chapter 5 rip version 1 cis 82 routing protocols and concepts rick graziani cabrillo college...

Chapter 5RIP version 1

CIS 82 Routing Protocols and Concepts

Rick Graziani

Cabrillo College

graziani@cabrillo.edu

Last Updated: 3/10/2009

Note This presentation will be updated prior to March. 25, 2008 The audio of the lecture for this presentation will be available on

my web site after March. 25, 2008

My web site is www.cabrillo.edu/~rgraziani. For access to these PowerPoint presentations and other

materials, please email me at graziani@cabrillo.edu.

For further information This presentation is an

overview of what is covered in the curriculum/book.

For further explanation and details, please read the chapter/curriculum.

Book: Routing Protocols

and Concepts By Rick Graziani and

Allan Johnson ISBN: 1-58713-206-0 ISBN-13: 978-58713-

Topics RIPv1: 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: debu ip rip Passive Interfaces

Automatic Summarization Modified Topology B Boundary Routers and

Automatic Summarization Processing RIP Updates Sending RIP Updates Advantages and

Disadvantages of Automatic Summarization

Default Route and RIPv1 Modified Topology C Propagating the Default Route

in RIPv1

Download Packet Tracer Topology: cis82-RIPv1-A-student.pkt

RIPv1: A Distance Vector, Classful Routing Protocol

Background and Perspective RIPv1 Characteristics and Message Format RIP Operation

RIPv1: Distance Vector, Classful Routing Protocol

Why learn RIP? Still in use today. Help understand fundamental concepts and comparisons of

protocols Classful (RIPv1) vs classless (RIPv2)

Background and Perspective

RIP is not a protocol “on the way out.” In fact, an IPv6 form of RIP called RIPng (next generation) is now

available..

Background and Perspective

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

RIPv1 Characteristics and Message Format

RIP characteristics: Distance Vector or Link State?

Distance vector routing protocol. Metric?

Hop count Maximum Hop count?

Greater than 15 are considered unreachable. Routing table updates are broadcasted every…?

30 seconds. (RIPv2 uses multicasts)

RIPv1 Characteristics and Message Format

IP Address Classes and Classful Routing

RIPv1: Classful routing protocol. Does not send subnet mask in update.

No subnet mask

IP Address Classes and Classful Routing

R2 receives an RIP update with a network address. R2 adds the network address and mask to the routing table. A router either uses the subnet mask: (discussed later)

Local interface or Default classful subnet mask

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

RIP Update network-add

Routing Table

Network-add/mask

Basic RIPv1 Configuration

RIPv1 Scenario A Enable RIP: router rip Command Specifying Networks

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

Enabling RIP: router rip Command

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

R1# conf t

Enter 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 networks

mobile Mobile routes

odr On Demand stub Routes

ospf Open Shortest Path First (OSPF)

rip Routing Information Protocol (RIP)

R1(config)# router rip

R1(config-router)#

Enabling RIP: router rip Command

no router rip To remove the RIP routing process from a device Stops the RIP process Erases all existing RIP configuration commands.

R1# conf t

R1(config-router)# network 192.168.1.0

R1(config-router)# exit

R1(config)# no router rip

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

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).

Specifying Networks

RIP Update

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.

Only directly connected classful network addresses!

Administrative Distance

What is the administrative distance of a network route learned via RIP? 120

R3# show ip route

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

* - candidate default, U - per-user static route, o - ODR

P - 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, Serial0/0/1

R 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, Serial0/0/1

C 192.168.5.0/24 is directly connected, FastEthernet0/0

R = RIP

Administrative Distance

Where is the administrative distance displayed using this command?

R3# show ip protocols

Routing Protocol is “rip”

Routing Information Sources:

Gateway Distance Last Update

192.168.6.2 120 00:00:10

Distance: (default is 120)

Verification and Troubleshooting

Verifying RIP: show ip route Verifying RIP: show ip protocols Verifying RIP: debu ip rip Passive Interfaces

Verifying RIP: show ip route on all three routers…

R1# show ip route

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

R 192.168.4.0/24 [120/1] via 192.168.2.2, 00:00:02, Serial0/0/0

R 192.168.5.0/24 [120/2] via 192.168.2.2, 00:00:02, Serial0/0/0

R 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.

Verifying RIP: show ip route Command

R2# show ip route

R 192.168.5.0/24 [120/1] via 192.168.4.1, 00:00:12, Serial0/0/1

R 192.168.1.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0

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

R3# show ip route

R 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, Serial0/0/1

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

R1# show ip route

R 192.168.5.0/24 [120/2] via 192.168.2.2, 00:00:23, Serial0/0/0

Examine and discuss the show ip protocols Command

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.

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.

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

Filtering and redistribution are both CCNP-level topics.

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

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.

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)

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.

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.

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

Split horizon rule. R1 is will not advertise networks back to R2 that were learned

from R2.

