to configure route redistribution in a network.

• However, a basic understanding of route redistribution will help your students integrate knowledge of routing protocol features and configurations.


Route Redistribution Defined

• Routers are capable of using multiple routing protocols simultaneously.

The Cisco IOS can redistribute or inject routes from one routing protocol or process into another.

For example: RIP routes can be injected into an OSPF process with a RIP hop count metric converted to an OSPF cost metric.

The RIP route then becomes an OSPF route to all other OSPF routers in routing domain.


Why use Route Redistribution?

• Route Redistribution increases administrative overhead and complexity.

Then why use it?

Mixed-vendor environments

Support for legacy systems that only understand RIP

Temporary solution during a migration

As a simple solution for policy routing


Disadvantages to Route Redistribution

• Routing LoopsTwo-Way Redistribution between two domains with two ASBRs can cause loops

• Incompatible routing informationMay result in suboptimal route selection because metrics differ between routing protocols

• Inconsistent convergence timeRIP coverges slower than EIGRP


Guidelines to Follow for Route Redistribution

• Be very familiar with your network.

• Do not overlap routing protocols.

• Use one-way redistribution with multiple boundary routers.

• Use two-way redistribution with a single boundary router.


Example 1:IGRP and EIGRP Automatic Redistribution


IGRP and EIGRP are compatible

• IGRP and EIGRP automatically redistribute routes as long as the Autonomous System Boundary Router (ASBR) uses the same AS number for both routing processes.

• An ASBR routes between two or more routing processes.


Basic Routing Configurations

ANAHEIM#show run!router eigrp 100network 192.168.1.0network 192.168.224.0

FT_WORTH#show run!router eigrp 100network 192.168.2.0network 192.168.224.0!router igrp 100network 192.168.240.0

RICHMOND#show run!router igrp 100network 192.168.3.0network 192.168.240.0


Verification of Automatic Redistribution

RICHMOND#show ip route

Codes: C - connected, S - 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 NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-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

I 192.168.224.0/24 is possibly down, routing via 192.168.240.1, Serial1/0

192.168.240.0/30 is subnetted, 1 subnets

C 192.168.240.0 is directly connected, Serial1/0

I 192.168.1.0/24 [100/10486] via 192.168.240.1, 00:00:46, Serial1/0

I 192.168.2.0/24 [100/8486] via 192.168.240.1, 00:00:46, Serial1/0

C 192.168.3.0/24 is directly connected, FastEthernet0/0



FT_WORTH#show ip route









192.168.224.0/24 is variably subnetted, 2 subnets, 2 masks

D 192.168.224.0/24 is a summary, 00:02:47, Null0

C 192.168.224.0/30 is directly connected, Serial0/0



D 192.168.1.0/24 [90/2172416] via 192.168.224.1, 00:02:15, Serial0/0


I 192.168.3.0/24 [100/8486] via 192.168.240.2, 00:00:14, Serial1/0



ANAHEIM#show ip route









192.168.224.0/24 is variably subnetted, 2 subnets, 2 masks

D 192.168.224.0/24 is a summary, 00:03:03, Null0

C 192.168.224.0/30 is directly connected, Serial0/0


D EX 192.168.240.0 [170/2681856] via 192.168.224.2, 00:03:05, Serial0/0


D 192.168.2.0/24 [90/2172416] via 192.168.224.2, 00:03:05, Serial0/0

D EX 192.168.3.0/24 [170/2684416] via 192.168.224.2, 00:03:05, Serial0/0


eLab: IGRP and EIGRP Auto Redistribution

• The links below will take you to a menu for all the eLabs used in this presentation.

Try the Local Link first

Use the Remote Link for web access

• Once you access the menu of activities, choose the “IGRP and EIGRP Automatic Redistribution”activity.

You may need to “Refresh” the page to reload the eLabmenu if all three eLabs do not appear.


Example 2:Redistributing RIP and OSPF


Overview of RIP and OSPF Redistribution

• Both RIP and OSPF are open standard routing protocols.

• Most OSPF networks also use RIP somewhere within the internetwork to communicate with hosts or subnets that do not use OSPF.

• In our scenario, the Anaheim router can only route using RIP

FtWorth must be configured to redistribute the RIP routes to Richmond.


Basic routing configurations

• Notice that FtWorth is configured with both OSPF and RIP.

RICHMOND#show run!router ospf 1network 192.168.3.0 0.0.0.255 area 0network 192.168.240.0 0.0.0.3 area 0

FT_WORTH#show run!router ospf 1network 192.168.2.0 0.0.0.255 area 0network 192.168.240.0 0.0.0.3 area 0

!router ripnetwork 192.168.224.0

ANAHEIM#show run!router ripnetwork 192.168.1.0network 192.168.224.0


Configure FtWorth to redistribute routes

• Since FtWorth is the ASBR, we configure it to redistribute the RIP routes into OSPF.

• The redistributecommand has different parameters, depending on the routing process.

Enter redistribute ? to see all the different parameters.



• Specify rip as the protocol to redistribute.

• Since the WAN link between Anaheim and FtWorth is a subnet, specify the parameter subnet.

If the parameter subnet is not configured, the WAN link will not be advertised.

FT_WORTH#show run!router ospf 1redistribute rip subnetsnetwork 192.168.2.0 0.0.0.255 area 0network 192.168.240.0 0.0.0.3 area 0


Verify Redistribution of RIP routesRICHMOND#show ip route










O E2 192.168.224.0 [110/20] via 192.168.240.1, 00:19:02, Serial0/1



O E2 192.168.1.0/24 [110/20] via 192.168.240.1, 00:39:37, Serial0/1

O 192.168.2.0/24 [110/65] via 192.168.240.1, 00:39:37, Serial0/1


E2 means that OSPF will propagate this external route with the same cost (defaults to 20) throughout the OSPF routing domain.


