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1. 2 Cisco IOS Cisco technology is built around the Cisco Internetwork Operating System (IOS), which is the software that controls the routing and switching.

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Presentation on theme: "1. 2 Cisco IOS Cisco technology is built around the Cisco Internetwork Operating System (IOS), which is the software that controls the routing and switching."— Presentation transcript:

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2 2 Cisco IOS Cisco technology is built around the Cisco Internetwork Operating System (IOS), which is the software that controls the routing and switching functions of internetworking devices. A solid understanding of the IOS is essential for a network administrator.

3 3 The Purpose of Cisco IOS As with a computer, a router or switch cannot function without an operating system. Cisco calls its operating system the Cisco Internetwork Operating System or Cisco IOS.

4 4 Introduction to Routers A router is a special type of computer. It has the same basic components as a standard desktop PC. However, routers are designed to perform some very specific functions. Just as computers need operating systems to run software applications, routers need the Internetwork Operating System software (IOS) to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. The many parts of a router are shown below:

5 5 Router Memory Components ROM - Read Only Memory – Bootstrap/POST FLASH Memory - IOS Images are kept here - Erasable reprogrammable ROM - Contents are kept on Power down or reload RAM - Random Access memory - Routing Tables - Running Configuration - Contents are lost on reboot NVRAM- Start up configuration - Configuration Register - Contents are kept on reload

6 6 ROM Read-Only Memory ROM has the following characteristics and functions: Maintains instructions for power-on self test (POST) diagnostics Stores bootstrap program and basic operating system software Mini IOS

7 7 RAM Random Access Memory, also called dynamic RAM (DRAM) RAM has the following characteristics and functions: Stores routing tables Holds ARP cache Performs packet buffering (shared RAM) Provides temporary memory for the configuration file of the router while the router is powered on Loses content when router is powered down or restarted

8 8 NVRAM Non-Volatile RAM NVRAM has the following characteristics and functions: Provides storage for the startup configuration file Retains content when router is powered down or restarted Configuration Register – 16 bit register which decides boot sequence

9 9 Flash Flash memory has the following characteristics and functions: Holds the operating system image (IOS) Allows software to be updated without removing and replacing chips on the processor Retains content when router is powered down or restarted Can store multiple versions of IOS software Is a type of electronically erasable, programmable ROM (EEPROM)

10 10 Interfaces Interfaces have the following characteristics and functions: Connect router to network for frame entry and exit Can be on the motherboard or on a separate module Types of interfaces: Ethernet Fast Ethernet Serial ISDN BRI Loopback Console Aux

11 11 Router Internal Components

12 12 Router Power-On/Bootup Sequence 1.Perform power-on self test (POST). 2.Load and run bootstrap code. 3.Find the Cisco IOS software. 4.Load the Cisco IOS software. 5.Find the configuration. 6.Load the configuration. 7.Run the configured Cisco IOS software.

13 13 Boot Sequence ROMMonitor RXBoot FLASH Configuration Register C-FileNVRAM Y N Running Setup Mode Checks All interfaces RAM ROMMonitor RxBoot Flash

14 14 After the Post… After the POST, the following events occur as the router initializes: Step 1 The generic bootstrap loader in ROM executes. A bootstrap is a simple set of instructions that tests hardware and initializes the IOS for operation. Step 2 The IOS can be found in several places. The boot field of the configuration register determines the location to be used in loading the IOS. Step 3 The operating system image is loaded. Step 4 The configuration file saved in NVRAM is loaded into main memory and executed one line at a time. The configuration commands start routing processes, supply addresses for interfaces, and define other operating characteristics of the router. Step 5 If no valid configuration file exists in NVRAM, the operating system searches for an available TFTP server. If no TFTP server is found, the setup dialog is initiated.

15 15 Loading the Cisco IOS Software From Flash Memory The flash memory file is decompressed into RAM.

16 16 Loading the Configuration Load and execute the configuration from NVRAM. If no configuration is present in NVRAM, enter setup mode.

17 17 External Components of a 2600 Router

18 18 Internal Components of a 2600 Router

19 19 Computer/Terminal Console Connection

20 20 Modem Connection to Console/Aux Port

21 21 HyperTerminal Session Properties

22 22 Establishing a HyperTerminal Session Take the following steps to connect a terminal to the console port on the router: First, connect the terminal using the RJ-45 to RJ-45 rollover cable and an RJ-45 to DB-9 or RJ-45 to DB-25 adapter. Then, configure the terminal or PC terminal emulation software for 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow control.

