© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
ITE PC v4.0
Chapter 1 1
RIP version 1
Routing Protocols and
Concepts – Chapter 5
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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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Chapter 1 3© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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
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Chapter 1 4© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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
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Chapter 1 5© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 6© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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RIPv1
 Administrative Distance
–RIP’s default administrative distance is 120
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Chapter 1 8© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 9© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 10© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Basic RIPv1 Configuration
 Specifying Networks
–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
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Chapter 1 11© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 12© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verification and Troubleshooting
 show ip
protocols
command
-Displays
routing
protocol
configured
on router
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Chapter 1 13© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verification and Troubleshooting
 Debug ip rip command
-Used to display RIP routing updates as they are
happening
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Chapter 1 14© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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
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Chapter 1 15© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Verification and Troubleshooting
 Passive interfaces
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Chapter 1 16© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 17© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 18© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Automatic Summarization
 Boundary Routers
–RIP automatically summarizes classful networks
–Boundary routers summarize RIP subnets from one
major network to another.
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Chapter 1 19© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Automatic Summarization
Processing 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.
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Chapter 1 20© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Automatic Summarization
 Sending RIP Updates
–RIP uses automatic summarization to reduce the
size of a routing table.
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Chapter 1 21© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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.
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Automatic Summarization
 Disadvantage of Automatic Summarization:
-Does not support discontiguous networks
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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.
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Chapter 1 24© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 25© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
Default Route and RIPv1
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Chapter 1 26© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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.
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Chapter 1 27© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 28© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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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Chapter 1 29© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public