Filed under Cisco

Cisco IOS Lab Emulator Dynamips/Dynagen/GNS3

These are some very cool and innovative tools for emulating (not simulating) a Cisco Lab with real IOS images.  The first thing you’ll want to look into is:

Dynagen/Dynamips

Internetwork Expert Tutorial

then…

GNS3

and then…

hacki.at – cisco lab forum

then some…

blindhog.net – tutorials

courtesy of…

Cisco Blog

Cisco Subnet @ Network World

How To: Perform Password Recovery on Cisco 2900 Series Switch

I have been experimenting with a new Cisco Switch that I got today.  Here is the model:

Cisco WS-C2924C-XL-EN Catalyst 2900 XL 24 port Switch

This switch has 8MB of DRAM and 4MB of system flash.  This switch was also purchased used from eBay and therefore comes with a sort of “use at your own risk” mentality.  Incidentially, it also comes with a “configure at your own risk” mentality.  This is a perfect example because this switch came with some hardcore configurations that I have never seen before – we’re talking very strong security here!

The first thing I did was look up how to do password recovery from Cisco, the link is here.

That’s all fine and dandy.  And by the way the reason I needed to do this was not only because the switch had passwords to the IOS that were unknown to me, but it also had a local username and password (detailed here) database setup.  This meant that I could not even access the CLI unless I could authenticate at the local username level.  Ugh.

So anyway, once I was able to access the CLI via the password recovery article noted above, I had to figure out how to get rid of that stupid local username database.  Referencing the Petri article, I typed the following command at the PRIVILEGED EXEC mode:

username admin priv 15 password cisco

I changed all of the other passwords to the default, cisco, and then wrote to memory via “write mem“.  I reloaded via “reload“.  Once the switch came back up, I entered my new local username and password and – I was in!  Then I simply did a “write erase” and reloaded the switch again.  All was well again and I could start fresh.

It’s imperative that you wait until you have reloaded the switched, and logged into the CLI under normal operating conditions before you “write erase” the device.  Otherwise it won’t work and you’ll be left with the same problem as before.

I hope this helps anyone out there who is sort of new to configuring and managing these devices, like me.

CCNA Subnetting Notes

*This post is for people who know about subnetting and are studying for the CCNA.

Once you start practicing for the CCNA in subnetting, you’ll realize that there are a few things you’ll have to memorize cold to do it quickly:

  • The Binary Subetting Table
  • All of the multiples of 2, 4, 8, 16, 32, 64, and 128 up to 256 for each
  • The magic number from a subnetted subnet mask octet (e.g. 255.255.248.0 magic # is 8 )
  • How many subnets and hosts per subnet for the given subnet mask

You have to be able to look at an IP address and subnet mask and in less than 10 seconds be able to determine the resident subnet of that IP address.

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