Distance Vector Routing Protocols and RIP V 1

Distance Vector Routing Protocols and RIP V. 1 Routing Protocols and Concepts – Chapter 4, 5 Editted by Nugroho Agus H. , M. Si. Version 4. 0 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1

Routing Protocol Algorithm: © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 2

Routing Protocol Characteristics – Criteria used to compare routing protocols includes • Time to convergence • Scalability • Resource usage • Implementation & maintenance © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 3

Network Discovery § Router initial start up (Cold Starts) – Initial network discovery • Directly connected networks are initially placed in routing table © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 4

Network Discovery § Initial Exchange of Routing Information – If a routing protocol is configured then: • Routers will exchange routing information • Routing updates received from other routers § Router checks update for new information – If there is new information: • Metric is updated • New information is stored in routing table © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 5

Network Discovery § Exchange of Routing Information – Router convergence is reached when • All routing tables in the network contain the same network information – Routers continue to exchange routing information • If no new information is found then Convergence is reached © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 6

Network Discovery § Convergence must be reached before a network is considered completely operable § Speed of achieving convergence consists of 2 interdependent categories – Speed of broadcasting routing information – Speed of calculating routes © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 7

Distance Vector Technology § - The Meaning of Distance Vector – A router using distance vector routing protocols knows 2 things: • Distance to final destination • Vector, or direction, traffic should be directed © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 8

Characteristics of Distance Vector routing protocols: – Periodic updates – Neighbors – Broadcast updates – Entire routing table is included with routing update © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 9

Examples of Distance Vector routing protocols: – Routing Information Protocol (RIP) – Interior Gateway Routing Protocol (IGRP) – Enhanced Interior Gateway Routing Protocol (EIGRP) © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 10

Distance Vector Routing Protocols © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 11

Routing Table Maintenance § Periodic Updates: RIPv 1 & RIPv 2 – These are time intervals in which a router sends out its entire routing table § RIP uses 4 timers – Update timer – Invalid timer – Holddown timer – Flush timer © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 12

Routing Loops § Routing loops are – A condition in which a packet is continuously transmitted within a series of routers without ever reaching its destination. © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 13

Routing Loops § Routing loops may be caused by: – – Incorrectly configured static routes Incorrectly configured route redistribution Slow convergence Incorrectly configured discard routes § Routing loops can create the following issues: – – Excess use of bandwidth CPU resources may be strained Network convergence is degraded Routing updates may be lost or not processed in a timely manner © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 14

Routing Loops § Count to Infinity – This is a routing loop whereby packets bounce infinitely around a network © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 15

Routing Loops § Setting a maximum § Distance Vector routing protocols set a specified metric value to indicate infinity – Once a router “counts to infinity” it marks the route as unreachable © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 16

Routing Loops § Preventing loops with holddown timers – Holddown timers allow a router to not accept any changes to a route for a specified period of time – Point of using holddown timers • Allows routing updates to propagate through network with the most current information © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 17

Routing Loops § The Split Horizon Rule is used to prevent routing loops § Split Horizon rule: – A router should not advertise a network through the interface from which the update came © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 18

Routing Loops § Split horizon with poison reverse – The rule states that once a router learns of an unreachable route through an interface, advertise it as unreachable back through the same interface © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 19

Routing Loops § IP & TTL – Purpose of the TTL field • The TTL field is found in an IP header and is used to prevent packets from endlessly traveling on a network § How the TTL field works – TTL field contains a numeric value • The numeric value is decreased by one by every router on the route to the destination • If numeric value reaches 0 then Packet is discarded © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 20

Routing Protocols Today § Factors used to determine whether to use RIP or EIGRP include – Network size – Compatibility between models of routers – Administrative knowledge © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 21

Routing Protocols Today § RIP – Features of RIP: • Supports split horizon & split horizon with poison reverse • Capable of load balancing • Easy to configure • Works in a multi vendor router environment © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 22

Routing Protocols Today § EIGRP – Features of EIGRP: • Triggered updates • EIGRP hello protocol used to establish neighbor adjacencies • Supports VLSM & route summarization • Use of topology table to maintain all routes • Classless distance vector routing protocol • Cisco proprietary protocol © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 23

§ Routing Information Protocol (RIP) – A distance vector protocol that has 2 versions • RIPv 1 - a classful routing protocol • RIPv 2 - a classless routing protocol © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 24

RIPv 1 § 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 25

RIPv 1 § 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 26

RIPv 1 § 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 27

RIPv 1 § Administrative Distance – RIP’s default administrative distance is 120 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 28

Basic RIPv 1 Configuration § A typical topology suitable for use by RIPv 1 includes: – Three router set up – No PCs attached to LANs – Use of 5 different IP subnets © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 29

Basic RIPv 1 Configuration § Router RIP Command – To enable RIP enter: • Router rip at the global configuration prompt • Prompt will look like R 1(config-router)# © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 30

Basic RIPv 1 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 31

Verification and Troubleshooting § Show ip Route § To verify and troubleshoot routing – Use the following commands: • show ip route • show ip protocols • debug ip rip © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 32

Verification and Troubleshooting § show ip protocols command – Displays routing protocol configured on router © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 33

Verification and Troubleshooting § Debug ip rip command – Used to display RIP routing updates as they are happening © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 34

Verification and Troubleshooting § Passive interface command – Used to prevent a router from sending updates through an interface – Example: • Router(config-router)#passive-interface-type interface-number © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 35

Passive interfaces © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 36

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 R 1 • S 0/0/0 and Fa 0/0 on R 2 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 37

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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 38

Boundary Routers – RIP automatically summarizes classful networks – Boundary routers summarize RIP subnets from one major network to another © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 39

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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 40

Automatic Summarization § Disadvantage of Automatic Summarization: – Does not support discontiguous networks © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 41

Automatic Summarization § Discontiguous Topologies do not converge with RIPv 1 § A router will only advertise major network addresses out interfaces that do not belong to the advertised route © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 42

Default Route and RIPv 1 § 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 s 0/0/1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 43

Default Route and RIPv 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 44

Default Route and RIPv 1 § Propagating the Default Route in RIPv 1 § 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 45

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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 46

Summary: Commands used by RIP 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 fa 0/0 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 47

© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 48