RIP: received v1 update from 192.168.2.1 on Serial0/0/0

192.168.1.0 in 1 hops

192.168.5.0 in 1 hops

RIP: sending v1 update to 255.255.255.255 via FastEthernet0/0

(192.168.3.1)

RIP: build update entries

network 192.168.1.0 metric 2

Directly Connected

Learned via RIP from R1

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

(192.168.4.2)

Directly Connected

RIP: sending v1 update to 255.255.255.255 via Serial0/0/0

(192.168.2.2)

Directly Connected

R2# undebug all

All possible debugging has been turned off

Does R2 need to send RIP updates out Fa 0/0? What are the disadvantages to this?

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?

Passive Interfaces

What about using on R2:

R2(Config-router)# no network 192.168.3.0 R2 would not advertise this LAN as a route in updates sent to R1

and R3. Correct solution is to use the passive-interface command

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

Passive Interfaces – Use it on R2…

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

Passive InterfacesR2# show ip protocols

Interface Send Recv Triggered RIP Key-chain

Serial0/0/0 1 1 2

Serial0/0/1 1 1 2

Automatic network summarization is in effect

Routing for Networks:

192.168.2.0

192.168.3.0

192.168.4.0

Passive Interface(s):

FastEthernet0/0

Routing Information Sources:

Gateway Distance Last Update

192.168.2.1 120 00:00:27

192.168.4.1 120 00:00:23

Distance: (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

Automatic Summarization

Modified Topology B Boundary Routers and Automatic Summarization Processing RIP Updates Sending RIP Updates Advantages and Disadvantages of Automatic Summarization

Modified Topology: Scenario B

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

Modified Topology: Scenario B

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

Configuration Changes for R1

R1(config)# interface fa0/0

R1(config-if)# ip address 172.30.1.1 255.255.255.0

R1(config-if)# interface S0/0/0

R1(config-if)# no router rip

R1(config-router)# end

R1# show run

router rip

passive-interface FastEthernet0/0

network 172.30.0.0

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.

Configuration Changes for R2R2(config)# interface S0/0/0

R2(config-if)# interface fa0/0

R2# show run

router rip

network 172.30.0.0

network 192.168.4.0

! <output omitted>

IOS automatically corrects subnet entries to classful network address

Configuration Changes for R3

R3(config)# interface fa0/0

R3# show run

router rip

network 192.168.4.0

network 192.168.5.0

Boundary Routers and Automatic Summarization

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

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.

Processing RIP Updates

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 route

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

C 172.30.2.0 is directly connected, Serial0/0/0

C 172.30.3.0 is directly connected, FastEthernet0/0

R 192.168.5.0/24 [120/1] via 192.168.4.10, 00:00:16, Serial0/0/1

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 Mask

Same Classful Major Network Use mask of interface

Different Classful Major Network Use default classful mask

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)

172.30.1.0 in 1 hops

R2# show ip route (selected output)

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

R2# debug ip rip

RIP protocol debugging is on

RIP: sending v1 update to 255.255.255.255 via Serial0/0/0 (172.30.2.2)

Sending RIP Updates

192.168.4.0/24

192.168.5.0/24

Sending RIP Updates

172.30.3.0

192.168.4.0

192.168.5.0 172.30.0.0

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

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

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).

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

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

Discontiguous Networks Do Not Converge with RIPv1

R1(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.

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

172.30.0.0

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, Serial0/0/0

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

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

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

Default Route and RIPv1

Modified Topology C Propagating the Default Route in RIPv1

Modified Topology: Scenario C

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

Default Routes

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.

Default route that sends all traffic to the ISP router. ISP configures a static route pointing to the customer router for

addresses inside the customer’s network.

Configuration Changes for R2 and R3

R2(config-router)# no network 192.168.4.0

R2(config-router)# exit

R2(config)# ip route 0.0.0.0 0.0.0.0 serial 0/0/1

R3(config)# no router rip

R3(config)# ip route 172.30.0.0 255.255.252.0 serial 0/0/1

Routing Table

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

No default route (coming)

R1# show ip route

R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:05, Serial0/0/0

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

Gateway of last resort is 0.0.0.0 to network 0.0.0.0

R 172.30.1.0 [120/1] via 172.30.2.1, 00:00:03, Serial0/0/0

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

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.

R3# show ip route

S 172.30.0.0 is directly connected, Serial0/0/1

Propagating the Default Route in RIPv1

Can configure static default route on every router but: inefficient does 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.

R1# show ip route

R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:05, Serial0/0/0

R2(config-router)# default-information originate

R2# debug ip rip

subnet 0.0.0.0 metric 1

subnet 172.30.3.0 metric 1

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

* - candidate default, U - per-user static route, o - ODR

Gateway of last resort is 172.30.2.2 to network 0.0.0.0

R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:16, Serial0/0/0

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

Topics RIPv1: 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: debu ip rip Passive Interfaces

Automatic Summarization Modified Topology B Boundary Routers and

Automatic Summarization Processing RIP Updates Sending RIP Updates Advantages and

Disadvantages of Automatic Summarization

Default Route and RIPv1 Modified Topology C Propagating the Default Route

in RIPv1

Chapter 5RIP version 1

CIS 82 Routing Protocols and Concepts

Rick Graziani

Cabrillo College

graziani@cabrillo.edu

Last Updated: 3/10/2009

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