Note that this was originally posted in May 2009
I wrote this document to help with my CCNA studies, the intent of the document was to help me quickly convert class A and B subnets for the test. The CCNA will present subnet questions in CIDR format and you should know how to answer them in less then 90 seconds.
I converted the document from Microsoft Word 2007 to PDF using doPDF6.3 a free PDF converter. So far it appears to have done a nice job. You can find it here >Do PDF
The document is here > The Last Subnet How2 Doc
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(Last edited by rstaples on 2012-08-08 -corrected download links)
Network Address Translation, sometimes called Network Address Translator (NAT), was originally outlined in RFC 1631 in 1994. This was to allow devices on the inside network the use of private IP addresses that are presently defined in RFC 1918. NAT makes it possible to have a very big internal network with thousands of local addresses represented by a handful of global addresses or possibly a single global address.
We will setup a basic static and dynamic NAT configuration.
To the left we have a basic example of how NAT operates. Starting from the bottom we have our …
- Inside Local Addresses
- Outside Local Address
- Inside Global Address
- Outside Global Address
Our ISP has given us the following IP range. 188.8.131.52/29, looking at this subnet we can tell that our network starts on the 8th subnet range and this will give us 6 usable addresses
(For simplicity we will not be using subnet-zero)
- Network ID: 184.108.40.206 (Will always be even)
- First usable address: 220.127.116.11 (Will always be odd)
- Last usable address: 18.104.22.168 (Will always be even)
- Broadcast address: 22.214.171.124 (Remember BrODDcast, always odd)
- Netmask of: 255.255.255.248
For more subnet information refer to The Last Subnet Doc
By now I’m sure you’ve already read several articles that explained the pitfalls of using telnet to access your network devices, it’s not a secure way to access your network. Telnet does not offer any encryption, your login and password information is sent across the network in plain text.
Many Cisco devices today allow for SSH configuration. SSH not only allows for encryption of password and login information but also allows you devices to know who is logging in.
SSH can be configured easily on any Cisco device with IOS that supports DES or DES3 (should be using DES3).
Router (config) #username Joe password j03adM1n
Router (config) # ip domain-name mylab.local
Router (config) # crypto key generate rsa
Router (config) # line vty 0 4
Router (config-line) # transport input ssh
Router (config-line) # login local
Once you have your router configured for SSH, you will need to use a terminal program that supports SSH, such as PuTTY, Tera Term or SecureCRT. Windows XP and Vista include a command line SSH capability, my personal favorite is SecureCRT.