Lab 58: Configuring SSH Access/Disable Telnet Access

Lab Objective:

The objective of this lab exercise is for you to learn and understand how to configure a router or switch for SSH access. Your router or switch IOS must support encryption in order for the commands to work. You should see a k9 in the image name as well as a security statement from Cisco saying “This product contains cryptographic features…”.

Lab Purpose:

Protecting your Cisco devices by disabling Telnet and enabling SSH-only access is a core security step, as well as a CCNA exam requirement.

Certification Level:

This lab is suitable for CCENT certification exam preparation.

Lab Difficulty:

This lab has a difficulty rating of 7/10.

Readiness Assessment:

When you are ready for your certification exam, you should complete this lab in no more than 5 minutes.

Lab Topology:

Please use any single router or switch to complete this lab so long as it has the correct IOS image.

Task 1:

Attach a PC to a router using a switch or crossover cable and add the IP settings above to the devices. Configure any desired hostname on your device.

Task 2:

Configure a username and password on your router. Disable Telnet access on the VTY lines and enable SSH access.

Task 3:

Configure the router to use SSH with the settings below:

  • Doman name:
  • 1024 modulus SSH timeout: 60 seconds
  • Authentication retries: 2
  • SSH version 2

Task 4:

Disable HTTP (Hypertext Transfer Protocol) access to the router. Issue the appropriate show commands to check your SSH settings.

Task 5:

Connect to the router using a PC with SSH.

Configuration and Verification

Task 1:

For reference information on configuring hostnames and IP addresses, please refer to earlier labs.

For the PC (if you are using Packet Tracer):

Task 2:

R1(config)#username howtonetwork password cisco 
R1(config)#line vty 0 15 
R1(config-line)#transport input ? 
all     All protocols 
none    No protocols 
ssh     TCP/IP SSH protocol 
telnet  TCP/IP Telnet protocol 
R1(config-line)#transport input ssh 

This command will also disable Telnet.

Task 3:

R1(config)#ip domain-name 
R1(config)#crypto key generate rsa 
The name for the keys will be: 
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]: 1024 
% Generating 1024 bit RSA keys, keys will be non-exportable...[OK] 

R1(config)#ip ssh time-out ? 
 <1-120>  SSH time-out interval (secs) 
R1(config)#ip ssh time-out 60 
R1(config)#ip ssh authentication-retries  2 
R1(config)#ip ssh version 2

Task 4:

R1(config)#no ip http server 

R1#show ip ssh 
SSH Enabled - version 2.0
Authentication timeout: 60 secs; Authentication retries: 2 
R1#show crypto key ? 
mypubkey  Show public keys associated with this router 
R1#show crypto key my 
R1#show crypto key mypubkey rsa 
% Key pair was generated at: 0:2:58 UTC Mar 1 1993 
Key name: 
Storage Device: not specified 
Usage: General Purpose Key 
Key is not exportable. 
Key Data: 
6af47136  7dfa1d2d  53435e72  197f4ed8  229d6342  5c5b3b19  601bbae0  18491391 
7d676c5e  3f4e6cb4  32e2f903  31b53943  40cb31ea  5d2552b3  00160600  77791266 
51180b5a  4f759502  5df3ea6c  4ffda4fc  4b5351bb  11f16ac4  2374aeb6  44f60c4e 
% Key pair was generated at: 0:2:58 UTC Mar 1 1993 
Key name: 
Temporary key 
Usage: Encryption Key 
Key is not exportable. 
Key Data: 
6b8a0260  167f96e7  117d29b7  58907508  704e7231  637db8c1  25a136f0  5b42e367 6177d5ee
78e49562  74c2323f  04153930  553fd07b  54dded20  1c5e4cc1  52a73cda 142c59d4  4f4145c4 
045c761d  54f78bbe  2c669877  04727c1e  4c709e24  7d7ea3d2 Task 5: PC>ssh -l paul

Task 5:

PC>ssh -l paul

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