Nov 18, 2011

Abstract of CCNA study guide-12 -Cisco IOS Basic configurations 1

Continue the series of  Abstract CCNA study guide book .
The IOS User Interface
The Cisco Internetwork Operating System (IOS) is the kernel of Cisco routers and most switches.
Cisco Router IOS
These are some important things that the Cisco router IOS software is responsible for:
-        Carrying network protocols and functions
-        Connecting high-speed traffic between devices
-        Adding security to control access and stop unauthorized network use
-        Providing scalability for ease of network growth and redundancy
-        Supplying network reliability for connecting to network resources

Connecting to a Cisco Router
There are different ways to Connect to Router:
the first is the console port. The Console port is usually an RJ-45 (8-pin modular) connection located at the back of the router—by default, there’s May or may not be a password set. The new ISR routers use cisco as the username and cisco as the password by default.
The second is an auxiliary port which is really the same thing as a console port. But an auxiliary port also allows you to configure modem commands so that a modem can be connected to the router.
It lets you dial up a remote router and attach to the auxiliary port if the router is down and you need to configure it out-of-band (meaning out of the network).
The third is Telnet, You can use Telnet to connect to any active interface on a router, such as an Ethernet or serial port.
Next Figure shows an illustration of a Cisco 2600 series modular router

The 2600 series router can have multiple serial interfaces, which can be used for connecting a T1 or Frame Relay using a serial V.35 WAN connection. Multiple Ethernet or FastEthernet ports can be used on the router, depending on the model. This router also has one console and one auxiliary connection via RJ-45 connectors.
Another router I want to talk about is the 2800 series . This router has replaced the 2600 series router series and is referred to as Integrated Services Router (ISR), because many of the services, like security, are built into it. It’s a modular device like the 2600, but it’s much faster.

 The 2800 has the Security Device Manager (SDM) preinstalled. The SDM is a Web-based device-management tool for Cisco routers that can help you configure a router via a web console.

Bringing Up a Router
When you first bring up a Cisco router,
1-      run a power-on self-test (POST).
2-      load the Cisco IOS from flash memory
3-      the IOS loads  the startup-config that’s stored in NVRAM.
4-       The startup-config will be copied from NVRAM into RAM And called  running-config.

if there isn’t a configuration in NVRAM, the router will broadcast looking for a valid one on a TFTP host. If the broadcast fails, it will then go into what is called setup mode —a step-by-step process to help you configure the router.
You can also enter setup mode at any time from the command line by typing the command setup
from privileged mode.
Command-Line Interface (CLI)
To use the CLI, press Enter after the router finishes booting up. After you do that, the router will respond with messages that tell you all about the status of each and every one of its interfaces and then display a banner and ask you to log in.
Entering the CLI from a Non-ISR Router
After the interface status messages appear and you press Enter, the Router> prompt will appear. This is called user exec mode (user mode), and it’s mostly used to view statistics, but it’s also a stepping stone to logging in to privileged mode.
You can only view and change the configuration of a Cisco router in privileged exec mode (privileged mode), which you can enter with the enable command.
Here’s how:
You now end up with a Router# prompt, which indicates that you’re in privileged mode, where you can You can go back from privileged mode into user mode by using the disable command:
At this point, you can type logout from either mode to exit the console:
Router con0 is now available
Press RETURN to get started.

Overview of Router Modes
global configuration mode: you can enter global configuration mode by typing  configure terminal (or config t for short) in which  you can make global changes to the router and changes the running-config.
A global command (a command run from global config) is set only once and affects the entire router.
To change the startup-config—the configuration stored in NVRAM—you use the configure memory command (or config mem for short), which merges the startup-config file into the running-config file in RAM.
If you want to change a router configuration stored on a TFTP host you use the configure network command (or config net for short), which also merges the file with the running-config file in RAM.

CLI Prompts
It’s really important that you understand the different prompts you can find when configuring a
Editing and Help Features
You can use the Cisco advanced editing features to help you configure your router. If you type in a question mark (?) at any prompt, you’ll be given a list of all the commands available from that prompt:

By typing the clock ? command, you’ll get a list of the next possible parameters and what they do. Notice that you should just keep typing a command, a space, and then a question mark until (carriage return) is your only option.

If you’re typing commands and receive
yourname#clock set 11:15:11
% Incomplete command.
Means  the command isn’t done yet. Just press the up arrow key to redisplay the last command entered, and then continue with the command by using your question mark.

And if you receive the error
yourname(config)#access-list 110 permit host
% Invalid input detected at ‘^’ marker.
Means you’ve entered a command incorrectly. See that little caret—the ^? It’s a very helpful tool that
marks the exact point where you blew it and entered the command incorrectly.

Here’s another example of when you’ll see the caret:
yourname#sh serial 0/0/0
% Invalid input detected at ‘^’ marker.
The problem is that the full command is show interface serial 0/0/0.

Now if you receive the error
yourname#sh ru
% Ambiguous command: “sh ru”
means there are multiple commands that begin with the string you entered . Use the question mark to find the command you need:
yourname#sh ru?
rudpv1 running-config

Table 4.2 lists the enhanced editing commands available on a Cisco router.
Next TABLE  Enhanced Editing Commands

You can review the router-command history with the commands shown in Table below.

The following example demonstrates the show history command and how to change the history size, as well as how to verify it with the show terminal command. First, use the show history command to see the last 20 commands that were entered on the router:
yourname#show history
Now use the show terminal command to verify the terminal history size:
yourname#show terminal
[output cut]
Editing is enabled.
History is enabled, history size is 20.
[output cut]

The terminal history size command, used from privileged mode, can change the size of the history buffer:
yourname#terminal history size ?
<0-256> Size of history buffer
yourname#terminal history size 25
You verify the change with the show terminal command:

Gathering Basic Routing Information
The show version command will provide basic configuration for the system hardware and the software version and the boot images. Here’s an example:
yourname#show version

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