23 23 Router Command Line Interface

24 24 IOS File System Overview

25 25 Router LED Indicators Cisco routers use LED indicators to provide status information. Depending upon the Cisco router model, the LED indicators will vary. An interface LED indicates the activity of the corresponding interface. If an LED is off when the interface is active and the interface is correctly connected, a problem may be indicated. If an interface is extremely busy, its LED will always be on. The green OK LED to the right of the AUX port will be on after the system initializes correctly.

26 26

27 27 Router User Interface Modes The Cisco command-line interface (CLI) uses a hierarchical structure. This structure requires entry into different modes to accomplish particular tasks. Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode. As a security feature the Cisco IOS software separates sessions into two access levels, user EXEC mode and privileged EXEC mode. The privileged EXEC mode is also known as enable mode.

28 28 Overview of Router Modes

29 29 Router Modes

30 30 CLI Command Modes All command-line interface (CLI) configuration changes to a Cisco router are made from the global configuration mode. Other more specific modes are entered depending upon the configuration change that is required. Global configuration mode commands are used in a router to apply configuration statements that affect the system as a whole. The following command moves the router into global configuration mode Router#configure terminal (or config t) Router(config)# When specific configuration modes are entered, the router prompt changes to indicate the current configuration mode. Typing exit from one of these specific configuration modes will return the router to global configuration mode. Pressing Ctrl-Z returns the router to all the way back privileged EXEC mode.

31 31 Show Version Command wg_ro_a#show version Cisco Internetwork Operating System Software IOS (tm) 2500 Software (C2500-JS-L), Version 12.0(3), RELEASE SOFTWARE (fc1) Copyright (c) by cisco Systems, Inc. Compiled Mon 08-Feb-99 18:18 by phanguye Image text-base: 0x03050C84, data-base: 0x ROM: System Bootstrap, Version 11.0(10c), SOFTWARE BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c), RELEASE SOFTWARE(fc1) wg_ro_a uptime is 20 minutes System restarted by reload System image file is "flash:c2500-js-l_120-3.bin" (output omitted) --More-- Configuration register is 0x2102

32 32 Viewing the Configuration

33 33 show running-config and show startup-config Commands wg_ro_c#show startup-config Using 1359 out of bytes ! version 12.0 ! -- More -- wg_ro_c#show running-config Building configuration... Current configuration: ! version 12.0 ! -- More -- In NVRAM In RAM Displays the current and saved configuration

34 34 Configurations in two locations - RAM and NVRAM. The running configuration is stored in RAM. Any configuration changes to the router are made to the running-configuration and take effect immediately after the command is entered. The startup-configuration is saved in NVRAM and is loaded into the router's running-configuration when the router boots up. To save the running-configuration to the startup configuration, type the following from privileged EXEC mode (i.e. at the "Router#" prompt.) Router# copy run start Saving Configurations

35 35 Command Abbreviation Show Configuration – sh conf Configure Terminal – conf t Line auxillary – line aux Line console – line con

36 36 Configuring a Routers Name A router should be given a unique name as one of the first configuration tasks. This task is accomplished in global configuration mode using the following commands: Router(config)#hostname Gates Gates(config)# As soon as the Enter key is pressed, the prompt changes from the default host name (Router) to the newly configured host name (which is Gates in the example above).

37 37 Setting the Clock with Help

38 38 Message Of The Day (MOTD) A message-of-the-day (MOTD) banner can be displayed on all connected terminals. Enter global configuration mode by using the command config t Enter the command banner motd # Welcome to Gates Training #. Save changes by issuing the command copy run start

39 39 Privileged Mode Command # show startup-config # show running-config # show version # show flash # show interfaces # show interfaces s 0 # show history # show terminal # terminal history size 25

40 40 Password Passwords restrict access to routers. Passwords should always be configured for virtual terminal lines and the console line. Passwords are also used to control access to privileged EXEC mode so that only authorized users may make changes to the configuration file.

