1 Feb 2013

Network fundamentals - Basic configuration of networking devices

3 comments
   In this post I will start some basic networking device configuration. In this post I will use Cisco Packet Tracer software (http://www.cisco.com/web/learning/netacad/course_catalog/PacketTracer.html) because it is easy to use and you can do a whole bunch of stuff with it. After this post I will create a video tutorial in which I will put all things described here, in practice. Packet Tracer offers you some very cool features, you can implement, configure, test and troubleshoot networks. Cisco did a very good job with this software because network equipment is emulated and all commands needed to configure devices are implemented.
   The Cisco IOS (Internetwork Operating System) is stored in the flash memory of devices. Switches and routers use IOS and through it administrators can configure everything from basic configuration, routing, switching, WAN connections, Security, QoS etc. But how can you access a device IOS? Well, we have talked in the previous post about the types of interfaces that a network device can have. Remember that I've told you that the console port is used to physical connect a computer to a switch or a router. You have to use a rollover cable (it is a special cable that have with a RJ-45 connector on one side and a VGA connector on the other side). This type of connection is made usually when you first configure a device. In a normal situation a network administrator uses a remote connection to configure and troubleshoot a router or a switch. In case of network failure, the only way to access a device is through a console connection. You can establish a remote connection with a device trough either aux port or telnet/ssh. Aux port is used to connect a modem (a dial-up connection) and telnet/shh connection is made through the IP protocol.
   Every network device has a processing unit (CPU), a RAM memory (Random Access Memory) and a NVRAM (Non Volatile Random Access Memory). RAM is used to store the running configuration file and NVRAM stores the start-up configuration file. The difference between these two files is that the running configuration file is lost upon system reset while start-up configuration file is loaded from NVRAM after a system reboot. When you start a router, the start-up configuration file is loaded, but if you make changes to the router configuration you actually configure the running configuration file. When you finish configuring the device you have to save the running-configuration file in the NVRAM so that the start-up configuration file is replaced with the new, updated file.
When you first boot up a router you will see the following prompt:
Cisco IOS loading screen

   The IOS is loaded and then you are prompted to configure the equipment, for now type no and press enter:
System Configuration Dialog


   After this step is complete you are entered into the User executive mode. The prompt for this mode looks like this:
System Configuration Dialog

   This configuration mode offers limited options, to have more options available you have to enter more advanced modes. Cisco devices have three more configuration modes. When you are at the User executive mode type enable to enter the User privileged mode. You will see that the prompt is automatically changed:
enable command

   To exit the User privileged mode type disable to return to the User executive mode. If you want to enter the advanced mode also called Global configuration mode type configure terminal or conf t and press TAB key while you are in the User privileged mode. The TAB key is very useful when configuring network devices because it offers you the auto-complete feature. If you don't remember a command's full name, just type the first letter and press TAB key repeatedly. Cisco IOS will display the available commands. There is another configuration mode but I will show it to you when we will configure console connection.
   Now let's start with some basic configuration. From the user executive mode let's configure the clock:
configure clock on cisco devices

   As you can see the command is clock set hh:mm:ss <1-31> MONTH Year . After I have typed clock set, I've put the ? sign. This is used to display information about a command or help. Use ? whenever you don't remember what are the elements of a command. 
   Now let's see the running-config file information by typing show running-config:
show running-config

  To see the start-up config file type : Router#show startup-config. To see all show available commands type show ? and the press enter:
show startup-config
   You can try each command because sooner or later we will use almost all of them. Try the following to see the results : show version,show terminal, show flash, show ip interface and show ip interface brief.
OK, now let's put a name to this router, let's call it RouterIT. We can change a name of a device from the global configuration mode. First let's type configure terminal to enter this mode. Now type ? and press enter:
configure terminal

  You can see there is a command called hostname. This command is used to change a Cisco device name. Type hostname RouterIT, you will see that the name is changed automatically:
how to configure hostname on Cisco router

   OK, now let's put a welcome and a log in message, also called a banner. You can configure a banner from the global configuration mode if you type banner ? and press enter:
IOS banner command

   Here you can see the two types of banner messages, the login and the motd banner. Now do the following:
Cisco banner

   The massage of a banner must be enclosed by a special character, I use the # sign. You can see that I have configured the login banner with the Welcome message and the motd banner with the This is the IT router message.
Now let's try to configure a password on the global configuration mode. Type enable ? and press enter:
enable command Cisco

   Usually you configure only one of them because they both have the same effect. The difference between these two is that the secret password command is encrypted while the password command is written in clear text. Let's configure both of them with password it, just to see the difference between them:

   Now let's vizualise the changes we have made. First type end to return to the User privileged mode and now type show running-config:
show running-config
   You can see the things that we have configured. Now, to save the running-config over the start-up config, type copy running-config startup-config:
copy running-config startup-config
   The same thing happens if you type wr (write):
copy running-config startup-config

   Now we have saved the configuration file. Type exit two times to go back to the welcome screen. If we try now to access the user privileged mode, we are asked to enter the password. Type it and you will enter. 
   Enter the global configuration mode by tying configure terminal. When you use packet tracker to configure devices, you are configuring them as if you were connected via the console port. If you remembered, the console port is used to configure a device when you are connected physically with a rollover cable. Let's configure a console password. When you are in the global configuration mode, type line console 0 and press enter:
line console 0

   This is the last configuration mode, also called specific configuration mode. You can type ? and press enter to display the available commands. I will put router, the console password. Now we have to type in the login mode. This command refers to how a user is logged in. There are three ways to configure this in IOS: by using authentication login, local login or simple login. You can see them if you type login ? and then press enter:
line console 0

   Authentication uses the aaa method list, the login local uses the locally created username and password and login uses the console created password. I will use the console created password so I will type login. Now type exit until you see the welcome banner. Now, if you try to enter the router, you will be prompted to enter the password, which in our case is router:
Cisco console lines

   I will show you one more configuration command, the local username and password. From the global configuration mode type username administrator password router:
   If you type show running-config from the User privilege mode, you will see the newly configured username and password:
show running-config

   Now, if you configure the login mode from the console line to be login local, you will have to use the locally created username and password to log in.
   In the next post I will continue showing some basic Cisco IOS configuration commands and a short video in which I want to practice everything that I've described here. Meanwhile have a nice day :)
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3 comments :

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