RIP version 1 - College of DuPage · RIP version 1 Routing Protocols and Concepts ... Cisco Public...

© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

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Chapter 1 1

RIP version 1

Routing Protocols and Concepts – Chapter 5

Modified by Tony Chen

06/10/2008

ITE PC v4.0

Chapter 1 2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Objectives Describe the functions, characteristics, and operation

of the RIPv1 protocol.

Configure a device for using RIPv1.

Verify proper RIPv1 operation.

Describe how RIPv1 performs automatic summarization.

Configure, verify, and troubleshoot default routes propagated in a routed network implementing RIPv1.

Use recommended techniques to solve problems related to RIPv1

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RIP Historical Impact RIP evolved from an earlier protocol

developed at Xerox, called Gateway Information Protocol (GWINFO).

With the development of Xerox Network System (XNS), GWINFO evolved into RIP.

It later gained popularity because it was implemented in the Berkeley Software Distribution (BSD) as a daemon named routed (pronounced "route-dee", not "rout-ed").

Recognizing the need for standardization of the protocol, Charles Hedrick wrote RFC 1058 in 1988, in which he documented the existing protocol and specified some improvements.

Since then, RIP has been improved with RIPv2 in 1994 and with RIPng in 1997. IPv6 form of RIP called

RIPng (next generation) is now available

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RIPv1

RIP Characteristics

–A classful, Distance Vector (DV) routing protocol

–Metric = hop count

–Routes with a hop count > 15 are unreachable

–Updates are broadcast every 30 seconds

–The data portion of a RIP message is encapsulated into a UDP segment, with both source and destination port numbers set to 520.

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RIPv1 RIP Message Format

RIP header - divided into 3 fields

–Command field•REQUEST (1)- Request either a partial or full table update from another RIP router.

•RESPONSE (2) - A response to a request.

–Version field

•1 or 2

–Must be zero

•Must be zero" fields provide room for future expansion of the protocol.

Route Entry - composed of 3 fields

–Address family identifier

•CLNS, IPX, IP etc.

–IP address

–Metric

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RIPv1

RIP Operation

–RIP uses 2 message types:

Request message

-This is sent out on startup by each RIP enabled interface

-Requests all RIP enabled neighbors to send routing table

Response message

-Message sent to requesting router containing routing table

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RIPv1

IP addresses initially divided into classes

-Class A

-Class B

-Class C

RIP is a classful routing protocol

-Does not send subnet masks in routing updates

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Common RIP configuration issues

RIP and IGRP:

Classful network statements only

IOS will take subnetted networks but will translate it into the classful network for the running-config.

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RIPv1

Administrative Distance

–RIP’s default administrative distance is 120

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Basic RIPv1 Configuration A typical topology suitable for

use by RIPv1 includes:

-Three router set up

-No PCs attached to LANs

-Use of 5 different IP subnets

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Basic RIPv1 Configuration

Router RIP Command

–To enable RIP enter:

-Router rip at the global configuration prompt

-Prompt will look like R1(config-router)#

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Basic RIPv1 Configuration

Specifying Networks

–Use the networkcommand to:

-Enable RIP on all interfaces that belong to this network

-Advertise this network in RIP updates sent to other routers every 30 seconds

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Verification and Troubleshooting

Show ip Route

To verify and troubleshoot routing

-Use the following

commands:

-show ip route

-show ip protocols

-debug ip rip

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show ip protocolscommand

-Displays routing protocol configured on router

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Verification and Troubleshooting Debug ip rip command

-Used to display RIP routing updates as they are happening

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Passive interface command

-Used to prevent a router from sending updates through an interface

-Example:

Router(config-router)#passive-interface interface-type interface-number

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Verification and Troubleshooting Passive interfaces

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Preventing routing updates through an interface

Route filtering works by regulating the routes that are entered into or advertised out of a route table.

As a result, a route filter influences which routes the router advertises to its neighbors.

On the other hand, routers running link state protocols determine routes based on information in the link-state database. Route filters have no effect on link-state advertisements or the link-state database.

(Tony) Route filtering could have negative effect on the link-state routing protocol.

Using the passive interface command can prevent routers from sending routing updates through a router interface, but the router continues to listen and use routing updates from that neighbor.

Keeping routing update messages from being sent through a router interface prevents other systems on that network from learning about routes dynamically.

Lab:

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Preventing routing updates through an interface

Again, this is only half the story.

When you use “passive interface” on a distance vector routing protocol, you need to complement it with “ip route” command.

You can not use “passive interface” command on link state routing protocol.

Because you just kill the “keep alive” or “hello” packet.

