Enabling RIP

Lesson Title, Size 30

2007 Cisco Systems, Inc. All rights reserved.

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What Is a Routing Protocol?

Routing protocols are used between routers to determine paths and maintain routing tables. After the path is determined, a router can route a routed protocol.

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Autonomous Systems: Interior or Exterior Routing Protocols

An autonomous system is a collection of networks under a common administrative domain. IGPs operate within an autonomous system. EGPs connect different autonomous systems.

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Classes of Routing Protocols

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Administrative Distance: Ranking Routes

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Distance VectorSources of Information and Discovering Routes

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

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Distance VectorSources of Information and Discovering Routes

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

Routing Table 10.1.0. 0 10.2.0. 0 E0 S0 0 0

Routing Table 10.2.0. 0 10.3.0. 0 S0 S1 0 0

Routing Table 10.3.0. 0 10.4.0. 0 S0 E0 0 0

Routers discover the best path to destinations from each neighbor

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Distance VectorSources of Information and Discovering Routes

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

Routing Table 10.1.0. 0 10.2.0. 0 10.3.0. 0 E0 S0 S0 0 0 1

Routing Table 10.2.0. 0 10.3.0. 0 10.4.0. 0 10.1.0. 0 S0 S1 S1 S0 0 0 1 1

Routing Table 10.3.0. 0 10.4.0. 0 10.2.0. 0 S0 E0 S0 0 0 1

Routers discover the best path to destinations from each neighbor

2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.05-8

Distance VectorSources of Information and Discovering Routes

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

Routing Table 10.1.0. 0 10.2.0. 0 10.3.0. 0 10.4.0. 0 E0 S0 S0 S0 0 0 1 2

Routing Table 10.2.0. 0 10.3.0. 0 10.4.0. 0 10.1.0. 0 S0 S1 S1 S0 0 0 1 1

Routing Table 10.3.0. 0 10.4.0. 0 10.2.0. 0 10.1.0. 0 S0 E0 S0 S0 0 0 1 2

Routers discover the best path to destinations from each neighbor

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ICND1 v1.05-9

Distance VectorMaintaining Routing Information

Process to update this routing table Topology change causes routing table update

Updates proceed step-by-step from router to router

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Distance VectorMaintaining Routing Information

Process to update this routing table Router A sends out this updated routing table after the next period expires Topology change causes routing table update

Updates proceed step-by-step from router to router

2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.05-11

Distance VectorMaintaining Routing Information

Process to update this routing table Router A sends out this updated routing table after the next period expires Process to update this routing table Topology change causes routing table update

Updates proceed step-by-step from router to router

2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.05-12

Maintaining Routing Information Problem Routing Loops

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

E0

Routing Table 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S0 0 0 1 2

Routing Table 10.2.0.0 10.3.0.0 10.4.0.0 10.1.0.0 S0 S1 S1 S0 0 0 1 1

Routing Table 10.3.0.0 10.4.0.0 10.2.0.0 10.1.0.0 S0 E0 S0 S0 0 0 1 2

Each node maintains the distance from itself to each possible destination network
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Maintaining Routing Information Problem Routing Loops

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

E0

Routing Table 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S0 0 0 1 2

Routing Table 10.2.0.0 10.3.0.0 10.4.0.0 10.1.0.0 S0 S1 S1 S0 0 0 1 1

Routing Table 10.3.0.0 10.4.0.0 10.2.0.0 10.1.0.0 S0 S0 S0 0 1 2 E0 Down

Slow convergence produces inconsistent routing

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Maintaining Routing Information Problem Routing Loops

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

Routing Table 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S0 0 0 1 2

Routing Table 10.2.0.0 10.3.0.0 10.4.0.0 10.1.0.0 S0 S1 S1 S1 0 0 1 1

Routing Table 10.3.0.0 10.4.0.0 10.2.0.0 10.1.0.0 S0 S0 S0 S0 0 2 1 2

Router C concludes that the best path to network 10.4.0.0 is through Router B
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Maintaining Routing Information Problem Routing Loops

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

E0

Routing Table 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S0 0 0 1 4

Routing Table 10.2.0.0 10.3.0.0 10.4.0.0 10.1.0.0 S0 S1 S1 S0 0 0 3 1

Routing Table 10.3.0.0 10.4.0.0 10.2.0.0 10.1.0.0 S0 S0 S0 S0 0 2 1 2

Router A updates its table to reflect the new but erroneous hop count
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Symptom: Counting to Infinity

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

Routing Table 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S0 0 0 1 6

Routing Table 10.2.0.0 10.3.0.0 10.4.0.0 10.1.0.0 S0 S1 S1 S0 0 0 5 1

Routing Table 10.3.0.0 10.4.0.0 10.2.0.0 10.1.0.0 S0 S0 S0 S0 0 4 1 2

Packets for network 10.4.0.0 bounce between routers A, B, and C Hop count for network 10.4.0.0 counts to infinity
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Solution: Defining a Maximum

