ccna e2 05 ripv1

RIP Version 1

Routing Protocols and Concepts – Chapter 5

Richard L. Holladay, CCNA, Ph.D.

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Topics

RIPv1: A Distance Vector, Classful Routing Protocol

Background and Perspective

RIPv1 Characteristics and Message Format

RIP Operation

Basic RIPv1 Configuration

RIPv1: Scenario A

Enable RIP: router rip Command

Specifying Networks

Verification and Troubleshooting

Verifying RIP: show ip route

Verifying RIP: show ip protocols

Verifying RIP: debug ip rip

Passive Interfaces

Automatic Summarization

Modified Topology: Scenario B

Boundary Routers and Automatic Summarization

Processing RIP Updates

Sending RIP Updates

Advantages and Disadvantages of Automatic Summarization

Default Route and RIPv1

Modified Topology: Scenario C

Propagating the Default Route in RIPv1

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RIPv1

Download Packet Tracer Topology: RIPv1-A-student.pkt on my website to use for configuration practice with lecture.

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RIPv1: Distance Vector, Classful Routing Protocol

Why learn RIP?

Still in use today.

Helps to understand fundamental concepts and comparisons of protocols

Classful (RIPv1) vs classless (RIPv2)

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RIP is not a protocol “on the way out.”

In fact, an IPv6 form of RIP called RIPng (next generation) is now available.

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Charles Hedrick wrote RFC 1058 in 1988, in which he documented the existing protocol and specified some improvements.

RFC 1058 can be found at http://www.ietf.org/rfc/rfc1058.txt

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RIP characteristics:

Distance Vector or Link State?

Distance vector routing protocol.

Metric?

Hop count

Maximum Hop count?

Greater than 15 is considered unreachable.

Routing table updates are broadcast every…?

30 seconds. (RIPv2 uses multicasts)

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IP Address Classes and Classful Routing

RIPv1:

Classful routing protocol.

Does not send subnet mask in update.

No subnet mask

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IP Address Classes and Classful Routing

R2 receives an RIP update with a network address.

R2 adds the network address and determines which mask to add to the routing table because no mask is passed with the update.

It can only uses either the subnet mask of the:

Local interface or

The default classful subnet mask (…more later!)

Because of this mask limitation, RIPv1 networks cannot be discontiguous, nor can they implement VLSM.

RIP Update network-add

Routing TableNetwork-add/mask

/16

?172.30.2.1/24

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RIPv1 is a classful or classless routing protocol?

Classful

How many classful networks are there and of what class?

5 Class C network addresses.

We will see that the class of the network is used by RIPv1 to determine the subnet mask.

RIPv1 Scenario A

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5

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Enabling RIP: router rip Command (don’t do this yet)

What routing protocols does this router support? (PT is limited)

Configure RIP…

R1# conf tEnter configuration commands, one per line. End with CNTL/Z.R1(config)# router ?bgp Border Gateway Protocol (BGP)egp Exterior Gateway Protocol (EGP)

eigrp Enhanced Interior Gateway Routing Protocol (EIGRP)igrp Interior Gateway Routing Protocol (IGRP)isis ISO IS-IS

iso-igrp IGRP for OSI networksmobile Mobile routes

odr On Demand stub Routesospf Open Shortest Path First (OSPF)

rip Routing Information Protocol (RIP)R1(config)# router ripR1(config-router)#

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Enabling RIP: router rip Command (don’t do this yet)

no router rip

To remove the RIP routing process from a device

Stops the RIP process

Erases all existing RIP configuration commands.

R1# conf tR1(config)# router ripR1(config-router)# network 192.168.1.0R1(config-router)# network 192.168.2.0R1(config-router)# exitR1(config)# no router rip

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To enable RIP routing for a network, use the network command in router configuration mode

Enter the classful network address for each directly connected network.

Router(config-router)# network directly-connected-classful- network-address

Specifying Networks

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The network command performs the following functions:

Enables RIP on all interfaces that belong to a specific network.

Associated interfaces will now both send and receive RIP updates.

Advertises the specified network in RIP routing updates sent to other routers every 30 seconds (no mask).

