11.2.4.6 Lab – Accessing Network Devices with SSH - Answers

Certification Answers

11.2.4.6 Lab – Accessing Network Devices with SSH (Instructor Version – Optional Lab)

Instructor Note: Red font color or gray highlights indicate text that appears in the instructor copy only. Optional activities are designed to enhance understanding and/or to provide additional practice.

Topology

Addressing Table

Device Interface IP Address Subnet Mask Default Gateway
R1 G0/1 192.168.1.1 255.255.255.0 N/A
S1 VLAN 1 192.168.1.11 255.255.255.0 192.168.1.1
PC-A NIC 192.168.1.3 255.255.255.0 192.168.1.1

Objectives

  • Part 1: Configure Basic Device Settings
  • Part 2: Configure the Router for SSH Access
  • Part 3: Configure the Switch for SSH Access
  • Part 4: SSH from the CLI on the Switch

Background / Scenario

In the past, Telnet was the most common network protocol used to remotely configure network devices. Telnet does not encrypt the information between the client and server. This allows a network sniffer to intercept passwords and configuration information.

Secure Shell (SSH) is a network protocol that establishes a secure terminal emulation connection to a router or other networking device. SSH encrypts all information that passes over the network link and provides authentication of the remote computer. SSH is rapidly replacing Telnet as the remote login tool of choice for network professionals. SSH is most often used to log in to a remote device and execute commands; however, it can also transfer files using the associated Secure FTP (SFTP) or Secure Copy (SCP) protocols.

The network devices that are communicating must be configured to support SSH in order for SSH to function. In this lab, you will enable the SSH server on a router and then connect to that router using a PC with an SSH client installed. On a local network, the connection is normally made using Ethernet and IP.

Note: The routers used with CCNA hands-on labs are Cisco 1941 Integrated Services Routers (ISRs) with Cisco IOS Release 15.2(4)M3 (universalk9 image). The switches used are Cisco Catalyst 2960s with Cisco IOS Release 15.0(2) (lanbasek9 image). Other routers, switches, and Cisco IOS versions can be used. Depending on the model and Cisco IOS version, the commands available and the output produced might vary from what is shown in the labs. Refer to the Router Interface Summary Table at the end of this lab for the correct interface identifiers.

Note: Make sure that the routers and switches have been erased and have no startup configurations. If you are unsure, contact your instructor.

Instructor Note: Refer to the Instructor Lab Manual for the procedures to initialize and reload devices.

Required Resources

  • 1 Router (Cisco 1941 with Cisco IOS Release 15.2(4)M3 universal image or comparable)
  • 1 Switch (Cisco 2960 with Cisco IOS Release 15.0(2) lanbasek9 image or comparable)
  • 1 PC (Windows 7 or 8 with terminal emulation program, such as Tera Term, and Wireshark installed)
  • Console cables to configure the Cisco IOS devices via the console ports
  • Ethernet cables as shown in the topology

Part 1: Configure Basic Device Settings

In Part 1, you will set up the network topology and configure basic settings, such as the interface IP addresses, device access, and passwords on the router.

Step 1: Cable the network as shown in the topology.
Step 2: Initialize and reload the router and switch.
Step 3: Configure the router.

a. Console into the router and enable privileged EXEC mode.

b. Enter configuration mode.

c. Disable DNS lookup to prevent the router from attempting to translate incorrectly entered commands as though they were host names.

d. Assign class as the privileged EXEC encrypted password.

e. Assign cisco as the console password and enable login.

f. Assign cisco as the VTY password and enable login.

g. Encrypt the plaintext passwords.

h. Create a banner that will warn anyone accessing the device that unauthorized access is prohibited.

i. Configure and activate the G0/1 interface on the router using the information contained in the Addressing Table.

j. Save the running configuration to the startup configuration file.

Step 4: Configure PC-A.

a. Configure PC-A with an IP address and subnet mask.

b. Configure a default gateway for PC-A.

Step 5: Verify network connectivity.

Ping R1 from PC-A. If the ping fails, troubleshoot the connection.

Part 2: Configure the Router for SSH Access

Using Telnet to connect to a network device is a security risk because all information is transmitted in a clear text format. SSH encrypts the session data and provides device authentication, which is why SSH is recommended for remote connections. In Part 2, you will configure the router to accept SSH connections over the VTY lines.

Step 1: Configure device authentication.

The device name and domain are used as part of the crypto key when it is generated. Therefore, these names must be entered prior to issuing the crypto key command.

a. Configure device name.

Router(config)# hostname R1

b. Configure the domain for the device.

