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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: RIPv1 & RIPv2 – 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 • RIPv1 - a classful routing protocol • RIPv2 - a classless routing protocol © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 24 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 25 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 26 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 27 RIPv1 Administrative Distance – RIP’s default administrative distance is 120 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 28 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 29 Basic RIPv1 Configuration Router RIP Command – To enable RIP enter: • Router rip at the global configuration prompt • Prompt will look like R1(config-router)# © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 30 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 © 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 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 R1 • S0/0/0 and Fa0/0 on R2 © 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 RIPv1 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 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 43 Default Route and RIPv1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 44 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 © 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 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 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 47 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 48