41 41 Passwords There are five passwords for Router Privileged Mode Password – 2 Line Console Password Auxiliary Port Password Telnet Password

42 42 Privileged Mode Password Gates(config)# enable password gates Encrypted privilege mode password Gates(config)# enable secret gates1

43 43 Line Password Gates(config)# line console 0 Gates(config)# password cisco Gates(config)# login

44 44 Aux Port Password Gates(config)# line aux 0 Gates(config)# password cisco Gates(config)# login

45 45 Connecting to Aux Port

46 46 Configuring a Telnet Password A password must be set on one or more of the virtual terminal (VTY) lines for users to gain remote access to the router using Telnet. Typically Cisco routers support five VTY lines numbered 0 through 4.

47 47 Telnet Password Gates(config)# line vty 0 4 Gates(config)# password cisco Gates(config)# login

48 48

49 49 Encrypting Passwords Only the enable secret password is encrypted by default Need to manually configure the user-mode and enable passwords for encryption To manually encrypt your passwords, use the service password-encryption command Router#config t Enter configuration commands, one per line. End with CNTL/Z. Router(config)#service password-encryption

50 50 Disable Passwords Gates(config)# no enable password Gates(config)# no enable secret For the Console Gates(config)# line con 0 Gates(config)# no password Gates(config)# line vty 0 4 Gates(config)# no password

51 51 LAB – Interface Configuration S0 E A S0 E B S1

52 52 Descriptions Setting descriptions on an interface is helpful to the administrator Only locally significant R1(config)#int e0 R1(config-if)#description Sales Lan R1(config-if)#int s0 R1(config-if)#desc Wan to Mumbai

53 53 Configuring Interfaces An interface needs an IP Address and a Subnet Mask to be configured. All interfaces are shutdown by default. The DCE end of a serial interface needs a clock rate. R1#config t R1(config)#int e0 R1(config)#Description Connoted to Host R1(config-if)#ip address R1(config-if)#no shutdown R1(config-if)#exit R1(config)#interface serial 0 R1(config-if)#ip address R1(config-if)# bandwidth 64 R1(config-if)#clock rate (required for serial DCE only) R1(config-if)#no shutdown R1(config-if)#exit R1(config)#exit R1# On new routers, Serial 1 would be just Serial 0/ 1 and e0 would be f0/0. s = seriale = Ethernetf = fast Ethernet

54 54 DCE DTE To find out DCE or DTE #Show controllers s 0

55 55 Viewing Configuration To Check the status of interface #Show IP interface brief or #Sh IP int brief

56 56 Saving and Erasing Configurations To copy RAM to NVRAM # copy run startup-config To remove all configuration # erase startup-config # reload

57 57

58 58 Objectives Upon completion of this chapter, you will be able to complete the following tasks: Distinguish the use and operation of static and dynamic routes Configure and verify a static route Identify how distance vector IP routing protocols such as RIP and IGRP operate on Cisco routers Enable Routing Information Protocol (RIP) Enable Interior Gateway Routing Protocol (IGRP) Verify IP routing with show and debug commands

59 59 Routing The process of transferring data from one local area network to another Layer 3 devices Routed protocol Enables to forward packet from one router to another – Ex – IP, IPX Routing protocol sends and receives routing information packets to and from other routers – Ex - RIP, OSPF, IGRP Routing protocols gather and share the routing information used to maintain and update routing tables. That routing information is in turn used to route a routed protocol to its final destination

60 60 Routing From Raj House #213, 4 th Street Jayanagar, Bangalore To Ram House #452, 2 nd Street Dadar, Mumbai

61 61 To route, a router needs to know: Destination addresses Sources it can learn from Possible routes Best route What is Routing?

62 62 What is Routing? (cont.) Network Protocol Destination Network Connected Learned Exit Interface E0 S0 Routed Protocol: IP Routers must learn destinations that are not directly connected E0 S0

63 63 Route Types Static routing - network administrator configures information about remote networks manually. They are used to reduce overhead and for security. Dynamic routing - information is learned from other routers, and routing protocols adjust routes automatically. Because of the extra administrative requirements, static routing does not have the scalability of dynamic routing.

