Ben Paxton

Secure Shell (SSH) is a cryptographic network protocol used for secure remote access to network devices. It provides a secure channel over an unsecured network, ensuring confidentiality and integrity of data transmitted between the client and the network device. In this blog post, we will explore the steps to configure network devices for remote access using SSH, along with practical examples for Cisco devices.

Enable SSH on Network Devices:

First, we need to enable SSH on the network devices. By default, SSH might be disabled on some devices. To enable SSH, access the device’s command-line interface (CLI) through a console or Telnet session, and enter the following command:

Router(config)# crypto key generate rsa
The name for the keys will be: <hostname>
Choose the size of the key modulus in the range of 360 to 4096 for your
  General Purpose Keys. Choosing a key modulus greater than 512 may take
  a few minutes.

How many bits in the modulus [512]: 2048

This command generates an RSA key pair, used for secure communication. You can choose the key modulus size based on your security requirements.

Create User Accounts:

Next, we need to create user accounts on the network device to allow remote access. We will create a user with administrative privileges for SSH access:

Router(config)# username admin privilege 15 secret <password>

Replace <password> with a strong password for the admin user. The privilege level “15” provides full administrative access.

Configure VTY Lines:

VTY lines are used to enable remote access to the device. We will configure the VTY lines to accept SSH connections:

Router(config)# line vty 0 4
Router(config-line)# transport input ssh
Router(config-line)# login local

The “transport input ssh” command restricts VTY access to SSH connections only, and “login local” enables local authentication using the user accounts we created.

This command displays the SSH status and the version of SSH running on the device.

Connect to the Device via SSH:

Now that SSH is configured, you can use an SSH client application (such as PuTTY) to connect to the network device. Enter the device’s IP address or hostname and provide the admin user credentials when prompted.

Example:

SSH into the router:
$ ssh admin@192.168.1.1

Configuring network devices for remote access using SSH is crucial for maintaining a secure and efficient network infrastructure. By enabling SSH, creating user accounts, and configuring VTY lines, network administrators can securely manage and troubleshoot network devices from remote locations. Implementing SSH ensures that sensitive information remains confidential during data transmission, providing an essential layer of security in modern network environments.