R1(config)# router ripR1(config-router)# network 192.168.1.0R1(config-router)# network 192.168.2.0

Specifying Networks

RIP Update

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Specifying Networks

Configure RIP for all three routers

What happens if you enter a subnet or host IP address? (Try it)

IOS automatically converts it to a classful network address.

For example, if you enter the command network 192.168.1.32, the router will convert it to network 192.168.1.0.


R2(config)# router ripR2(config-router)# network 192.168.2.0R2(config-router)# network 192.168.3.0R2(config-router)# network 192.168.4.0


Only directly connected classful network addresses!

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Only directly connected classful network addresses!

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Administrative Distance

What is the administrative distance of a network route learned via RIP?

120

R3# show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP,

<some output omitted>

* - candidate default, U - per-user static route, o - ODRP - periodic downloaded static route

Gateway of last resort is not set

R 192.168.1.0/24 [120/2] via 192.168.4.2, 00:00:13, Serial0/0/1

R 192.168.2.0/24 [120/1] via 192.168.4.2, 00:00:25, Serial0/0/1R 192.168.3.0/24 [120/1] via 192.168.4.2, 00:00:25, Serial0/0/1

C 192.168.4.0/24 is directly connected, Serial0/0/1C 192.168.5.0/24 is directly connected, FastEthernet0/0

R3#

R = RIP

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Administrative Distance

Where is the administrative distance displayed using this command?

R3# show ip protocols<output omitted>Routing Protocol is “rip”

Routing Information Sources:Gateway Distance Last Update

192.168.6.2 120 00:00:10Distance: (default is 120)

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Verifying RIP: show ip route on all three routers…

R1# show ip routeCodes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,<output omitted>


R 192.168.4.0/24 [120/1] via 192.168.2.2, 00:00:02, Serial0/0/0R 192.168.5.0/24 [120/2] via 192.168.2.2, 00:00:02, Serial0/0/0C 192.168.1.0/24 is directly connected, FastEthernet0/0

C 192.168.2.0/24 is directly connected, Serial0/0/0R 192.168.3.0/24 [120/1] via 192.168.2.2, 00:00:02, Serial0/0/0

The routing table, includes what kind of routes?

Directly connected networks

Static routes

Dynamic routes

Why might a RIP route not be immediately displayed in the routing table?

Networks will take some time to converge.

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Verifying RIP: show ip route Command



C 192.168.4.0/24 is directly connected, Serial0/0/1R 192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:12, Serial0/0/1R 192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0

C 192.168.2.0/24 is directly connected, Serial0/0/0C 192.168.3.0/24 is directly connected, FastEthernet0/0

Using R2, which routes do you expect to see in our scenario?

Directly connected networks of R2

RIP routes for remote networks

What routes do you expect not to see?

Networks not in our scenario – not configured with network statements on the routers.

Static default route

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C 192.168.4.0/24 is directly connected, Serial0/0/1C 192.168.5.0/24 is directly connected, FastEthernet0/0R 192.168.1.0/24 [120/2] via 192.168.4.2, 00:00:08, Serial0/0/1

R 192.168.2.0/24 [120/1] via 192.168.4.2, 00:00:08, Serial0/0/1R 192.168.3.0/24 [120/1] via 192.168.4.2, 00:00:08, Serial0/0/1

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R1# show ip route<output omitted>R 192.168.5.0/24 [120/2] via 192.168.2.2, 00:00:23, Serial0/0/0

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R1# show ip route<output omitted>R 192.168.5.0/24 [120/2] via 192.168.2.2, 00:00:23, Serial0/0/0

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Examine and discuss the show ip protocols Command

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Verifying RIP: show ip protocols Command

Verifies that RIP routing is configured and running on Router R2

At least one active interface with an associated network command is needed before RIP routing will start.

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These are the timers that show when the next round of updates will be sent out from this router—23 seconds from now, in the example.

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This information relates to filtering updates and redistributing routes, if configured on this router.

Filtering and redistribution are both CCNP-level topics.

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Information about which RIP version is currently configured and which interfaces are participating in RIP updates.

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Router R2 is currently summarizing at the classful network boundary

By default, will use up to four equal-cost routes to load- balance.

