In recent times, there is an increasing need for organizations to give employees access to their IT facilities due to the ongoing Covid restrictions ( such as work from home )  in place and in other cases grant access to external parties like clients, vendors who want to troubleshoot and fix issues with the IT Infrastructure remotely.

More so, is the need for multiple manage SSH access to the company’s Linux servers, Routers, Switches, while meeting regulatory and security compliance. This need led to the emergence of the SSH Bastion host concept.

What is an SSH Bastion Host?                             

An SSH Bastion host is simply a single, hardened server that you “jump” through in order to access other servers or devices on the inner network.

Sometimes called a SSH Jump host , or SSH Jump Server  ssh gateway or a relay host, it’s simply a server that all of your users can log into and use as a relay server to connect to other Linux servers, Routers, Switches and more. Therefore, a SSH bastion host is a server inside a secure zone, which can be accessed from a less secure zone. It is then possible to jump from this host to greater security zones.

In other words, it is an intermediary host or an SSH gateway to a remote network, through which a connection can be made to another host in a dissimilar security zone, for example a demilitarized zone (DMZ2). In short it is intended to breach the gap between two security zones. This is done with the purpose of establishing a gateway to access something inside of the security zone, from the DMZ

The SSH Bastion host bridges two dissimilar security zones and offers controlled and monitored access between them.

For users accessing your secure network over the internet, the Bastion host provides a highly secured and monitored environment especially when it spans a private network and a DMZ with servers providing services to users on the internet.

Furthermore, a classic scenario is connecting from your desktop or laptop from inside your company’s internal network, which is highly secured with firewalls to a DMZ. In order to easily manage a server in a DMZ, you may access it via a bastion host.

Therefore, a bastion host is a server inside a secure zone, which can be accessed from a less secure zone. It is then possible to jump from this host to greater security zones. An example would be a high security zone inside a corporation. The policy guide states that this zone cannot be accessed directly from a normal user zone. Hence, in a DMZ off the firewall protecting this zone you have a jump host.

Connections are permitted to the ssh bastion host from the user zone, and access to the secure zone are permitted from the bastion host.

More often, there is a separate authentication method for the bastion host fortified with multi factor authentication, Single Sign On ( SSO ) , Radius  more. 

How does SSH with bastion work?  

It is a secure intermediary server where all your system administrators would login in first via SSH before getting to access the remote devices such as Linux instance, Routers, Switches etc. The purpose of having the SSH bastion host  is to improve security and consolidate SSH user activities to a single point hence better security and accountability. SSH bastion host is also known by the name SSH Jump Box, SSH Jump Host SSH Gateway.

How to Setup an SSH Bastion Host?

• Bastion using OpenSSH
  
        A basic ssh bastion host server with limited features and functionalities can be configured usingOpenSSH packages that are available by default on most Linux distributions.
• How do I connect to bastion ssh?

                    In the example below, we will just use the basic ssh command line to proxy an ssh connection to the remote server via an intermediate jump server.

ssh -J bastion_host remote_machine

                If the -J option is not available use the -W option to pivot the connection through an intermediate bastion host.

ssh -o ProxyCommand="ssh -W %h:%p bastion.gateway.org"  remote.server.org

            You can also use an SSH client configuration file, instead of passing arguments via SSH.

Edit the ~/.ssh/config file :

Host nickname

HostName hostname_of_remote_server

User user_on_remote_server

ProxyCommand ssh user_on_remote_server@bastion_host nc %h %p

• nickname : Sets nickname for the target/remote server
• hostname_of_remote_sever : Sets the real remote server/host name
• user_on_remote_server : Real user who exists on target server
• bastion_host: IP or the hostname` of the proxy server
• %h will be the host name to connect
• %p will be the port

Now you can SSH to the target/remote machine:

ssh -v target/remote_server

              With the OpenSSH 7.3,  the easiest way to pass through hop through intermediate one or more jump hosts is using the ProxyJump directive ssh_config

Host remote server

   HostName 192.168.0.177

   ProxyJump admin@jump-server.org:22

   User devops

 Multiple bastion hosts can be chained as well

Host remote server

   HostName 192.168.0.177

   ProxyJump admin@jump-server.org:22, admin@jump-server2.org:22

   User devops

Bastion host usingEzeelogin
  Ezeelogin is a much more powerful and advanced SSH bastion host software solution  and  can be deployed quickly on a Linux server.  It has powerful features that  makes managing hundreds of Linux devices and granting ssh access to these devices a piece of cake.  Do refer to the article to  setup and configure a ssh bastion host  quickly on your premise or on cloud.  

Why do you need an SSH Bastion Host solution to manage ssh access? 

                          The OpenSSH based bastion host server is clearly not enough to meet the modern day requirements  of an IT enterprise. The challenges for  the enterprise are constantly changing and dynamic . It could be from maintaining security, granting ssh access to the users to designated server and that too for particular time and on another day it could be the security compliances that needs to be met at the time of a Linux servers infrastructure audit.

The modern day  SSH  bastion host solutions are designed to address the challenges faced by an IT enterprise when it comes to  security and to meet various security compliances like PCI DSS, NIST, ISO 27001 and more.

The modern day ssh bastion host  software such as Ezeelogin has the  following features  and more.

• Identity and Access management (IAM)
• Privileged Access management (PAM),
• Role Based Access Control to delegate access to Linux servers and Network devices.
• Two factor authentication methods  like Google Authenticator, DUO Security 2FA, Yubikey in SSH.
• Integrates with Windows Active Directory,OpenLDAP, Redhat IDM.
• Supports SAML for  Single Sign On.
• Support RADIUS Authentication to access network devices such as Routers and Switches
• Password Manager
• SSH key rotation, 
• Automated root password management

Importance of SSH bastion host?  

1. Improved Security
            2. Centralized Access
            3. Streamlined Access Management
            4. Compliance with Security Standards

How do I secure my SSH bastion host?

                 To ensure maximum protection of your bastion host, you should focus on the process of server security hardening. In simple terms, that means applying a combination of basic and advanced security measures to address vulnerabilities in your bastion host server and operating system to boost overall server security.

CONCLUSION

IT Enterprises that use a SSH Bastion host solution in improving security of their critical IT asset and in meeting various mandatory security compliances  (which would otherwise prove very costly in case of a breach),  are more likely to succeed due to the improved operational efficiency, digital security, hence more successful business for the company’s end customers.