RIP version 1

© 2007 Cisco Systems, Inc. All rights reserved. Cisco PublicITE PC v4.0Chapter 1 1

RIP version 1

Routing Protocols and Concepts – Chapter 5

Sandra Coleman, CCNA, CCAI

ITE PC v4.0Chapter 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

Turquoise text is test-worthy!


RIPv1 RIP Characteristics

-Oldest distance vector protocol

-A classful, Distance Vector (DV) routing protocol

-Metric = hop count

-Routes with a hop count > 15 are unreachable

-16 hops = infinity

-Updates are broadcast every 30 seconds

-Calculates metrics using the Bellman Ford algorithm

-Data portion is encapsulated into UDP segment


RIPv1 RIP Message Format RIP header - divided into

3 fields

-Command field

-Version field

-Must be zero Route Entry - composed

of 3 fields -Address family identifier -IP address-Metric (hops)

RIPv2 uses most of the ‘must be zero’ space


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


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

-A router either uses the SM configure on the local interface or applies the default subnet mask of the class

-Can’t support discontiguous networks or VLSM


RIPv1 Administrative Distance

–RIP’s default AD is 120 which makes it the least-preferred routing protocol (all others have a lower AD)


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


Basic RIPv1 Configuration

Router RIP Command

–To enable RIP enter:

-Router rip at the global configuration prompt

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

Notice that typing Router ? At the

promptWill show you

ALLAvailable routing

protocols


Removing RIP

To completely remove RIP routing from a router, just type in the following command:

router(config)#no router rip

This command will STOP all rip processes and erase all existing RIP configurations!


Basic RIPv1 Configuration Specifying Networks (You have to

be able to do this on the test!)

–Use the network command to:

-Enable RIP on all interfaces that belong to this network

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

-If you enter an IP address instead of a network address, RIP will include all interfaces in that CLASSFUL network in the routing process


Verification and Troubleshooting To verify and

troubleshoot routing

-Use the following commands:

-show ip route

-show ip protocols-debug ip rip


Routing tables You will have to look at a topology and pick from a list

routes that would appear in a routing table for a specific router in that topology. One thing you really need to pay attention to is whether it is a connected or RIP route and look at the metric…make sure it is correct!


Verification and Troubleshooting

show ip protocols command

-Displays routing protocol configured on router

Be able to interpret these on a test!


Marking invalid routesRefer to the routing table below. Notice the timer SINCE the last update. How long would it take to mark 192.168.1.0 INVALID if it went down? Invalid timer is 180 seconds. Subtract the time since the last update (5 seconds) and you get the answer! You will have to do this on the test as well!


Verification and Troubleshooting Debug ip rip command (5.3.3 – online curriculum)

-Used to display RIP routing updates as they are happening - USE undebug all to turn off ALL debugging!


Verification and Troubleshooting Passive interface command

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

-Example:

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

Router(config-router)#passive-interface fa 0/0

When would you use this command? If you have an interface that has only END-USERS (LAN-Ethernet connection) connected, there is no need to broadcast routing updates to end-users. It WASTES bandwidth!

We only need to send routing update out interfaces where OTHER routers are found…but we do want the LANS to be included in the updates.

Passive interface prevents the transmission of routing updates through a router interface but still allows that network to be advertised to other routers


Verification and Troubleshooting Passive interfaces


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 R1S0/0/0 and Fa0/0 on R2


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


Automatic Summarization Boundary Routers

–RIP automatically summarizes classful networks

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

–Because boundary routers summarize RIP subnets from one major network to the other, updates for the 172.30.1.0, 172.30.2.0 and 172.30.3.0 networks will automatically be summarized into 172.30.0.0 when sent out R2's Serial 0/0/1 interface.


Automatic SummarizationProcessing RIP Updates

2 rules govern RIPv1 updates:

-If a routing update and the interface it’s received on belong to the same network 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 different network then The classful subnet mask of the network is applied to the network in the routing update.

RIPv1 DOES NOT send subnet mask information in its updates!


Automatic Summarization Sending RIP Updates

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


Automatic Summarization

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.


Automatic Summarization Disadvantage of Automatic Summarization:

-Does not support discontiguous networks


Automatic Summarization 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.


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 (AKA Gateway of last resort)

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


Default Route and RIPv1


Default Route and RIPv1 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.

Indicates a ‘default –

information originate’ command from R2


Where to put default routes? Default routes (0.0.0.0) and the ability to propagate

these routes to others lies with the border router.

What is a border router? It is the router in your company that connects to your ISP.

So these commands belong on the border router! ip route 0.0.0.0 0.0.0.0 s0/0/1

Default-information originate

You should NEVER exchange routing updates with an ISP. You only set up a static route to them. Otherwise, you end up with a HUGE routing table, and all outgoing traffic still goes there anyway!


Equal Cost Paths

When you see routing table entries that have the same network listed with 2 different outgoing interfaces…know that these are 2 EQUAL COST PATHS.


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

Date post:	22-Jan-2016
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