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
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.
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.
21. 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.
24. 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. 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.
29. 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.
30. 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) 1986-1999 by cisco Systems, Inc.
Compiled Mon 08-Feb-99 18:18 by phanguye
Image text-base: 0x03050C84, data-base: 0x00001000
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. 33
show running-config and
show startup-config Commands
wg_ro_c#show startup-config
Using 1359 out of 32762 bytes
!
version 12.0
!
-- More --
wg_ro_c#show running-config
Building configuration...
Current configuration:
!
version 12.0
!
-- More --
In NVRAMIn RAM
• Displays the current and saved configuration
33. 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. 36
Configuring a Router’s 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. 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
38. 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
39. 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.
40. 41
Passwords
There are five passwords for Router
Privileged Mode Password – 2
Line Console Password
Auxiliary Port Password
Telnet Password
45. 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. 48
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
48. 49
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
49. 50
LAB – Interface Configuration
S0 S0E0
10.0.0.1
10.0.0.2
30.0.0.220.0.0.1
20.0.0.2 30.0.0.1
A
S0
E0
40.0.0.2
40.0.0.1
B
S1
50. 51
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
51. 52
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 10.0.0.1 255.0.0.0
R1(config-if)#no shutdown
R1(config-if)#exit
R1(config)#interface serial 0
R1(config-if)#ip address 20.0.0.1 255.255.255.0
R1(config-if)# bandwidth 64
R1(config-if)#clock rate 64000 (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 = serial e = Ethernet f = fast Ethernet
56. 57
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
57. 58
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
59. 60
To route, a router needs to know:
Destination addresses
Sources it can learn from
Possible routes
Best route
What is Routing?
172.16.1.010.120.2.0
60. 61
What is Routing? (cont.)
Networ
k
Protoco
l
Destinatio
n
Network
Connected
Learned
10.120.2.0
172.16.1.0
Exit
Interface
E0
S0
Routed Protocol: IP
Routers must learn destinations that are not
directly connected
172.16.1.010.120.2.0
E0
S0
61. 62
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.
62. 63
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 B’s IP address.
E0 E1
10.0.0.1
10.0.0.2
A B 20.0.0.2
20.0.0.1
63. 65
LAB – Interface Configuration
S0 S0E0
10.0.0.1
10.0.0.2
30.0.0.220.0.0.1
20.0.0.2 30.0.0.1
A
S0
E0
40.0.0.2
40.0.0.1
B
S1
64. 66
Test The Connection
• Host A can ping router R1 and R2
• To enable Host A to Ping Host B we need to configure
Routes
66. 68
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
68. 70
ip route The command used to create the static route.
destination_network The network you’re 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 that’s on a directly
connected network.
exitinterface You can use it in place of the next-hop address if you want, but it’s
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 can’t 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 30.0.0.0 255.0.0.0 20.0.0.2
70. 72
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.
71. 73
S0 S0E0
10.0.0.1
10.0.0.2
30.0.0.220.0.0.1
20.0.0.2 30.0.0.1
A
S0
E0
40.0.0.2
40.0.0.1
B
S1
R1# config t
R1(config)#no ip route 30.0.0.0 255.0.0.0 20.0.0.2
R1(config)#no ip route 40.0.0.0 255.0.0.0 20.0.0.2
R2# config t
R2(config)#no ip route 10.0.0.0 255.0.0.0 20.0.0.1
R2(config)#no ip route 40.0.0.0 255.0.0.0 30.0.0.2
R3# config t
R3(config)#no ip route 10.0.0.0 255.0.0.0 30.0.0.1
R3(config)#no ip route 20.0.0.0 255.0.0.0 30.0.0.1
Removing IP Route
72. 74
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
S0E0
E010.0.0.1
10.0.0.2 40.0.0.2
20.0.0.1
20.0.0.2
30.0.0.1
A B
S0
S1
30.0.0.2
40.0.0.1
73. 75
Stub Network
ip route 0.0.0.0 0.0.0.0 172.16.2.2
Default Routes
172.16.2.1
SO
172.16.1.0
B
172.16.2.2
Network
A B
This route allows the stub network to reach all known
networks beyond router A.
10.0.0.0
74. 76
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 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]
This is sometimes referred to as a “Quad-Zero” route.
Example using next hop address:
Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.4.1
Example using the exit interface:
Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0
76. 78
Default Route LAB
Configuration
S0
S0E0
E0
10.0.0.1
10.0.0.2 40.0.0.2
20.0.0.1
20.0.0.2
30.0.0.1
A B
S0
S1
30.0.0.2
40.0.0.1
R1# config t
R1(config)#ip route 0.0.0.0 0.0.0.0 20.0.0.2
R3# config t
R3(config)#ip route 0.0.0.0 0.0.0.0 30.0.0.1
R2# config t
R2(config)#ip route 10.0.0.0 255.0.0.0 20.0.0.1
R2(config)#ip route 40.0.0.0 255.0.0.0 30.0.0.2
77. 79
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.
