Cisco IOS (originally Internetwork 1
operating system. 2
is a family of software used on most Cisco Systems routers and current Cisco network switches.(Earlier switches ran CatOS.) 3
IOS is a package of routing, switching, internetworking and telecommunications functions integrated 4
into multitasking operating system. 5
And let's take a look to the IOS features. 6
Cisco IOS is located in flash 7
Can be updated Copied to valotile RAM Provides software – hardware communication 8
The Cisco IOS command-line interface (CLI) is the primary user interface used for configuring, monitoring, 9
and maintaining Cisco devices. CLI can be accessed using ; 10
Console Telnet SSH AUX 11
Every Cisco router or a switch has a console port (also known 12
as the management port) on its back side. 13
As in here Console port is used to connect a computer directly to a router or switch and manage 14
the router or switch since there is no display 15
device for 16
or switch . Normally router 17
Console port 18
is a RJ45 port. A special type of cable, 19
known as roll over cable is used to connect the Serial/COM port of the computer to the router 20
or switch console port. One end of the cable is RJ49 type and a DB9 to RJ45 21
converter is molded on the other end. 22
And let's go with the telnet, an access method to CLI. 23
Telnet is a protocol that allows you to connect to remote devices over a network. Using telnet 24
client software on your computer, 25
you can make a connection to a remote device. In most cases, 26
you'll need to log into the remote host, which requires that you have an account on that system. By default, 27
telnet does not encrypt any data sent over the connection including passwords. Because of serious security 28
concerns. 29
it is recommended to use SSH instead of Telnet.SSH, also known as Secure Shell, is a network 30
that provides administrators with a secure way to access a remote networking device. Secure 31
Shell provides strong authentication and secure encrypted data communication between two network 32
devices 33
Because of that it is always preferred over Telnet. 34
Terminal emulation programs are Used for accessing to a device using console port, telnet or SSH. 35
Popular programs are ; Putty Secure CRT Hyper Terminal 36
Here is Putty window, if you want to for example communicate to a device you enter 37
the host name or the IP address of the device and you choose the connection type in here whether its 38
Telnet, SSH ,serial etc. 39
Then you click the open and communicate with device. 40
IOS has four different mod guys and they are ; User EXEC Privileged Global Configuration specific configuration 41
User EXEC Mode is the first mode a user has access to 42
after logging into the router. The user mode can be identified by the > 43
prompt following the router name. 44
This mode allows the user to execute only the basic commands, such as those that show the system's status. 45
Privileged mode mode allows users to view the system configuration, restart 46
the system, and enter router configuration mode. Privileged mode 47
also allows all the commands 48
that are available in user mode 49
Global Configuration mode mode allows users to modify the running system configuration 50
this mod has various submodes, starting with global configuration mode, and they are known as specific 51
configuration modes.If you want to navigate between defferent IOS modes 52
We have some options, for example if you're in the user exec mode and want to navigate to 53
privilege exec mode we're using the Enable command. 54
If you're in the Enable mode and if you want to switch to the config mod we're using the conf t 55
configure terminal command and we're in the global config 56
And if you want to switch to your specific interface configuration mode for example you type interface 57
and the interfaces name on the config mode basically and you get into the config interface mode. Note : 58
exit command is used for passing to the upper mode always. 59
So let's take a look to the IOS features . IOS provides context sensitive help. 60
Please keep in mind that question mark is your best friend always. 61
All right let's take a look to the screen and let's say that we are trying to type clock set command 62
instead of typing clock 63
If I type for example C L O and k Ios is warning us and saying ask that this is an unknown command 64
for example. for example if you could not remember the commands clock 65
But if you just remind CL if you type C L and put a question mark IOS shows you the commands 66
that you can use in that IOS mode. for example if you type clock the command is right now. 67
it is OK. 68
And if you just hit the enter it again warns you that that is an incomplete command because we're 69
going to use the clock set as you know for example after cloak and you type. 70
The question mark and hit enter it's showing us that what commands more we can use after that command 71
for example it's offering us the set command and giving us some clues what the command is doing rightly. 72
And it's saying that set the time and they for example. 73
So let's go ahead with the context sensitive help 74
And for example we type clock set 75
And the clock for example, then if we had the question mark again, it's also saying us that we can use the 76
day of the month or we can type month. 77
keyword, All right clock set 78
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And we have some shortcuts and hotkeys that we can use in IOS. 84
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If you want to encrypt all your passwords in your show run output we have a great command. we can use 125
service password encryption. 126
This command to encrypt all passwords on the show run out for example in here. 127
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