How to Fortify Network Defenses With Bastion Hosts

July 3, 2024

A bastion host is a special-purpose computer designed to withstand attacks on a network. Like a fortress or a bouncer at a club, it's the frontline defense in an enterprise network, serving as a gateway between internal networks and the outside world. 

Typically, a bastion host is highly fortified yet minimalistic. It's hardened to resist attacks, which means you turn off unnecessary services and use the most secure configurations. 

By deploying a bastion host, you create a secure gate that protects and monitors traffic, ensuring that your enterprise network remains as safe as possible.

How does a bastion host work?

Imagine you have a web server that must be accessible from the internet. By placing it on a bastion host, you ensure that even if someone tries to hack it, they must go through this heavily guarded checkpoint first.

One common use case in enterprise networks is to place a bastion host in a DMZ (Demilitarized Zone). This is a subnetwork that exposes external services to the internet but keeps them isolated from the internal network.

Picture the DMZ as a buffer zone between your secure internal network and the dangerous outside world. For instance, if you have a database server, you'd want to keep it protected behind this buffer zone to keep the sensitive data safe.

In practice, if you’re running SSH (Secure Shell) to manage various servers, you’d typically set up a bastion host and funnel all SSH traffic through it. 

This way, only the bastion host has direct access to the internal servers, adding an extra layer of security. It’s like having a single door to a treasure room; you only need to guard one entry point instead of multiple doors.

How do you protect the bastion host itself?

Securing a bastion host involves using strong authentication methods and regular monitoring. It’s essential to keep an eye on it because, if compromised, it can become a weak point. 

For example, you might use multi-factor authentication and continuously monitor logs for unusual activity. It acts as a canary in the coal mine, alerting you to potential threats before they infiltrate deeper into your network.

Why use a bastion host in a company network?

Enhances security

The bastion host is like the heavily guarded gate. It is specifically designed to withstand attacks and scrutinize incoming traffic. By directing external traffic through this secure checkpoint, you add an extra layer of security. This means that even if someone tries to breach your network, they must first get past the bastion host.

Therefore, bastion hosts reduce the attack surface. Since they are the only points of entry, you can focus your security measures effectively. The bastion host’s stringent authentication and authorization protocols make it hard for malicious actors to infiltrate your network.

For example, you could configure the bastion host to require multi-factor authentication (MFA). Furthermore, bastion hosts often include robust logging features. They record every attempt to access the network, whether successful or not. 

The log provides invaluable data for auditing and forensics if you ever need to investigate suspicious activities. You can track exactly when and how an unauthorized access attempt was made.

The bastion host can also be configured to permit access only during certain times of the day or from specific IP addresses. For instance, if your admin team works from a particular office, you can restrict access to just that location. 

If someone tries to connect from a different IP address, they’ll be denied access. This geofencing approach adds yet another layer of security tailored to our operational needs.

Deploying bastion hosts is a strategic move to enhance network security. They act as fortified entry points, offer detailed monitoring, and drastically cut down on vulnerabilities. Using them adds strong barriers and helps you keep a watchful eye on who’s coming into your network.

Provides controlled access to internal networks

In enterprise environments, you can't just let anyone wander into your computer network. Usually placed outside the firewall or in a DMZ, the bastion host regulates access to the internal network, allowing only authorized users and keeping the bad guys out. 

So, if someone wants to access your internal database server, they first need to connect to the bastion host. Once authenticated, they can proceed further. This setup is particularly useful for remote access. 

Instead of giving remote employees direct access to the network, which increases the risk of security breaches, you make them pass through the bastion host. Only after verifying their credentials does the bastion host grant them access.

Moreover, bastion hosts are closely monitored, with logging and alerting mechanisms in place. If there's any suspicious activity, like repeated failed login attempts, you get notified immediately. For instance, if someone tries to brute force their way in, you will know about it, and can take appropriate actions swiftly.

Simplifies compliance with security standards

Using bastion hosts aids compliance with security standards and regulations. Many compliance frameworks, like PCI DSS for payment card security, require controlled access measures. Having a bastion host aligns with these requirements and keeps us compliant.

Adhering to industry security standards, such as those outlined by ISO/IEC 27001, often involves stringent access control measures. Bastion hosts assist in meeting these requirements by enforcing strict authentication and authorization protocols. 

Patch management is another area where bastion hosts are invaluable. Cyber security standards often call for regular updates and patching of systems to protect against vulnerabilities. 

