Introduction to Local and Wide Area Networks

Transcription

1 Introduction to Local and Wide Area Networks Lecturers Amnach Khawne Jirasak Sittigorn Chapter 1 1

2 Routing Protocols and Concepts Chapter 4 : Distance Vector Routing Protocols Chapter 5 : RIP version 1 Chapter 1 2

3 Distance Vector Routing Protocols Routing Protocols and Concepts Chapter 4 Chapter 1 3

4 Objectives Identify the characteristics ti of distance vector routing protocols. Describe the network discovery process of distance vector routing protocols using Routing Information Protocol (RIP). Describe the processes to maintain accurate routing tables used by distance vector routing protocols. Identify the conditions leading to a routing loop and explain the implications for router performance. Recognize that distance vector routing protocols are in use today Chapter 1 4

5 Distance Vector Routing Protocols Examples of Distance Vector routing protocols: Routing Information Protocol (RIP) Interior Gateway Routing Protocol (IGRP) Enhanced Interior Gateway Routing Protocol (EIGRP) Chapter 1 5

6 Distance Vector Routing Protocols Distance Vector Technology The e 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 Chapter 1 6

7 Distance Vector Routing Protocols Characteristics of Distance Vector routing protocols: Periodic updates Neighbors Broadcast updates Entire routing table is included with routing update Chapter 1 7

8 Distance Vector Routing Protocols Routing Protocol Algorithm: -Defined as a procedure for accomplishing a certain task Chapter 1 8

9 Distance Vector Routing Protocols Routing Protocol Characteristics Criteria used to compare routing protocols includes Time to convergence Scalability Resource usage Implementation p & maintenance Chapter 1 9

10 Distance Vector Routing Protocols Chapter 1 10

11 Network Discovery Router initial start up (Cold Starts) -Initial network discovery Directly connected networks are initially placed in routing table Chapter 1 11

12 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 Chapter 1 12

13 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 Chapter 1 13

14 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 Chapter 1 14

15 Routing Table Maintenance Periodic Updates: RIPv1 & RIPv2 These are time intervals in which a router sends out its entire routing table. Chapter 1 15

16 Routing Table Maintenance RIP uses 4 timers -Update timer (default 30) -Invalid timer (default 180) -Holddown timer (default 180) -Flush timer (default 240) Chapter 1 16

17 Routing Table Maintenance Bounded Updates: EIGRP EIRPG routing updates are -Partial updates -Triggered by topology changes -Bounded d -Non periodic Chapter 1 17

18 Routing Table Maintenance Triggered Updates Conditions in which triggered updates are sent -Interface changes state -Route becomes unreachable -Route is placed in routing table Chapter 1 18

19 Routing Table Maintenance Random Jitter Synchronized updates A condition where multiple routers on multi access LAN segments transmit routing updates at the same time. Problems with synchronized updates -Bandwidth consumption -Packet collisions Solution to problems with synchronized updates - Used of random variable called RIP_JITTER Chapter 1 19

20 Routing Loops Routing loops are A condition in which a packet is continuously transmitted within a series of routers without ever reaching its destination. Chapter 1 20

21 Routing Loops Routing loops may be caused by: -Incorrectly configured static ti 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 Chapter 1 21

22 Routing Loops Count to Infinity This is a routing loop whereby packets bounce infinitely around a network. Chapter 1 22

23 Routing Loops Setting a maximum Distance Vector routing protocols set a specified metric value to indicate infinity Once a router counts to infinity it it marks the route as unreachable Chapter 1 23

24 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 p through network with the most current information. Chapter 1 24

25 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. Chapter 1 25

26 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 Chapter 1 26

27 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. Chapter 1 27

28 Routing Protocols Today Factors used to determine whether to use RIP or EIGRP include -Network size -Compatibility between models of routers -Administrative knowledge Chapter 1 28

29 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 Chapter 1 29

30 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 Chapter 1 30

31 Summary Characteristics of Distance Vector routing protocols Periodic updates RIP routing updates include the entire routing table Neighbors are defined as routers that share a link and are configured to use the same protocol The network discovery process for D.V. routing protocol Directly connected routes are placed in routing table 1 st If a routing protocol is configured then Routers will exchange routing information Convergence is reached when all network routers have the same network information Chapter 1 31

