While upgrading my IOS, I was getting the error message that there is not enough space available for the new IOS. I was issuing the following command:

Certhacker#copy tftp flash:
Address or name of remote host [192.168.1.1]?
Source filename [c2600-i-mz.121.T.bin]? c2600-i-mz.121-1.T.bin
Destination filename [c2600-i-mz.121-1.T.bin]?
Loading c2600-i-mz.121-1.T.bin from 192.168.1.1 (via Serial0/0): !
%Error copying tftp://192.168.1.1/c2600-i-mz.121-1.T.bin (Not enough space
on device)
Certhacker#

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First we look at what exactly NAT is? It means Network Address Translation. This technology or technique was developed to overcome the shortage of public IP addresses in IPv4 standard. With the invent of NAT, the problem of shortage of public IP addresses has been solved quite a bit. Now we have moved to IPv6 which has a lot more addresses than IPv4 but still most of the world uses IPv4 in combination with NAT.

If anyone wants to dig down deep to understand NAT, he can go to the following Wikipedia article:

http://en.wikipedia.org/wiki/Network_address_translation

Now let’s start by configuring a basic NAT on a Cisco router. The type of NAT we are going to configure here is Overloading. This means that we will map one public IP address to many private or local IP addresses.

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This is a fairly easy question but if you’re a newbie in Cisco routers, then this can be a handy guide to tell you the details.

To see the version of IOS, there is one command which give a detailed overview of the software installed on the system (Cisco router or switch).Lets issue the command:

Certhacker#show version

The following sample information will be shown:

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As the title suggests, I want to have a limited access to my router through telnet. I want only specific networks to be able to telnet my router. All others should be blocked from telnetting the router.

So let’s start:

Enter global config mode

Certhacker#configure terminal
Enter configuration lines, one per line. End with CNTL/Z
Certhacker(config)#

Create Access list to permit a network

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Hostname is the name of the router. It’s up to us what we name it. It’s like giving a name to our own systems. If we are using a command line interface to access the router or switch, then we can see the current name of the device before the prompt.

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SSH is the preferred protocol for remote communication with Cisco products. SSH is more secure than Telnet because all the data is sent with encryption.

To see if SSH in Cisco router or switch is enabled or not issue the following command:

Certhacker#show ip ssh

%SSH has not been enabled

You can see that SSH has not been enabled on the router or switch. To enable SSH do the following:

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