Bastion hosts, being fewer in number than internal servers, are easier to manage and update regularly. This ensures that your defenses are always up-to-date, significantly reducing the risk of exploits due to unpatched software.

Incorporating bastion hosts into your network architecture aligns well with the principle of defense in depth. The principle encourages the creation of multiple layers of security that make it much harder for threats to penetrate. Each layer, including the bastion host, adds a checkpoint that an attacker must navigate, dramatically increasing your overall security posture.

Typical architecture of a bastion host

Bastion self-service

Deploying a self-service bastion host involves creating an Oracle Linux 8 virtual machine (VM), setting it up in a public subnet, and ensuring you have an internet gateway. This setup is straightforward but exposes the VM to the open internet.


With Bastion-as-a-Service, your bastion host is deployed in a private subnet, which shields it from direct exposure to the internet. Instead of your own firewall and other network defenses, you rely on your chosen cloud service’s built-in mechanisms to enforce security policies.

A useful approach is to place your bastion host in a dedicated subnet. It simplifies managing network policies and keeps your architecture clean. Also, consider using a Hub-VCN to connect multiple VCNs. It’s a powerful option, though it brings additional complexities.

Both self-service and Bastion as a Service offer robust solutions, each with their own pros and cons. The self-service route gives more flexibility, like using SSHuttle for a pseudo VPN. But with greater flexibility comes the risk of overexposing yourself to external threats if not properly managed. 

Bastion as a Service, while more restrictive, offers centralized management and the benefits of your vendor’s native IAM policies. In the end, both approaches have their unique strengths, helping you securely access resources within OCI.

Bastion host placement in network topology

Carefully placing bastion hosts and configuring them correctly in your network topology will create a robust defense mechanism. It reduces the attack surface and enhances the overall security posture of your enterprise network.

The standard practice is to place the bastion host in a DMZ. The DMZ is a subnet that sits between the public internet and your internal network. By positioning the bastion host here, you add an extra layer of security. 

Take a scenario where external users need SSH access. By routing their connections through the bastion host in the DMZ, you inspect and log these connections before they can proceed any further.

If you have a web server that needs to be accessed from the internet, a bastion host placed in the DMZ would handle all incoming requests, filter out malicious traffic, and only forward legitimate requests to the internal network. This setup mitigates the risk of direct attacks on your internal servers.

If your internal team needs to access remote services, you can also funnel all the direct outbound connections through the bastion host. Also, if you are using a cloud service, the bastion host can securely manage SSH keys and other sensitive access credentials. It acts like a checkpoint, ensuring only authorized traffic reaches the cloud resources.

Ensure that the bastion host itself is hardened. This means it's stripped down to the bare essentials to minimize vulnerabilities. For instance, the host should only run necessary services like SSH or RDP. Keep it updated with the latest security patches and employ intrusion detection systems to monitor any suspicious activities.

For high-security environments, you can use a multi-layered approach. You will have a primary bastion host in the DMZ and an additional internal bastion host. This secondary host provides another security checkpoint before any traffic reaches the core of your network. It adds another inspection station, where only the most vetted and scrutinized traffic is allowed to enter.

How the bastion host interacts with other network components

The bastion host stands at the edge, facing the brunt of incoming traffic and making decisions about what can pass. It scrutinizes every piece of data before allowing entry. But how does the bastion host interact with the other components of your WLAN?


The bastion host works hand-in-hand with your firewall. While the firewall blocks or permits traffic based on predefined security rules, the bastion host adds an extra layer of scrutiny. 

For instance, if a user wants to access a critical database, the request first goes through the firewall. If it passes, it then hits the bastion host, which further examines the details. This two-step verification ensures that only legitimate traffic makes it through.

Internal servers

After the firewall, the bastion host interacts with your internal servers. It often serves as a proxy, meaning it forwards requests from external users to internal servers. This way, the servers remain hidden, shielded from direct exposure to the internet. 

Network switches

The bastion host doesn’t directly interact with switches but its actions impact them. For instance, when the bastion host blocks malicious traffic, it reduces the load on your switches. This means they can handle legitimate traffic more efficiently.

Network monitoring tools

The bastion host can feed vital information to network monitoring tools. By logging details of every interaction, it helps you keep an eye on potential threats and unusual activities, meaning you stay informed and proactive.

The bastion host’s interaction with your network components is crucial. It helps maintain checks and balances that keep your network robust and secure.

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