Configuring SSH on Cisco Router

This configuration is based on router with 3600 Software (C3640-JK9O3S-M), Version 12.2(6a) but it may applies to Cisco IOS 12.1(3)T and later.

Configure hostname to your router.
Router(config)# hostname hostname

Configure domain name
Router(config)#ip domain-name domainname

To automatically enables SSH, generate RSA key pair.
Router(config)# crypto key generate rsa

Type the size of key modulus in the range of 360 to 2048.
Typing 512 may takes few minutes.
How many bits in the modulus [512]: 768
% Generating 768 bit RSA keys ...[OK]
Router(config)#
*Mar 16 01:20:15.440: %SSH-5-ENABLED: SSH 1.5 has been enabled

You can change ssh setting if you wish.
Time-out should not exceed 120s which is the default. 
Authentication retries should not exceed 5,default is 3.

Router(config)# ip ssh {[timeout seconds] |[authentication-retries integer]}

Verifying SSH
Router# show ip ssh
SSH Enabled - version 1.5
Authentication timeout: 120 secs; Authentication retries: 5
Router# show ssh
%No SSH server connections running.