ssh and telnet (difference )implementation

Telnet

The Telnet protocol is still broadly used but on the other hand it is valuable remembering  that it is not as secure as SSH; therefore in any situation in the real world where security is of major concern at that time SSH should always be used.

Below is the basic primary configuration of the router:

Router>en

Router#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)#hostname R1

R1(config)#enable secret cisco

R1(config)#int f0/0

R1(config-if)#ip address 192.168.0.1 255.255.255.0

R1(config-if)#no shutdown

R1(config-if)#ex

R1(config)#line vty 0

R1(config-line)#password cisco

R1(config-line)#login

R1(config-line)#exec-timeout 30

R1(config-line)#logging synchronous

R1(config-line)#motd-banner

R1(config-line)#exit

R1(config)#do copy run start

Destination filename [startup-config]?

Building configuration...

[OK]

R1(config)#

1) elected to have only a single line (hence the line vty 0); if you want more lines then the command would read something like: line vty 0 4 - this would give me a total of 5 lines (lines 0 through 4).

2) The exec-timeout command just sets the time-out limit on the line from the default to 30 minutes. The shorter time-out can be annoying when configuring several devices at once.

3) The logging synchronous command stops any message output from splitting your typing

 4) the motd-banner forces a banner message to appear when logging in. 

SSH

Configuring SSH is identical to Telnet. The key difference is the generation of the crypto key; the basic line parameters are the same:

Router>en

Router#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

Router(config)#hostname R2

R2(config)#enable secret cisco

R2(config)#int f0/0

R2(config-if)#ip address 192.168.10.1 255.255.255.0

R2(config-if)#no shutdown

R2(config-if)#ex

R2(config)#ip domain-name steve.local

R2(config)#crypto key generate rsa

The name for the keys will be: R2.steve.local

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]: 512

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

R2(config)#ip ssh time-out 30

R2(config)#ip ssh authentication-retries 5

R2(config)#line vty 0

R2(config-line)#transport input ssh

R2(config-line)#login

% Login disabled on line 66, until 'password' is set

R2(config-line)#password cisco

R2(config-line)#logging synchronous

R2(config-line)#motd-banner

R2(config-line)#exit

Domain name and  the hostname; these two variables will form the basis of the key generation.therefor these variable are important to form 

after executing 

R2(config)#username steve password tiddles

R2(config)#line vty 0

R2(config-line)#login local

R2(config-line)#exit