We all know the importance of SSH, and it is one of most used method for remote access of Cisco Devices either it might be a Cisco Router or a Cisco Switch. Most of the Network Engineers I come across say it is so complicated to either enable or disable the SSH in Cisco Devices.

 If you simply try to use “no commands” used to enable SSH it will not work. Here is the tip to disable the SSH in either Cisco Router or Cisco Switches.

 Commands used to enable SSH in a Cisco Device

ITKE-AS1(config)#ip domain-name itke.com

ITKE-AS1(config)#crypto key generate rsa general-keys modulus 512

The name for the keys will be: ITKE-AS1.itke.com

% The key modulus size is 512 bits

% Generating 512 bit RSA keys, keys will be non-exportable…[OK]

ITKE-AS1(config)#

ITKE-AS1(config)#aaa new-model

ITKE-AS1(config)#aaa authentication login default local

ITKE-AS1(config)#aaa authentication exec default local

Commands used to disable SSH in a Cisco Device

Do notice if you use the command “no crypto key generate rsa” it will not work rather the device will suggest you to use the ‘crypto key zeroize rsa’ command, amazing isn’t it

ITKE-AS1(config)#no crypto key generate rsa

% Use ‘crypto key zeroize rsa’ to delete signature keys.

ITKE-AS1(config)#crypto key zeroize rsa

% All RSA keys will be removed.

% All router certs issued using these keys will

will also be removed.

Do you really want to remove these keys? [yes/no]: yes

ITKE-AS1(config)#

PuTTY doesn’t need any introduction as its one of the widely used for remote console utility. PuTTY is an SSH and telnet client.

In day to day operational activities we do telnet or SSH to our Cisco routers or Switches, at times we need to backup a running or startup config or   a Cisco router or a switch or even some times we need to capture the terminal session logs for technical information etc.  This is can be easily done by using the PuTTY client.

I will show you how to capture a text using PuTTY client.

Once you have established a remote session with a Cisco router or a Switch, follow the following steps

Step 1: Right Click on the menu bar and select “Change Settings”

Step 2: Click logging under the icon Session.

Step 3: Then select “All Session Output”.

Step 4: Select the location using the browse button and enter the desired file name and click apply.

These steps will create the log file in the specified location and it will log everything you did in that particular telnet or SSH session.

We all work remotely with Cisco routers and Switches, we often do login to do some configuration changes in the Cisco routers and Switches. What if we configured wrongly in the live Cisco routers and Switches which are located in the remote sites, we don’t enjoy the liberty of resetting the devices unless we have control over the power distribution.

In this scenario the “reload” command proves to be very handy and useful. Just before making any changes to the configuration we can use the “reload” command as demonstrated below

ITKE-Cisco#reload in ?

Delay before reload (mmm or hhh:mm)

ITKE-Cisco#reload in 10

System configuration has been modified. Save? [yes/no]: no

Building configuration…

[OK]

Reload scheduled in 10 minutes by yasir on vty0 (10.0.0.5)

Proceed with reload? [confirm]

ITKE-Cisco#

ITKE-Cisco#

***

*** — SHUTDOWN in 0:05:00 —

***

The above demonstrated command will reload the device in 10 minutes. After applying the “reload” command we can proceed with the configuration changes. If things go wrong and we lost connectivity

to the device, then try back after 10 minutes as the device will get reloaded with the original startup-configuration which can helps us to restore the connectivity to the device.

Once we are sure about the new configuration and its working properly without any hassles there is always a way  “reload cancel” command is there to cancel the reload.

ITKE-Cisco#reload cancel

I find this command to be very handy and useful especially when we have to telnet or SSH to remote Cisco router or a Switch.