Redistribution of a Default Route

• To finish our configuration, we need a default route point to Richmond.

• Then we need to redistribute that default route to Anaheim.

Default RouteRedistribute

Default Route



• The default-information originate command instructs the IOS to propagate the default route to RIP routers.

• The default route is redistributed into the RIP routing process and tagged as a default route.

• NOTE: A bug in the IOS may require a reload before the default route is redistributed.

FT_WORTH#show run!router ripdefault-information originate

!ip route 0.0.0.0 0.0.0.0 192.168.240.2


Default Route


Verify FtWorth is tagging the default route

FtWorth#show ip route








Gateway of last resort is 192.168.240.2 to network 0.0.0.0





R 192.168.1.0/24 [120/1] via 192.168.224.1, 00:00:02, Serial0/0


O 192.168.3.0/24 [110/65] via 192.168.240.2, 00:05:33, Serial0/1

S* 0.0.0.0/0 [1/0] via 192.168.240.2


Default Route


Verify Anaheim has a default route

Anaheim#show ip route












R* 0.0.0.0/0 [120/1] via 192.168.224.2, 00:00:09, Serial0/0


Default Route


eLab: RIP and OSPF Redistribution




• Once you access the menu of activities, choose the “RIP and OSPF Redistribution” activity.



Example 3:Redistributing EIGRP and OSPF


Overview of EIGRP and OSPF Redistribution

• Just like RIP and OSPF, we can redistribute between EIGRP and OSPF.

• In our scenario, FtWorth will redistribute OSPF routes into the EIGRP routing process shared with Anaheim

• FtWorth will also redistribute a default route to Richmond.

RedistributeDefault RouteDefault Route


Basic routing configurations• Notice that FtWorth is

configured with both OSPF and EIGRP.


RICHMOND#show run!router ospf 1network 192.168.3.0 0.0.0.255 area 0network 192.168.240.0 0.0.0.3 area 0

FT_WORTH#show run!router ospf 1network 192.168.240.0 0.0.0.3 area 0

!router eigrp 100network 192.168.2.0network 192.168.224.0no auto-summary

ANAHEIM#show run!router eigrp 100network 192.168.1.0network 192.168.224.0no auto-summary


The redistribute command and EIGRP

• EIGRP uses a composite metric to calculate the best route. The metrics are...

Bandwidth, Delay, Load, Reliability, and MTU

• By default, only bandwidth and delay are evaluated.

• However, when configuring redistribution we configure all five metric values.

This can be done by adding parameters to the redistribute command (shown below) or separately, using the default-metric command (shown later).

Router(config)#router eigrp 100Router(config-router)#redistribute protocol metric bandwidth

delay reliability load MTU


The redistribute command and EIGRP

• The metric values are explained below:bandwidth is minimum the bandwidth of the route in kbps (1544 in our example)delay is the delay in tens of microseconds (200 in our example)reliability is 1 to 255 where 255 is 100% reliable (we will use 255)load is 1 to 255 where 255 is 100% loaded (we will use 1)

MTU is maximum transmission unit in bytes. We will use 1500 since this is Ethernet’s MTU size.

Router(config)#router eigrp 100Router(config-router)#redistribute protocol metric bandwidth

delay reliability load MTU



• Enter the command on FtWorthwithin the EIGRP routing process and verify redistribution on Anaheim. Redistribute

Default RouteDefault Route

FT_WORTH#show run!router eigrp 100redistribute ospf 1 metric 1544 200 255 1 1500

Anaheim#show ip route

<output omitted>




D EX 192.168.240.0 [170/2221056] via 192.168.224.2, 00:00:15, Serial0/0


D 192.168.2.0/24 [90/2172416] via 192.168.224.2, 01:04:34, Serial0/0

D EX 192.168.3.0/24 [170/2221056] via 192.168.224.2, 00:00:15, Serial0/0

D EX means that these routes are external EIGRP routes. Note that administrative distance is 170.



• Just like with RIP, the default-information originate command instructs the IOS to propagate the default route to OSPF routers.

FT_WORTH#show run!router ospf 1default-information originate

!ip route 0.0.0.0 0.0.0.0 192.168.224.1



Verify FtWorth is tagging the default route

FT_WORTH#show ip route













D 192.168.1.0/24 [90/2172416] via 192.168.224.1, 05:45:43, Serial0/0


O 192.168.3.0/24 [110/65] via 192.168.240.2, 00:00:12, Serial0/1

S* 0.0.0.0/0 [1/0] via 192.168.224.1



Verify Richmond has a default route

Richmond#show ip route












O*E2 0.0.0.0/0 [110/1] via 192.168.240.1, 00:01:12, Serial0/1



eLab: EIGRP and OSPF Redistribution




• Once you access the menu of activities, choose the “EIGRP and OSPF Redistribution” activity.



Resources

• Download this PowerPoint and all the eLabs in one zip filehttp://johnsontraining.com/CCNP_v3/CCNP1/Module08

• Ask the Expert Series: Route Redistribution• Cisco.com’s Internetwork Design Guide

RIP and OSPF RedistributionIntegrating EIGRP into Existing Networks

• CCNP1, v3.0 CurriculumModule 8: Route Optimization

• E-Lab ComposerDowload from Academy Connection

Forums & Chat >> CCNA >> E-Lab Composer under “Instructor Quick Links”

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