Networ
k
Protoco
l
Destinatio
n
Network
Connected
RIP
IGRP
10.120.2.0
172.16.2.0
172.17.3.0
Exit
Interface
E0
S0
S1
Routed Protocol: IP
Routing protocol: RIP, IGRP
172.17.3.0
172.16.1.010.120.2.0
E0
S0
78. 80
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
79. 81
IGP
Interior Gateway Protocol
(IGP)
Exterior Gateway
Protocol (EGP)
EGP
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
80. 82
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
82. 84
Distance Vector
RIP V1
IGRP
RIP V2
Link state
OSPF
Hybrid
EIGRP
Types or Classes of Routing
Protocols
83. 85
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
84. 86
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
85. 87
• Routers pass periodic copies of routing table to neighbor
routers and accumulate distance vectors.
Distance Vector Routing
Protocols
86. 88
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?
192.168.10.1
192.168.20.1
87. 89
Distance Vector
There are two Distance Vector Protocol, Both uses different metric
RIP – Hops
IGRP - Composite
192.168.10.1
192.168.20.1
88. 90
Distance Vector
DV protocol are known as Routing by rumor
RIP uses only Hop count
RI routing table metric for 192.168.20.1 network will be
3
2
192.168.10.1
192.168.20.1
0
1
1
2
2
3R1
89. 91
Distance Vector
192.168.10.1
192.168.20.1
56 kbps
1 Mbps
1 Mbps
1 Mbps
56 kbps
• IGGRP uses bandwidth and delay as Metric
• RI routing table metric for 192.168.20.1 network will be
– 30
– 60
R1
10
10
10
30 30
192.168.10.1
94. 96
• Router C concludes that the best path to network
10.4.0.0 is through router B.
Inconsistent Routing Entries
(Cont.)
95. 97
• Router A updates its table to reflect the new but
erroneous hop count.
Inconsistent Routing Entries
(Cont.)
96. 98
Hop count for network 10.4.0.0 counts to infinity.
Count to Infinity
97. 99
• Packets for network 10.4.0.0 bounce (loop) between
routers B and C.
Routing Loops
98. 100
• Define a limit on the number of hops to prevent
infinite loops.
Defining a Maximum
99. 101
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
100. 102
• It is never useful to send information about a route back
in the direction from which the original information
came.
Split Horizon
101. 103
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
10.4.0.0 in its update to Router C.
102. 104
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 10.4.0.0 was
unavailable it would have immediately poisoned the
route to that network by setting its hop count to the
routing protocol’s infinity value
• In the case of RIP, that would mean a hop count of 16.
103. 105
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.
105. 107
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
108. 110
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).
109. 111
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 it’s 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.
110. 112
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 172.16.0.0
The network numbers are based on the network class
addresses, not subnet addresses or individual host addresses.
111. 113
RIP Configuration
S0
S0
E0
E0
192.168.10.1
A B
S0
S1
R1# config t
R1(config)# )#router rip
R1(config)#network 192.168.10.0
R1(config)#network 192.168.20.0
R2# config t
R2(config)#router rip
R2(config)#network 192.168.20.0
R2(config)#network 192.168.30.0192.168.10.2
192.168.20.1
192.168.20.2
192.168.30.1
192.168.30.2 192.168.40.1
192.168.40.2
R3# config t
R3(config)# )#router rip
R3(config)#network 192.168.30.0
R3(config)#network 192.168.40.0
115. 117
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 192.168.10.0
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.
116. 118
RIP Version 2 (RIPv2)
R1# config t
R1(config)# )#router rip
R1(config)#network 192.168.10.0
R1(config)#network 192.168.20.0
R1(config)#version 2
117. 119
Exercise - RIP Version 2
Configuration
S0
S0
E0
E0
192.168.0.16/29
A B
S0
S1
192.168.0.4/30 192.168.0.8/30
192.168.0.32/28
1. Find out the IP Address and SNM of each interfaces
123. 125
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. 130
Verifying the IGRP Routing
Tables
LabA#sh ip route
[output cut]
I 192.168.50.0 [100/170420] via 192.168.20.2, Serial0/0
I 192.168.40.0 [100/160260] via 192.168.20.2, Serial0/0
I 192.168.30.0 [100/158360] via 192.168.20.2, Serial0/0
C 192.168.20.0 is directly connected Serial0/0
C 192.168.10.0 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
128. 131
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