Automatic summarization is discussed later in this chapter.

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Classful networks configured with the network command are listed next.

These are the networks that R2 will include in its RIP updates. (with other learned routes)

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RIP neighbors

Gateway: Next-hop IP address of the neighbor that is sending R2 updates.

Distance is the AD that R2 uses for updates sent by this neighbor.

Last Update is the seconds since the last update was received from this neighbor.

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Use debug ip rip to view RIP updates that are sent and received…

The debug command is a useful tool to help diagnose and resolve networking problems, providing real-time, continuous information.

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Assuming all routers have converged, why were no other routes from R1’s routing table sent to R2?

Split horizon rule.

R1 will not advertise networks back to R2 that were learned from R2.

RIP: received v1 update from 192.168.2.1 on Serial0/0/0192.168.1.0 in 1 hops

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RIP: received v1 update from 192.168.4.1 on Serial0/0/1192.168.5.0 in 1 hops

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RIP: sending v1 update to 255.255.255.255 via FastEthernet0/0(192.168.3.1)

RIP: build update entriesnetwork 192.168.1.0 metric 2network 192.168.2.0 metric 1network 192.168.4.0 metric 1network 192.168.5.0 metric 2

Directly Connected

Learned via RIP from R1


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RIP: sending v1 update to 255.255.255.255 via Serial0/0/1(192.168.4.2)

RIP: build update entriesnetwork 192.168.1.0 metric 2network 192.168.2.0 metric 1network 192.168.3.0 metric 1

Directly Connected


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RIP: sending v1 update to 255.255.255.255 via Serial0/0/0(192.168.2.2)

RIP: build update entriesnetwork 192.168.3.0 metric 1network 192.168.4.0 metric 1network 192.168.5.0 metric 2

Directly Connected


R2# undebug allAll possible debugging has been turned off

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Does R2 need to send RIP updates out Fa 0/0?

No, there is no RIP router or any router.

Bandwidth is wasted transporting unnecessary updates.

All devices on the LAN must process the RIPv1 update up to the transport layer.

Security risk (Authentication would is a better solution - later)

Passive InterfacesGot Router?

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Passive Interfaces

What about using this command on R2?R2(Config-router)# no network 192.168.3.0

This would keep R2 from advertising this LAN as a route in updates it sends to R1 and R3.

Correct solution is to use the passive-interface command

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

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Passive Interfaces – Use it on R2…

R2(config)# router ripR2(config-router)# passive-interface FastEthernet 0/0

X

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Passive InterfacesR2# show ip protocols<output omitted>

Interface Send Recv Triggered RIP Key-chain

Serial0/0/0 1 1 2Serial0/0/1 1 1 2

Automatic network summarization is in effectRouting for Networks:

192.168.2.0

192.168.3.0192.168.4.0

Passive Interface(s):FastEthernet0/0

Routing Information Sources:Gateway Distance Last Update192.168.2.1 120 00:00:27

192.168.4.1 120 00:00:23Distance: (default is 120)

FastEthernet 0/0 no longer included

LAN network still included in RIP updates that are sent

FastEthernet 0/0 is a passive interface

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Where is the separation of classful networks?

Summarizing several routes into a single route is known as route summarization or route aggregation.

Fewer routes = smaller routing tables = faster lookups

Some routing protocols, such as RIP, automatically summarize routes on certain routers.

172.30.0.0/16

192.168.4.0/24

192.168.5.0/24

.10

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What are the classful networks?

172.30.0.0/16

192.168.4.0/24

192.168.5.0/24

How is 172.30.0.0/16 network subnetted?

172.30.1.0/24

172.30.2.0/24

172.30.3.0/24

Is 192.168.4.0/24 subnetted?

192.168.4.8/30.

172.30.0.0/16

192.168.4.0/24

192.168.5.0/24

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Configuration Changes for R1

R1(config)# interface fa0/0R1(config-if)# ip address 172.30.1.1 255.255.255.0R1(config-if)# interface S0/0/0R1(config-if)# ip address 172.30.2.1 255.255.255.0R1(config-if)# no router ripR1(config)# router ripR1(config-router)# network 172.30.1.0R1(config-router)# network 172.30.2.0R1(config-router)# passive-interface FastEthernet 0/0R1(config-router)# endR1# show run<output omitted>

!router rippassive-interface FastEthernet0/0

network 172.30.0.0!

