Chapter_5_RIP version 1

RIP version 1
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Routing Protocols and Concepts – Chapter 5
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.
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
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
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
RIPv1
Administrative Distance
RIP’s default administrative distance is 120
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)#
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
Verification and Troubleshooting
Show ip Route
To verify and troubleshoot routing
Use the following commands:
show ip route
show ip protocols
debug ip rip
Verification and Troubleshooting
show ip protocols command
Displays routing protocol configured on router
Verification and Troubleshooting
Debug ip rip command
Used to display RIP routing updates as they are happening
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
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 R1
S0/0/0 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
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
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
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
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
Summary: Commands used by RIP