32 Summary DV D.V. routing protocols maintains i routing tables by RIP sending out periodic updates RIP using 4 different timers to ensure information is accurate and convergence is achieved in a timely manner EIGRP sending out triggered updates D.V. routing protocols may be prone to routing loops routing loops are a condition in which packets continuously traverse a network Mechanisms used to minimize routing loops include defining maximum hop count, holddown timers, split horizon, route poisoning and triggered updates Chapter 1 32

33 Summary Conditions that can lead to routing loops include Incorrectly configured static routes Incorrectly configured route redistribution ib ti Slow convergence Incorrectly configured discard routes How routing loops can impact network performance includes: Excess use of bandwidth CPU resources may be strained Network convergence is degraded Routing updates may be lost or not processed Chapter 1 33

34 Summary Routing Information Protocol (RIP) A distance vector protocol that has 2 versions RIPv1 a classful routing protocol RIPv2 - a classless routing protocol Enhanced Interior Gateway Routing Protocol (EIGRP) A distance vector routing protocols that has some features of link state routing protocols A Cisco proprietary routing protocol Chapter 1 34

35 RIP version 1 Routing Protocols and Concepts Chapter 5 Chapter 1 35

36 Objectives Describe the functions, characteristics, ti 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 Chapter 1 36

37 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 Chapter 1 37

38 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 Chapter 1 38

39 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 Chapter 1 39

40 RIPv1 IP addresses initially iti divided id d into classes -Class A -Class B -Class C RIP is a classful routing protocol -Does not send subnet masks in routing updates Chapter 1 40

41 RIPv1 Administrative Distance RIP s default administrative distance is 120 Chapter 1 41

42 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 Chapter 1 42

43 Basic RIPv1 Configuration Router RIP Command To enable RIP enter: -Router rip at the global configuration prompt -Prompt will look like R1(config-router)# Chapter 1 43

44 Basic RIPv1 Configuration Specifying i 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 Chapter 1 44

45 Verification and Troubleshooting Show ip Route To verify and troubleshoot routing -Use the following commands: -show ip route -show ip pprotocols -debug ip rip Chapter 1 45

46 Verification and Troubleshooting show ip protocols command -Displays routing protocol configured on router Chapter 1 46

47 Verification and Troubleshooting Debug ip rip command -Used to display RIP routing updates as they are happening Chapter 1 47

48 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 Chapter 1 48

49 Verification and Troubleshooting Passive interfaces Chapter 1 49

50 Automatic ti Summarization Modified Topology The original scenario has been modified such that: Three classful l networks are used: / / /24 The /16 0 0/16 network is subnetted into three subnets: / / /24 The following devices are part of the /16 classful network address: All interfaces on R1 S0/0/0 and Fa0/0 on R2 Chapter 1 50

51 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 Chapter 1 51

52 Automatic ti Summarization Boundary Routers RIP automatically summarizes classful networks Boundary routers summarize RIP subnets from one major network to another. Chapter 1 52

53 Automatic ti 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. Chapter 1 53

54 Automatic Summarization Sending RIP Updates RIP uses automatic summarization to reduce the size of a routing table. Chapter 1 54

55 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. Chapter 1 55

56 Automatic ti Summarization Disadvantage of Automatic Summarization: -Does not support discontiguous networks Chapter 1 56

57 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. Chapter 1 57

58 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 s0/0/1 Chapter 1 58

59 Default Route and RIPv1 Router R1 Router R2 Router R3 Chapter 1 59

60 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. Chapter 1 60

61 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 Chapter 1 61

62 Summary: Commands used by RIP Rtr(config)#router rip Command Command s purpose Enables RIP routing process Rtr(config-router)#network Associates a network with a RIP routing gprocess Rtr#debug ip rip used to view real time RIP routing updates Rtr(config-router)#passive-interface fa0/0 Rtr(config-router)#default-information originate Rtr#show ip protocols Prevent RIP updates from going out an interface Used by RIP to propagate default routes Used to display timers used by RIP Chapter 1 62