<output omitted>

IOS automatically corrects subnet entries to classful network address

The no shutdown and clock rate commands are not needed because these commands are still configured from Scenario A.

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Configuration Changes for R2R2(config)# interface S0/0/0R2(config-if)# ip address 172.30.2.2 255.255.255.0R2(config-if)# interface fa0/0R2(config-if)# ip address 172.30.3.1 255.255.255.0R2(config-if)# interface S0/0/1R2(config-if)# ip address 192.168.4.9 255.255.255.252R2(config-if)# no router ripR2(config)# router ripR2(config-router)# network 172.30.0.0R2(config-router)# network 192.168.4.8R2(config-router)# passive-interface FastEthernet 0/0R2(config-router)# endR2# show run<output omitted>!

router rippassive-interface FastEthernet0/0

network 172.30.0.0network 192.168.4.0! <output omitted>

IOS automatically corrects subnet entries to classful network address

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Configuration Changes for R3

R3(config)# interface fa0/0R3(config-if)# ip address 192.168.5.1 255.255.255.0R3(config-if)# interface S0/0/1R3(config-if)# ip address 192.168.4.10 255.255.255.252R3(config-if)# no router ripR3(config)# router ripR3(config-router)# network 192.168.4.0R3(config-router)# network 192.168.5.0R3(config-router)# passive-interface FastEthernet 0/0R3(config-router)# endR3# show run<output omitted>

!router rippassive-interface FastEthernet0/0

network 192.168.4.0network 192.168.5.0

!<output omitted>

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RIP is a classful routing protocol that automatically summarizes classful networks across major network boundaries.

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Does R2 have interfaces on more than one major classful network?

Yes, 172.30.0.0 and 192.168.4.0

This makes R2 a boundary router in RIP.

Boundary routers summarize RIP subnets from one major network to the other:

172.30.1.0, 172.30.2.0, and 172.30.3.0 networks automatically summarized into 172.30.0.0 when sent out R2’s Serial 0/0/1 interface.

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Do Classful routing protocols such as RIPv1 include the subnet mask in the routing update.

No.

So how does a router running RIPv1 determine what subnet mask it should apply to a route when adding it to the routing table?

R2# show ip route172.30.0.0/24 is subnetted, 3 subnets

R 172.30.1.0 [120/1] via 172.30.2.1, 00:00:18, Serial0/0/0

C 172.30.2.0 is directly connected, Serial0/0/0C 172.30.3.0 is directly connected, FastEthernet0/0

192.168.4.0/30 is subnetted, 1 subnetsC 192.168.4.8 is directly connected, Serial0/0/1R 192.168.5.0/24 [120/1] via 192.168.4.10, 00:00:16, Serial0/0/1

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Rules for Processing RIPv1 Updates

The following two rules govern RIPv1 updates:

If a routing update and the interface on which it is received belong to the same major network, the subnet mask of the interface is applied to the network in the routing update.

If a routing update and the interface on which it is received belong to different major networks, the classful subnet mask of the network is applied to the network in the routing update..

Routing Update and Interface Routing Update Subnet MaskSame Classful Major Network Use mask of interfaceDifferent Classful Major Network Use default classful mask

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Example of RIPv1 Processing Updates

Same classful network as the incoming update.

Update: 172.30.1.0 in 1 hops

Interface received:

Serial 0/0/0 - 172.30.2.2/24

Same classful network address (172.30.0.)

Applies subnet mask of its S0/0/0 interface, /24.

The 172.30.1.0 /24 subnet was added to the routing table.