64 64 IP Routing Process Step-by-step what happens when Host A wants to communicate with Host B on a different network A user on Host A pings Host Bs IP address. E0E A B

65 65 LAB Configuration S0 E AB

66 66 LAB – Interface Configuration S0 E A S0 E B S1

67 67 Test The Connection Host A can ping router R1 and R2 To enable Host A to Ping Host B we need to configure Routes

68 68 IP Routing The different types of routing are: Static routing Default routing Dynamic routing

69 69 Static Routes Benefits No overhead on the router CPU No bandwidth usage between routers Adds security Disadvantage Administrator must really understand the internetwork If a network is added to the internetwork, the administrator has to add a route to it on all routers Not feasible in large networks

70 70 –R1(config)# iproute DestAddress SNM Nexthop address R1(config)#ip route network [mask] {address | interface}[distance] [permanent] Static Route Configuration

71 71 ip route The command used to create the static route. destination_network The network youre placing in the routing table. mask The subnet mask being used on the network. next-hop_address The address of the next-hop router that will receive the packet and forward it to the remote network. This is a router interface thats on a directly connected network. exitinterface You can use it in place of the next-hop address if you want, but its got to be on a point-to-point link, such as a WAN administrative_distance By default, static routes have an administrative distance of 1 (or even 0 if you use an exit interface instead of a next-hop address) permanent If the interface is shut down, or the router cant communicate to the next-hop router, the route will automatically be discarded from the routing table. Choosing the permanent option keeps the entry in the routing table no matter what happens. ip route [destination_network] [mask] [next-hop_address or exitinterface] [administrative_distance] [permanent Static Route Configuration R1(config)#ip route

72 72 LAB – Static Route Configuration S0 E A S0 E B S1 R1# config t R1(config)#ip route R1(config)#ip route R2# config t R2(config)#ip route R2(config)#ip route R3# config t R3(config)#ip route R3(config)#ip route

73 73 Verifying Static Route Configuration After static routes are configured it is important to verify that they are present in the routing table and that routing is working as expected. The command show running-config is used to view the active configuration in RAM to verify that the static route was entered correctly. The show ip route command is used to make sure that the static route is present in the routing table.

74 74 S0 E A S0 E B S1 R1# config t R1(config)#no ip route R1(config)#no ip route R2# config t R2(config)#no ip route R2(config)#no ip route R3# config t R3(config)#no ip route R3(config)#no ip route Removing IP Route

75 75 Default Routes Can only use default routing on stub networks Stub networks are those with only one exit path out of the network The only routers that are considered to be in a stub network are R1 and R3 S0 E A B S0 S

76 76 Stub Network ip route Default Routes SO B Network A B This route allows the stub network to reach all known networks beyond router A

77 77 Configuring Default Routes Default routes are used to route packets with destinations that do not match any of the other routes in the routing table. A default route is actually a special static route that uses this format: ip route [next-hop-address | outgoing interface] This is sometimes referred to as a Quad-Zero route. Example using next hop address: Router(config)#ip route Example using the exit interface: Router(config)#ip route s0/0

78 78 S0 E A B S0 S LAB Configuration

79 79 Default Route LAB Configuration S0 E A B S0 S R1# config t R1(config)#ip route R3# config t R3(config)#ip route R2# config t R2(config)#ip route R2(config)#ip route

80 80 What is a Routing Protocol? Routing protocols are used between routers to determine paths and maintain routing tables. Once the path is determined a router can route a routed protocol. Network Protocol Destination Network Connected RIP IGRP Exit Interface E0 S0 S1 Routed Protocol: IP Routing protocol: RIP, IGRP E0 S0

81 81 Autonomous System AS 2000 AS 3000 IGP Interior Gateway Protocols are used for routing decisions within an Autonomous System. Exterior Gateway Protocols are used for routing between Autonomous Systems EGP AS 1000 An Autonomous System (AS) is a group of IP networks, which has a single and clearly defined routing policy. Group of routers which can exchange updates AS are identified by numbers Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67) All Routing protocols are categorized as IGP or EGP Routing Categories

82 82 IGP Interior Gateway Protocol (IGP) Exterior Gateway Protocol (EGP) EGP Interior Gateway Protocol (IGP) AS 1000 AS 2000 AS 3000 Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67) Routing Categories

83 83 An autonomous system is a collection of networks under a common administrative domain. IGPs operate within an autonomous system. EGPs connect different autonomous systems. Autonomous Systems: Interior or Exterior Routing Protocols

84 84 Types or Classes of Routing Protocols

85 85 Distance Vector RIP V1 IGRP RIP V2 Link state OSPF Hybrid EIGRP Types or Classes of Routing Protocols

86 86 Classful Routing Overview Classful routing protocols do not include the subnet mask with the route advertisement. Within the same network, consistency of the subnet masks is assumed. Summary routes are exchanged between foreign networks. Examples of classful routing protocols: RIP Version 1 (RIPv1) IGRP

87 87 Classless Routing Overview Classless routing protocols include the subnet mask with the route advertisement. Classless routing protocols support variable-length subnet masking (VLSM) and subnetting Examples of classless routing protocols: RIP Version 2 (RIPv2) EIGRP OSPF IS-IS

88 88 Routers pass periodic copies of routing table to neighbor routers and accumulate distance vectors. Distance Vector Routing Protocols

89 89 Distance Vector Uses Bellman Ford Algorithm It needs to find out the shortest path from one network to other How to determine which path is best?