It will break the rip update

You can use the “ip route”

command to send route update

back to establish the 2 way

communication

1

2

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Automatic Summarization Modified Topology

The original scenario has been modified such that:

Three classful networks are used:

172.30.0.0/16

192.168.4.0/24

192.168.5.0/24

The 172.30.0.0/16 network is subnetted into three subnets:

172.30.1.0/24

172.30.2.0/24

172.30.3.0/24

The following devices are part of the 172.30.0.0/16 classful network address:

All interfaces on R1

S0/0/0 and Fa0/0 on R2

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Automatic Summarization

Configuration Details

-To remove the RIP routing process use the following command

No router rip

-To check the configuration use the following command

Show run

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Automatic Summarization Boundary Routers

–RIP automatically summarizes classful networks

–Boundary routers summarize RIP subnets from one major network to another.

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Processing RIP Updates

2 rules govern RIPv1 updates:

-If a routing update and the interface it’s received on belong to the samenetwork then

The subnet mask of the interface is applied to the network in the routing update

-If a routing update and the interface it’s received on belong to a differentnetwork then

The classful subnet mask of the network is applied to the network in the routing update.

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Sending RIP Updates

–RIP uses automatic summarization to reduce the size of a routing table.

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Advantages of automatic summarization:

-The size of routing updates is reduced

-Single routes are used to represent multiple routes which results in faster lookup in the routing table.

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Automatic Summarization Disadvantage of Automatic Summarization:

-Does not support discontiguous networks

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Discontiguous Topologies do not converge with RIPv1

A router will only advertise major network addresses out interfaces that do not belong to the advertised route.

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Default Route and RIPv1

Modified Topology: Scenario C

Default routes

Packets that are not defined specifically in a routing table will go to the specified interface for the default route

Example: Customer routers use default routes to connect to an ISP router.

Command used to configure a default route is

ip route 0.0.0.0 0.0.0.0 s0/0/1

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Propagating the Default Route in RIPv1

Default-information originate command

-This command is used to specify that the router is to originate default information, by propagating the static default route in RIP update.

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Default route with RIP

Centre#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,

Gateway of last resort is not set

R 192.168.4.0/24 [120/1] via 192.168.2.1, 00:00:11, Serial0

R 192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:11, Serial0

C 192.168.2.0/24 is directly connected, Serial0

C 192.168.3.0/24 is directly connected, Ethernet0

Mobile#sho ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,

Gateway of last resort is not set

R 192.168.4.0/24 [120/1] via 192.168.1.1, 00:00:04, Serial0



R 192.168.2.0/24 [120/1] via 192.168.1.1, 00:00:04, Serial0

R 192.168.3.0/24 [120/2] via 192.168.1.1, 00:00:04, Serial0

Centre(config)#ip route 0.0.0.0 0.0.0.0 loopback0

Setup up a default route on the Centre router

Centre(config)#router rip

Centre(config-router)#default-information originate

Centre#sh ip route

Codes: C - connected, S - static, * - candidate default

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

C 172.16.1.1 is directly connected, Loopback0

R 192.168.4.0/24 [100/8576] via 192.168.2.1, 00:00:22, Serial0

R 192.168.5.0/24 [120/2] via 192.168.2.1, 00:00:22, Serial0

S* 0.0.0.0/0 is directly connected, Loopback0

Mobile#sho ip route

Codes: C - connected, S - static, * - candidate default - RIP,

Gateway of last resort is 192.168.1.1 to network 0.0.0.0

R 192.168.4.0/24 [120/1] via 192.168.1.1, 00:00:09, Serial0



R 192.168.2.0/24 [120/1] via 192.168.1.1, 00:00:04, Serial0

R 192.168.3.0/24 [120/2] via 192.168.1.1, 00:00:09, Serial0

R* 0.0.0.0/0 [120/2] via 192.168.1.1, 00:00:09, Serial0

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Summary

RIP characteristics include:

Classful, distance vector routing protocol

Metric is Hop Count

Does not support VLSM or discontiguous subnets

Updates every 30 seconds

Rip messages are encapsulated in a UDP segment with source and destination ports of 520

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Summary: Commands used by RIP

Command Command’s purpose

Rtr(config)#router rip Enables RIP routing process

Rtr(config-router)#network Associates a network with a RIP routing process

Rtr#debug ip rip used to view real time RIP routing updates

Rtr(config-router)#passive-interface fa0/0 Prevent RIP updates from going out an interface

Rtr(config-router)#default-information originate Used by RIP to propagate default routes

Rtr#show ip protocols Used to display timers used by RIP

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