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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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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.
3
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-
206-3
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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
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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
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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)
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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..
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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
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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)
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RIPv1 Characteristics and Message Format
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RIPv1 Characteristics and Message Format
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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 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
/16
?
Basic RIPv1 Configuration
RIPv1 Scenario A Enable RIP: router rip Command Specifying Networks
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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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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)#
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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 rip
R1(config-router)# network 192.168.1.0
R1(config-router)# network 192.168.2.0
R1(config-router)# exit
R1(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 rip
R1(config-router)# network 192.168.1.0
R1(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.
R1(config)# router rip
R1(config-router)# network 192.168.1.0
R1(config-router)# network 192.168.2.0
R2(config)# router rip
R2(config-router)# network 192.168.2.0
R2(config-router)# network 192.168.3.0
R2(config-router)# network 192.168.4.0
R3(config)# router rip
R3(config-router)# network 192.168.4.0
R3(config-router)# network 192.168.5.0
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 route
Codes: C - connected, S - static, I - IGRP, R - RIP,
<some output omitted>
* - 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
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 00:00:10
Distance: (default is 120)
Verification and Troubleshooting
Verifying RIP: show ip route Verifying RIP: show ip protocols Verifying RIP: debu ip rip Passive Interfaces
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Verifying RIP: show ip route on all three routers…
R1# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,
<output omitted>
Gateway of last resort is not set
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
C 192.168.1.0/24 is directly connected, FastEthernet0/0
C 192.168.2.0/24 is directly connected, 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.
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Verifying RIP: show ip route Command
R2# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,
<output omitted>
Gateway of last resort is not set
C 192.168.4.0/24 is directly connected, Serial0/0/1
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
C 192.168.2.0/24 is directly connected, Serial0/0/0
C 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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Verifying RIP: show ip route Command
R3# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,
<output omitted>
Gateway of last resort is not set
C 192.168.4.0/24 is directly connected, Serial0/0/1
C 192.168.5.0/24 is directly connected, FastEthernet0/0
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
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Verifying RIP: show ip route Command
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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Verifying RIP: show ip protocols Command
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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Verifying RIP: show ip protocols Command
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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Verifying RIP: show ip protocols Command
Information about which RIP version is currently configured and which interfaces are participating in RIP updates.
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Verifying RIP: show ip protocols Command
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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Verifying RIP: show ip protocols Command
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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Verifying RIP: show ip protocols Command
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 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
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RIP: received v1 update from 192.168.4.1 on Serial0/0/1
192.168.5.0 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 entries
network 192.168.1.0 metric 2
network 192.168.2.0 metric 1
network 192.168.4.0 metric 1
network 192.168.5.0 metric 2
Directly Connected
Learned via RIP from R1
Learned via RIP from R3
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RIP: sending v1 update to 255.255.255.255 via Serial0/0/1
(192.168.4.2)
RIP: build update entries
network 192.168.1.0 metric 2
network 192.168.2.0 metric 1
network 192.168.3.0 metric 1
Directly Connected
Learned via RIP from R1
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RIP: sending v1 update to 255.255.255.255 via Serial0/0/0
(192.168.2.2)
RIP: build update entries
network 192.168.3.0 metric 1
network 192.168.4.0 metric 1
network 192.168.5.0 metric 2
Directly Connected
Learned via RIP from R3
R2# undebug all
All possible debugging has been turned off
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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?
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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
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Passive Interfaces – Use it on R2…
R2(config)# router rip
R2(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 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
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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
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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
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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)# ip address 172.30.2.1 255.255.255.0
R1(config-if)# no router rip
R1(config)# router rip
R1(config-router)# network 172.30.1.0
R1(config-router)# network 172.30.2.0
R1(config-router)# passive-interface FastEthernet 0/0
R1(config-router)# end
R1# show run
<output omitted>
!
router rip
passive-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 S0/0/0
R2(config-if)# ip address 172.30.2.2 255.255.255.0
R2(config-if)# interface fa0/0
R2(config-if)# ip address 172.30.3.1 255.255.255.0
R2(config-if)# interface S0/0/1
R2(config-if)# ip address 192.168.4.9 255.255.255.252
R2(config-if)# no router rip
R2(config)# router rip
R2(config-router)# network 172.30.0.0
R2(config-router)# network 192.168.4.8
R2(config-router)# passive-interface FastEthernet 0/0
R2(config-router)# end
R2# show run
<output omitted>
!
router rip
passive-interface FastEthernet0/0
network 172.30.0.0
network 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 fa0/0
R3(config-if)# ip address 192.168.5.1 255.255.255.0
R3(config-if)# interface S0/0/1
R3(config-if)# ip address 192.168.4.10 255.255.255.252
R3(config-if)# no router rip
R3(config)# router rip
R3(config-router)# network 192.168.4.0
R3(config-router)# network 192.168.5.0
R3(config-router)# passive-interface FastEthernet 0/0
R3(config-router)# end
R3# show run
<output omitted>
!
router rip
passive-interface FastEthernet0/0
network 192.168.4.0
network 192.168.5.0
!
<output omitted>
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Boundary Routers and Automatic Summarization
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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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
192.168.4.0/30 is subnetted, 1 subnets
C 192.168.4.8 is directly connected, Serial0/0/1
R 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 Mask
Same Classful Major Network Use mask of interface
Different 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 rip
RIP protocol debugging is on
RIP: 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 1
network 192.168.4.0 metric 1
network 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 Updates
172.30.3.0
192.168.4.0
192.168.5.0 172.30.0.0
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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).
64
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
65
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
66
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
R2(config)# router ripR2(config-router)# network 10.0.0.0R2(config-router)# network 209.165.200.0
R3(config)# router ripR3(config-router)# network 172.30.0.0R3(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
172.30.0.0
172.30.0.0
68
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
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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
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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
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
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
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
Default Route and RIPv1
Modified Topology C Propagating the Default Route in RIPv1
73
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
74
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.
75
Configuration Changes for R2 and R3
R2(config)# router rip
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
76
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
<output omitted>
Gateway of last resort is not set
172.30.0.0/24 is subnetted, 3 subnets
C 172.30.1.0 is directly connected, FastEthernet0/0
C 172.30.2.0 is directly connected, Serial0/0/0
R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:05, Serial0/0/0
77
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 subnets
R 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, Serial0/0/0
C 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, Serial0/0/1
S* 0.0.0.0/0 is directly connected, Serial0/0/1
78
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
<output omitted>
Gateway of last resort is not set
172.30.0.0/22 is subnetted, 1 subnets
S 172.30.0.0 is directly connected, Serial0/0/1
192.168.4.0/30 is subnetted, 1 subnets
C 192.168.4.8 is directly connected, Serial0/0/1
C 192.168.5.0/24 is directly connected, FastEthernet0/0
79
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
<output omitted>
Gateway of last resort is not set
172.30.0.0/24 is subnetted, 3 subnets
C 172.30.1.0 is directly connected, FastEthernet0/0
C 172.30.2.0 is directly connected, Serial0/0/0
R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:05, Serial0/0/0
80
Propagating the Default Route in RIPv1
R2(config)# router rip
R2(config-router)# default-information originate
R2(config-router)# end
R2# debug ip rip
RIP: 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 1
subnet 172.30.3.0 metric 1
81
Propagating the Default Route in RIPv1
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 0.0.0.0
172.30.0.0/24 is subnetted, 3 subnets
C 172.30.2.0 is directly connected, Serial0/0/0
R 172.30.3.0 [120/1] via 172.30.2.2, 00:00:16, Serial0/0/0
C 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
82
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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