R2# debug ip rip (selected output)RIP: received v1 update from 172.30.2.1 on Serial0/0/0

172.30.1.0 in 1 hops

R2# show ip route (selected output)172.30.0.0/24 is subnetted, 3 subnets

R 172.30.1.0 [120/1] via 172.30.2.1, 00:00:18, Serial0/0/0

172.30.1.0

172.30.2.2/24

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R2# debug ip ripRIP protocol debugging is onRIP: sending v1 update to 255.255.255.255 via Serial0/0/0 (172.30.2.2)RIP: build update entries

network 172.30.3.0 metric 1network 192.168.4.0 metric 1network 192.168.5.0 metric 2

RIP: sending v1 update to 255.255.255.255 via Serial0/0/1 (192.168.4.9)RIP: build update entries

network 172.30.0.0 metric 1

Sending RIP Updates

192.168.4.0/24

192.168.5.0/24

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Sending RIP Updates172.30.3.0192.168.4.0192.168.5.0 172.30.0.0

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Determining the Mask and Network Address

Receiving an Update: Determining subnet mask for routing table

What is the major classful network address of the receiving interface?

What is the major classful network address of the network in the routing update?

Are they the same major classful network address?

Yes: Apply subnet mask of the receiving interface for this network address in the routing table.

No: Apply classful subnet mask for this network address in the routing table.

Sending an Update: Determining whether or not to summarize route sent

What is the major classful network address of the sending interface?

What is the major classful network address of the network in the routing update?

Are they the same major classful network address?

Yes: Send subnet network address

No: Send summary address – the classful network address

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Verifying Routing Updates

R1# show ip route<output omitted>Gateway of last resort is not set

172.30.0.0/24 is subnetted, 3 subnetsC 172.30.1.0 is directly connected, FastEthernet0/0C 172.30.2.0 is directly connected, Serial0/0/0R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:17, Serial0/0/0R 192.168.4.0/24 [120/1] via 172.30.2.2, 00:00:17, Serial0/0/0R 192.168.5.0/24 [120/2] via 172.30.2.2, 00:00:17, Serial0/0/0

R3# show ip route<output omitted>Gateway of last resort is not setR 172.30.0.0/16 [120/1] via 192.168.4.9, 00:00:15, Serial0/0/1

192.168.4.0/30 is subnetted, 1 subnetsC 192.168.4.8 is directly connected, Serial0/0/1C 192.168.5.0/24 is directly connected, FastEthernet0/0

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Classful Routing Protocols Do Not Support VLSM

Routers running RIPv1 are limited to using the same subnet mask for all subnets with the same classful network.

Classless routing protocols such as RIPv2 allow the same major (classful) network to use different subnet masks (VLSM).

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Advantages of Automatic Summarization

Smaller routing updates

R3# show ip route<output omitted>Gateway of last resort is not setR 172.30.0.0/16 [120/1] via 192.168.4.9, 00:00:15, Serial0/0/1


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What Networks Get Summarized?

172.16.0.0/16 is a Class B network subnetted into /24 subnets.

Routers with interfaces in the same 172.16.0.0/24 subnetted network share their 172.16.0.0 subnets and apply the /24 subnet mask of their receiving interface.

There is no summarization – all routers know about all 172.16.0.0 subnets.

172.16.10.0/24

172.16.12.0/24

172.16.11.0/24

172.16.13.0/24

172.16.1.0/24

172.16.20.0/24 172.16.22.0/24

172.16.21.0/24 172.16.23.0/24

172.16.2.0/24

172.16.100.0/24

172.16.101.0/24

172.16.102.0/24

172.16.103.0/24

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R3 summarizes 172.16.0.0/24 subnets as 172.16.0.0 because 10.0.0.0/30 is a different network (10.0.0.0 class A network).

R3 knows this because it has an interface IP address on the 10.0.0.0/8 network.

RE applies the default class B subnet mask /16 to the 172.16.0.0 network.

172.16.10.0/24

172.16.12.0/24

172.16.11.0/24

172.16.13.0/24

172.16.1.0/24

172.16.20.0/24 172.16.22.0/24

172.16.21.0/24 172.16.23.0/24

172.16.2.0/24

INTERNET

10.0.0.0/30

172.16.0.0


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Routers with interfaces in the same 172.18.0.0/24 subnetted network share their 172.18.0.0/24 subnets and apply the /24 subnet mask of their receiving interface.

R2 summarizes 172.16.0.0/24 subnets as 172.16.0.0 because 172.17.1.0 is a different network (172.17.0.0 class B network).