90 90 Distance Vector There are two Distance Vector Protocol, Both uses different metric RIP – Hops IGRP - Composite

91 91 Distance Vector DV protocol are known as Routing by rumor RIP uses only Hop count RI routing table metric for network will be R1

92 92 Distance Vector kbps 1 Mbps 56 kbps IGGRP uses bandwidth and delay as Metric RI routing table metric for network will be –30 –60 R

93 93 Routing Loops A network problem in which packets continue to be routed in an endless circle

94 94 Routers discover the best path to destinations from each neighbor. Sources of Information and Discovering Routes

95 95 Each node maintains the distance from itself to each possible destination network. Inconsistent Routing Entries

96 96 Slow convergence produces inconsistent routing. Inconsistent Routing Entries (Cont.)

97 97 Router C concludes that the best path to network is through router B. Inconsistent Routing Entries (Cont.)

98 98 Router A updates its table to reflect the new but erroneous hop count. Inconsistent Routing Entries (Cont.)

99 99 Hop count for network counts to infinity. Count to Infinity

100 100 Packets for network bounce (loop) between routers B and C. Routing Loops

101 101 Define a limit on the number of hops to prevent infinite loops. Defining a Maximum

102 102 Maximum Hop Count One way of solving routing loop problem is to define a maximum hop count. RIP permits a hop count of up to 15, so anything that requires 16 hops is deemed unreachable The maximum hop count will control how long it takes for a routing table entry to become invalid

103 103 It is never useful to send information about a route back in the direction from which the original information came. Split Horizon

104 104 Split Horizon Solution to the Routing Loop problem Split Horizon is a rule that routing information cannot be sent back in the direction from which it was received Had split horizon been used in our example, Router B would not have included information about network in its update to Router C.

105 105 Route Poisoning Route Poisoning. Usually used in conjunction with split horizon Route poisoning involves explicitly poisoning a routing table entry for an unreachable network Once Router C learned that network was unavailable it would have immediately poisoned the route to that network by setting its hop count to the routing protocols infinity value In the case of RIP, that would mean a hop count of 16.

106 106 Triggered Updates New routing tables are sent to neighboring routers on a regular basis. RIP updates occur every 30 seconds However a triggered update is sent immediately in response to some change in the routing table. The router that detects a topology change immediately sends an update message to adjacent routers that, in turn, generate triggered updates notifying their adjacent neighbors of the change. Triggered updates, used in conjunction with route poisoning, ensure that all routers know of failed routes.

107 107 Triggered Updates Graphic

108 108 Holddowns Holddowns are a technique used to ensure that a route recently removed or changed is not reinstated by a routing table update from another route Holddown prevents regular update messages from reinstating a route that is going up and down (called flapping) Holddowns prevent routes from changing too rapidly by allowing time for either the downed route to come back up Holddowns make a router wait a period of time before accepting an update for a network whose status or metric has recently changed

109 109 Solution: Holddown Timers

110 110 Pinhole Congestion Mbps 56kbps

111 111 RIP Timers Route update timer Sets the interval (typically 30 seconds) between periodic routing updates Route invalid timer Determines the length of time (180 seconds) before a router determines that a route has become invalid Holddown timer This sets the amount of time during which routing information is suppressed. This continues until either an update packet is received with a better metric or until the holddown timer expires. The default is 180 seconds Route flush timer Sets the time between a route becoming invalid and its removal from the routing table (240 seconds).

112 112 Routing Information Protocol (RIP) Routing Information Protocol (RIP) is a true distance-vector routing protocol. It sends the complete routing table out to all active interfaces every 30 seconds RIP only uses hop count to determine the best way to a remote network It has a maximum allowable hop count of 15 AD is 120 Bellman-ford algorithm Works well in small networks, but its inefficient on large networks RIP version 1 uses only classful routing, which means that all devices in the network must use the same subnet mask RIP version 2 does send subnet mask information with the route updates. This is called classless routing.