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

Routing Table 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S0 0 0 1 16

Routing Table 10.2.0.0 10.3.0.0 10.4.0.0 10.1.0.0 S0 S1 S1 S0 0 0 16 1

Routing Table 10.3.0.0 S0 10.4.0.0 S0 10.2.0.0 S0 10.1.0.0 S0 0 16 1 2

Define a limit on the number of hops to prevent infinite loops

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Solution: Split Horizon

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

X
Routing Table 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S0 0 0 1 2 Routing Table 10.2.0.0 10.3.0.0 10.4.0.0 10.1.0.0 S0 S1 S1 E1 0 0 1 2

X
Routing Table 10.3.0.0 10.4.0.0 10.2.0.0 10.1.0.0 S0 S0 S0 S0 0 0 1 2

It is never useful to send information about a route back in the direction from which the original packet came

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Solution: Triggered Updates

Network 10.4.0.0 is unreachable

Network 10.4.0.0 is unreachable

Network 10.4.0.0 is unreachable

10.2.0.0
E0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

S0

S0

Router sends updates when a change in its routing table occurs

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Solution: Route Poisoning

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

Routing Table 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S0 0 0 1 2

Routing Table 10.2.0.0 10.3.0.0 10.4.0.0 10.1.0.0 S0 S1 S1 E1 0 0 1 2

Routing Table 10.3.0.0 S0 10.4.0.0 S0 10.2.0.0 S0 10.1.0.0 S0 0

Infinity

1 2

Routers set the distance of routes that have gone down to infinity

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Solution: Poison Reverse

10.1.0.0
E0

10.2.0.0 A
S0 S0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

Poison Reverse
Routing Table 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S0 0 0 1 2 Routing Table 10.2.0.0 10.3.0.0 10.4.0.0 10.1.0.0 S0 S1 S1 E1 0 0
Possi bly 2 Down

Routing Table 10.3.0.0 S0 10.4.0.0 S0 10.2.0.0 S0 10.1.0.0 S0 0

Infinity

1 2

Poison Reverse overrides split horizon

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Solution: Hold-Down Timers

Update after hold-down Time

Network 10.4.0.0 is unreachable

10.2.0.0
E0

10.3.0.0 B
S1 S0

10.4.0.0 C
E0

S0

S0

Update after hold-down Time

Network 10.4.0.0 is down then back up then back down

Router keeps an entry for the network possibly down state, allowing time for other routers to recompute for this topology change

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ICND1 v1.05-23

RIPv1 and RIPv2 Comparison

RIPv1 Routing protocol Supports variable-length subnet mask? Sends the subnet mask along with the routing update? Addressing type Defined in Supports manual route summarization? Authentication support? Classful No No Broadcast RFC 1058 No No

RIPv2 Classless Yes Yes Multicast RFCs 1721, 1722, and 2453 Yes Yes

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IP Routing Configuration Tasks

Router configuration Select routing protocols Specify networks or interfaces

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RIP Configuration
RouterX(config)

# router rip

Starts the RIP routing process

RouterX(config

router)#

version 2

Enables RIP version 2

RouterX(config-router)# network

network-number

Selects participating attached networks Requires a major classful network number

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RIP Configuration Example

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Verifying the RIP Configuration

Routing Protocol is "rip" Sending updates every 30 seconds, next due in 6 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: rip Default version control: send version 2, receive version 2 Interface Send Recv Triggered RIP Key-chain FastEthernet0/0 2 2 Serial0/0/2 2 2

Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 10.0.0.0 172.16.0.0 Routing Information Sources: Gateway Distance Last Update 10.1.1.2 120 00:00:25 Distance: (default is 120) RouterA#
2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.05-28

Displaying the IP Routing Table

RouterA# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route, o - ODR T - traffic engineered route Gateway of last resort is not set 172.16.0.0/24 is subnetted, 1 subnets 172.16.1.0 is directly connected, fastethernet0/0 10.0.0.0/24 is subnetted, 2 subnets 10.2.2.0 [120/1] via 10.1.1.2, 00:00:07, Serial0/0/2 10.1.1.0 is directly connected, Serial0/0/2 192.168.1.0/24 [120/2] via 10.1.1.2, 00:00:07, Serial0/0/2

C R C R

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ICND1 v1.05-29

debug ip rip Command

RouterA# debug ip rip RIP protocol debugging is on RouterA# 00:06:24: RIP: received v1 update from 10.1.1.2 on Serial0/0/2 00:06:24: 10.2.2.0 in 1 hops 00:06:24: 192.168.1.0 in 2 hops 00:06:33: RIP: sending v1 update to 255.255.255.255 via FastEthernet0/0 (172.16.1.1) 00:06:34: network 10.0.0.0, metric 1 00:06:34: network 192.168.1.0, metric 3 00:06:34: RIP: sending v1 update to 255.255.255.255 via Serial0/0/2 (10.1.1.1) 00:06:34: network 172.16.0.0, metric 1

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ICND1 v1.05-30

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ICND1 v1.05-31