R1(config)# ip domain-name ccna-lab.com
Step 2: Configure the encryption key method.
R1(config)# crypto key generate rsa modulus 1024
The name for the keys will be: R1.ccna-lab.com

% The key modulus size is 1024 bits
% Generating 1024 bit RSA keys, keys will be non-exportable...
[OK] (elapsed time was 1 seconds)

R1(config)#
*Jan 28 21:09:29.867: %SSH-5-ENABLED: SSH 1.99 has been enabled
Step 3: Configure a local database username.
R1(config)# username admin privilege 15 secret adminpass

Note: A privilege level of 15 gives the user administrator rights.

Step 4: Enable SSH on the VTY lines.

a. Enable Telnet and SSH on the inbound VTY lines using the transport input command.

R1(config)# line vty 0 4
R1(config-line)# transport input telnet ssh

b. Change the login method to use the local database for user verification.

R1(config-line)# login local
R1(config-line)# end
R1#
Step 5: Save the running configuration to the startup configuration file.
R1# copy running-config startup-config
Destination filename [startup-config]?
Building configuration...
[OK]
R1#
Step 6: Establish an SSH connection to the router.

a. Start Tera Term from PC-A.

b. Establish an SSH session to R1. Use the username admin and password adminpass. You should be able to establish an SSH session with R1.

Part 3: Configure the Switch for SSH Access

In Part 3, you will configure the switch in the topology to accept SSH connections. After the switch has been configured, establish an SSH session using Tera Term.

Step 1: Configure the basic settings on the switch.

a. Console into the switch and enable privileged EXEC mode.

b. Enter configuration mode.

c. Disable DNS lookup to prevent the router from attempting to translate incorrectly entered commands as though they were host names.

d. Assign class as the privileged EXEC encrypted password.

e. Assign cisco as the console password and enable login.

f. Assign cisco as the VTY password and enable login.

g. Encrypt the plain text passwords.

h. Create a banner that will warn anyone accessing the device that unauthorized access is prohibited.

i. Configure and activate the VLAN 1 interface on the switch according to the Addressing Table.

j. Save the running configuration to the startup configuration file.

Step 2: Configure the switch for SSH connectivity.

Use the same commands that you used to configure SSH on the router in Part 2 to configure SSH for the switch.

a. Configure the device name as listed in the Addressing Table.

b. Configure the domain for the device.

S1(config)# ip domain-name ccna-lab.com

c. Configure the encryption key method.

S1(config)# crypto key generate rsa modulus 1024

d. Configure a local database username.

S1(config)# username admin privilege 15 secret adminpass

e. Enable Telnet and SSH on the VTY lines.

S1(config)# line vty 0 15
S1(config-line)# transport input telnet ssh

f. Change the login method to use the local database for user verification.

S1(config-line)# login local
S1(config-line)# end
Step 3: Establish an SSH connection to the switch.

Start Tera Term from PC-A, and then SSH to the SVI interface on S1.

Are you able to establish an SSH session with the switch? __________________
Yes. SSH can be configured on a switch using the same commands that were used on the router.

Part 4: SSH From the CLI on the Switch

The SSH client is built into the Cisco IOS and can be run from the CLI. In Part 4, you will SSH to the router from the CLI on the switch.

Step 1: View the parameters available for the Cisco IOS SSH client.

Use the question mark (?) to display the parameter options available with the ssh command.

S1# ssh ?
  -c    Select encryption algorithm
  -l    Log in using this user name
  -m    Select HMAC algorithm
  -o    Specify options
  -p    Connect to this port
  -v    Specify SSH Protocol Version
  -vrf  Specify vrf name
  WORD  IP address or hostname of a remote system
Step 2: SSH to R1 from S1.

a. You must use the –l admin option when you SSH to R1. This allows you to log in as user admin. When prompted, enter adminpass for the password.

S1# ssh -l admin 192.168.1.1
Password:
***********************************************
  Warning: Unauthorized Access is Prohibited!
***********************************************

R1#

b. You can return to S1 without closing the SSH session to R1 by pressing Ctrl+Shift+6. Release the Ctrl+Shift+6 keys and press x. The switch privileged EXEC prompt displays.

R1#
S1#

c. To return to the SSH session on R1, press Enter on a blank CLI line. You may need to press Enter a second time to see the router CLI prompt.

S1#
[Resuming connection 1 to 192.168.1.1 ... ]

R1#

d. To end the SSH session on R1, type exit at the router prompt.

R1# exit

[Connection to 192.168.1.1 closed by foreign host]
S1#

What versions of SSH are supported from the CLI? __________________
Answers may vary. This can be determined by using the ssh –v ? on the command line. The 2960 switch running IOS version 15.0(2) supports SSH v1 and V2.

S1# ssh -v ?
  1  Protocol Version 1
  2  Protocol Version 2

Reflection

How would you provide multiple users, each with their own username, access to a network device? __________________
Answers may vary. You would add each user’s username and password to the local database using the username command. It is also possible to use a RADIUS or TACACS server, but this has not been covered yet.

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