R3 summarizes 172.18.0.0/24 subnets as 172.18.0.0 because 172.17.1.0 is a different network (172.17.0.0 class B network).

172.16.10.0/24

172.16.12.0/24

172.16.11.0/24

172.16.13.0/24

172.16.1.0/24

172.16.20.0/24 172.16.22.0/24

172.16.21.0/24 172.16.23.0/24

172.17.1.0/24

172.18.10.0/24

172.18.19.0/24

172.18.20.0/24

172.18.21.0/24

172.16.0.0172.18.0.0


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192.168.1.0/24 through 192.168.4.0/24 are individual Class C networks (not subnetted).

Routers with interfaces on these different networks share these individual non-subnetted networks and apply the default /24 Class C subnet mask of their receiving interface.

All routers receive the 192.168.1.0/24 through 192.168.4.0/24 as individual Class C networks.

R1 summarizes 172.16.0.0/24 subnets as 172.16.0.0 because 10.0.0.0 is a different network (10.0.0.0 is a class A network).

R3 summarizes 172.16.0.0/24 subnets as 172.16.0.0 because 172.17.1.0/24 is a different network (172.17.0.0 class B network.

R2 receives 172.16.0.0 from R1 and 172.16.0.0 from R3 and applies the default /16 Class B mask to both. R2 has two equal cost routes for the 172.16.0.0/16 network in its routing table.

172.16.10.0/24

172.16.12.0/24

172.16.11.0/24

172.16.13.0/24

10.0.0.0/30

192.168.1.0/24 192.168.3.0/24

192.168.2.0/24 192.168.4.0/24

172.17.1.0/24

172.16.100.0/24

172.16.101.0/24

172.16.102.0/24

172.16.102.0/24

172.16.0.0172.16.0.0

Anyone see a problem for R2 when it receives a packet for 172.16.x.x?


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Disadvantage of Automatic Summarization

Discontiguous network, two or more subnets separated by at least one other major network.

172.30.0.0/16 is a discontiguous network.

172.30.0.0/16 172.30.0.0/16

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Discontiguous Networks Do Not Converge with RIPv1R1(config)# router ripR1(config-router)# network 172.30.0.0R1(config-router)# network 209.165.200.0



RIPv1 configuration is correct, but it is unable to determine all the networks in this discontiguous topology.

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Discontiguous Networks Do Not Converge with RIPv1

What routing update will be sent by R1 and R3?

172.30.0.0 major network address, a summary route to R2.

172.30.0.0/16 172.30.0.0/16

172.30.0.0172.30.0.0

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Discontiguous Networks Do Not Converge with RIPv1R1# show ip route

172.30.0.0/24 is subnetted, 3 subnetsC 172.30.1.0 is directly connected, FastEthernet0/0C 172.30.2.0 is directly connected, FastEthernet0/1

R3# show ip route

172.30.0.0/24 is subnetted, 3 subnetsC 172.30.100.0 is directly connected, FastEthernet0/0C 172.30.200.0 is directly connected, FastEthernet0/1

What 172.30.0.0 networks/subnets do you expect to see in R1’s routing table?

What 172.30.0.0 networks/subnets do you expect to see in R3’s routing table?

Note: The book/curriculum mistakenly has the following routes for R1 and R3 (Book: Figure 5-15 and 5-17). These routes are NOT in the routing tables.

R1: R 172.30.0.0 [120/2] via 209.165.200.230, 00:00:26, Serial0/0/0R3: R 172.30.0.0 [120/2] via 209.165.200.233, 00:00:22, Serial0/0/1

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Discontiguous Networks Do Not Converge with RIPv1R2# show ip route

R 172.30.0.0/16 [120/1] via 209.165.200.234, 00:00:14, Serial0/0/1[120/1] via 209.165.200.229, 00:00:19, Serial0/0/0

R2 has two equal-cost paths to the 172.30.0.0 network.

What will R2 do when it receives traffic for a host on a 172.30.0.0 network ie. 172.30.200.10?

R2 will load-balance traffic destined for any subnet of 172.30.0.0.

This means that R1 will get half of the traffic and R3 will get the other half of the traffic, whether or not the destination of the traffic is for one of their LANs.

