SSH(Secure socket Layer/shell) Secure Shell Server
To enable secure access to your Cisco device, you can use SSH instead of Telnet which is less secure than SSH.
SSH uses encryption to secure data from eavesdropping while telnet use clear text username and password which can be hacked or sniffed by hackers easily. So i recommend you to use SSH instead of TELNET. Although you can use telnet where security is not a great concern.
Configuration the SSH
Router>enable
Router#config t
Router(config)#hostname 1
1(config)#enable secret ccna
1(config)#line vty 0 4
1(config-line)#password 123
1(config-line)#login local
1(config-line)#exit
1(config)#username mypc password 456
1(config)#ip domain name mydomain.com
1(config)#crypto key generate rsa
Do you really want to replace them? [yes/no]: yes The name for the keys will be: 1.mydomain.com ,Choose the size of the key modulus in the range of 360 to 2048 for your General Purpose Keys. Choosing a key modulus greater than 512 may take a few minutes.
How many bits in the modulus [512]: 456
% Generating 456 bit RSA keys, keys will be non-exportable…[OK]
1(config)#line vty 0 4
1(config-line)#transport input ssh
1(config-line)#exit
AT PC’s Command prompt