113 113 Router Configuration The router command starts a routing process. The network command is required because it enables the routing process to determine which interfaces participate in the sending and receiving of routing updates. An example of a routing configuration is: Gates(config)#router rip Gates(config-router)#network The network numbers are based on the network class addresses, not subnet addresses or individual host addresses.

114 114 RIP Configuration S0 E A B S0 S1 R1# config t R1(config)# )#router rip R1(config)#network R1(config)#network R2# config t R2(config)#router rip R2(config)#network R2(config)#network R3# config t R3(config)# )#router rip R3(config)#network R3(config)#network

115 115 Verifying RIP Configuration

116 116 Displaying the IP Routing Table

117 117 debug ip rip Command

118 118 Passive Interface Passive-interface command prevents RIP update broadcasts from being sent out a defined interface, but same interface can still receive RIP updates R1#config t R1(config)#router rip R1(config-router)#network R1(config-router)#passive-interface serial 0 Passive-interface command depends upon the routing protocol RIP router with a passive interface will still learn about the networks advertised by other routers EIGRP, a passive-interface will neither send nor receive updates.

119 119 RIP Version 2 (RIPv2) R1# config t R1(config)# )#router rip R1(config)#network R1(config)#network R1(config)#version 2

120 120 Exercise - RIP Version 2 Configuration S0 E /29 A B S0 S / / /28 1.Find out the IP Address and SNM of each interfaces

121 121 Exercise - RIP Version 2 Configuration S0 E A B S0 S

122 122 Exercise - RIP Version 2 Configuration S0 E /29 A B S0 S / / /28 R2# config t R2(config)#router rip R2(config)#network R2(config)#network R2(config)#version 2 R1# config t R1(config)# )#router rip R1(config)#network R1(config)#network R1(config)#version 2 R3# config t R3(config)# )#router rip R3(config)#network R3(config)#network R3(config)#version 2

123 123 © 2002, Cisco Systems, Inc. All rights reserved. 123 Enabling IGRP

124 124 CISCO Proprietary More scalable than RIP Sophisticated metric Introducing IGRP

125 125 Bandwidth Delay Reliability Load MTU IGRP Composite Metric

126 126 IGRP Some of the IGRP key design characteristics emphasize the following: It is a distance vector routing protocol. Routing updates are broadcast every 90 seconds. Bandwidth, load, delay and reliability are used to create a composite metric. The main difference between RIP and IGRP configuration is that when you configure IGRP, you supply the autonomous system number. All routers must use the same number in order to share routing table information.

127 127 IGRP Vs RIP

128 128 IGRP Timers Update timers these specify how frequently routing-update messages should be sent. The default is 90 seconds. Invalid timers These specify how long a router should wait before declaring a route invalid if it doesnt receive a specific update about it. The default is 3*90 = 270. Holddown timers These specify the holddown period. The default is three times the update timer period plus 10 seconds. 280 seconds Flush timers These indicate how much time should pass before a route should be flushed from the routing table. The default is seven times the routing update period. If the update timer is 90 seconds by default, then 7 × 90 = 630 seconds elapse before a route will be flushed from the route table.

129 129 Configuring IGRP

130 130 IGRP Configuration S0 E A B S0 S1 R1# config t R1(config)# )#router igrp 10 R1(config)#network R1(config)#network R2# config t R2(config)#router igrp 10 R2(config)#network R2(config)#network R3# config t R3(config)# )#router igrp 10 R3(config)#network R3(config)#network

131 131 Verifying the IGRP Routing Tables LabA#sh ip route [output cut] I [100/170420] via , Serial0/0 I [100/160260] via , Serial0/0 I [100/158360] via , Serial0/0 C is directly connected Serial0/0 C is directly connected, FastEthernet0/0 The I means IGRP-injected routes. The 100 in [100/160360] is the administrative distance of IGRP. The 160,360 is the composite metric. The lower the composite metric, the better the route. To delete all routes clear ip route

132 132 Debug Commands debug ip igrp events Command summary of the IGRP routing information that is running on the network. debug ip igrp transactions Command shows message requests from neighbor routers asking for an update and the broadcasts sent from your router toward that neighbor router. no debug all – to turn off all debug

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