R2# show ip route


172.30.0.0/16 172.30.0.0/16

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Discontiguous Networks Do Not Converge with RIPv1

Classful routing protocols do not support discontiguous networks because they do not include the subnet mask in the routing update.

Classless routing protocols (RIPv2, EIGRP, OSPF, IS-IS, BGP) do support discontiguous networks.

R2# show ip route


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Default routes are used by routers to represent all routes that are not specifically in the routing table.

172.30.1.0/24

172.30.2.0/24

172.30.3.0/24

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In today’s networks, customers:

Do not necessarily have to exchange routing updates with their ISP.

Do not need a listing for every route on the Internet.

A Default Route sends all unmatched traffic to the ISP router.

ISP configures a static route pointing to the customer router for addresses inside the customer’s network.

Default Routes

ISP

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Configuration Changes for R2 and R3

R2(config)# router ripR2(config-router)# no network 192.168.4.0R2(config-router)# exitR2(config)# ip route 0.0.0.0 0.0.0.0 serial 0/0/1

R3(config)# no router ripR3(config)# ip route 172.30.0.0 255.255.252.0 serial 0/0/1

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Routing Table

R1 has all 172.30.0.0/24 subnets, but will drop packets for all other networks.

No default route (coming)


172.30.0.0/24 is subnetted, 3 subnetsC 172.30.1.0 is directly connected, FastEthernet0/0

C 172.30.2.0 is directly connected, Serial0/0/0R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:05, Serial0/0/0

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Routing Table

R2 has routes for 172.30.0.0/16 subnets.

R2 has static default route for all other networks

R2# show ip route<output omitted>Gateway of last resort is 0.0.0.0 to network 0.0.0.0

172.30.0.0/24 is subnetted, 3 subnetsR 172.30.1.0 [120/1] via 172.30.2.1, 00:00:03, Serial0/0/0

C 172.30.2.0 is directly connected, Serial0/0/0C 172.30.3.0 is directly connected, FastEthernet0/0

192.168.4.0/30 is subnetted, 1 subnets

C 192.168.4.8 is directly connected, Serial0/0/1S* 0.0.0.0/0 is directly connected, Serial0/0/1

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Routing Table

R3 has static route for 172.30.0.0/16 network.

Doesn’t matter if or how 172.30.0.0/16 is subnetted, R3 will forward packets to R2.


172.30.0.0/22 is subnetted, 1 subnetsS 172.30.0.0 is directly connected, Serial0/0/1


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You can configure static default route on every router but:

It is inefficient

It will not react to topology changes

In many routing protocols, including RIP, you can use the default- information originate command in router configuration mode to specify that this router is to originate default information, by propagating the static default route in RIP updates.


172.30.0.0/24 is subnetted, 3 subnetsC 172.30.1.0 is directly connected, FastEthernet0/0

C 172.30.2.0 is directly connected, Serial0/0/0R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:05, Serial0/0/0

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R2(config)# router ripR2(config-router)# default-information originateR2(config-router)# endR2# debug ip ripRIP: sending v1 update to 255.255.255.255 via Serial0/0/0

(172.30.2.2)RIP: build update entries

subnet 0.0.0.0 metric 1subnet 172.30.3.0 metric 1

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The static default route on R2 has been propagated to R1 in a RIP update.

R1 has connectivity to the LAN on R3 and any destination on the Internet.

R1# show ip route<output omitted>* - candidate default, U - per-user static route, o - ODR

Gateway of last resort is 172.30.2.2 to network 0.0.0.0172.30.0.0/24 is subnetted, 3 subnets

C 172.30.2.0 is directly connected, Serial0/0/0R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:16, Serial0/0/0C 172.30.1.0 is directly connected, FastEthernet0/0

R* 0.0.0.0/0 [120/1] via 172.30.2.2, 00:00:16, Serial0/0/0

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Topics




RIP Operation


RIPv1: Scenario A

Enable RIP: router rip Command

Specifying Networks


Verifying RIP: show ip route

Verifying RIP: show ip protocols

Verifying RIP: debug ip rip

Passive Interfaces





Sending RIP Updates

Advantages and Disadvantages of Automatic Summarization




ccna e2 05 ripv1

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