Inline security appliances are essential defenses for modern networks. Intrusion Prevention Systems (IPS), next-generation firewalls, Data Loss Prevention (DLP) tools, and SSL inspection devices all sit directly in the path of live traffic, inspecting and acting on every packet that passes through. That inline position gives them power. It also creates a critical vulnerability: if the appliance fails, crashes, or needs maintenance, your network traffic stops flowing.
A bypass TAP solves this problem by acting as a protective guardian between your inline security tools and your live network. When a connected appliance goes offline for any reason, the bypass TAP automatically reroutes traffic around it, keeping your network running without interruption. When the appliance comes back online, traffic is seamlessly redirected back through it.
This article explains what bypass TAPs are, how they work, where they fit in your network architecture, and why organizations that run inline security tools consider them essential infrastructure.
To understand why bypass TAPs exist, you need to understand the fundamental risk of inline security deployment.
When a security tool operates inline, it sits physically between two network segments. Every packet traveling from one side to the other must pass through the appliance before continuing. This gives the tool the ability to inspect, block, or modify traffic in real time.
The challenge is what happens when that inline device fails. Unlike out-of-band monitoring tools, which simply observe a copy of traffic without affecting the live network, an inline appliance that goes down can bring the entire network segment with it.
Inline appliance failures happen more often than most teams anticipate. Common triggers include:
Without a bypass TAP in place, any of these events creates a network outage. Traffic stops flowing, users lose connectivity, and applications go offline until the problem is resolved.
Many organizations face a difficult trade-off when deploying inline security tools. They can prioritize security by keeping the appliance in the traffic path at all times, accepting the risk of outages. Or they can prioritize availability by routing around the tool during problems, accepting the security gap that creates.
A bypass TAP removes this trade-off entirely. It keeps the appliance in the traffic path when it's functioning and automatically routes around it when it's not.
A bypass TAP inserts itself into the network link between two endpoints, with the inline security appliance connected on a separate pair of ports. This creates two possible traffic paths: through the appliance, or directly between the two network segments.
During normal operation, the bypass TAP forwards all traffic through the connected security appliance. The appliance inspects each packet and either passes it, modifies it, or drops it according to its configured policies. From the network's perspective, the appliance is functioning as expected.
The mechanism that makes automatic failover possible is heartbeat monitoring. The bypass TAP continuously sends test signals, known as heartbeat packets, to the connected security appliance. These signals travel through the appliance and return to the TAP, confirming that the device is active and able to process traffic.
The heartbeat cycle happens at a configurable interval, typically every few hundred milliseconds. As long as the appliance continues returning heartbeat packets within the expected timeframe, the bypass TAP maintains the inline traffic path.
If the appliance stops returning heartbeat packets, the bypass TAP immediately detects the failure. It activates its internal bypass relay, creating a direct connection between the two network segments that routes traffic around the failed appliance. This failover happens in milliseconds, minimizing any disruption to network users.
The bypass TAP continues sending heartbeat packets to the appliance even during bypass mode. When the appliance recovers and begins responding again, the TAP detects the restored heartbeat and seamlessly redirects traffic back through the device.
Bypass TAPs and standard network TAPs both connect to your physical network infrastructure, but they serve distinct purposes.
A standard network TAP connects to a network link and creates a copy of all traffic passing through it. That copy is forwarded to connected monitoring tools, such as network analyzers, intrusion detection systems, or Security Information and Event Management (SIEM) platforms. The original traffic continues flowing normally through the live link. Standard TAPs don't interact with the traffic path at all.
A bypass TAP sits in the live traffic path and controls whether traffic flows through an inline appliance or directly between network segments. It doesn't just observe traffic. It actively manages it.
Many organizations deploy both types. Standard TAPs feed out-of-band monitoring tools with traffic copies, while bypass TAPs protect the inline security tools that actively intercept and filter live traffic.
Bypass TAPs are deployed wherever inline security appliances connect to your network. The exact placement depends on which tools you're protecting and where those tools are positioned in your architecture.
In larger deployments, bypass TAPs work alongside network packet brokers to create a complete visibility and security architecture. The packet broker aggregates traffic from multiple TAPs and SPAN ports, then distributes specific traffic streams to the appropriate monitoring tools. Bypass TAPs handle the inline protection layer, while the packet broker manages the out-of-band monitoring layer.
Not all bypass TAPs offer the same capabilities. When evaluating options for your environment, several features have a meaningful impact on how well the product performs.
The ability to configure heartbeat intervals and thresholds lets you balance responsiveness against false positives. Faster heartbeat intervals detect failures more quickly but may trigger unnecessary failovers during brief processing delays. Look for solutions that let you tune these parameters to match your environment.
Your bypass TAP must match the speed and interface type of your network link. Common requirements include:
Fail-to-wire means traffic passes through the TAP directly if the device loses power or fails, keeping the network running without the security appliance. Fail-to-block means traffic stops if the TAP fails, which is appropriate in environments where dropping traffic is safer than allowing uninspected packets through. Understanding which behavior you need is essential before deployment.
Redundant, hot-swappable power supplies prevent the bypass TAP itself from becoming a single point of failure. If one power supply fails, the second maintains operation without interruption.
Some bypass TAP solutions include integrated packet processing capabilities that go beyond simple bypass switching. These features can include:
One of the most practical applications for bypass TAP technology is planned maintenance. Upgrading firmware, changing configurations, or replacing hardware on an inline security appliance typically requires taking it offline, which means either scheduling a maintenance window and accepting the network outage or leaving the appliance running and skipping the maintenance.
With a bypass TAP in place, you can take an inline appliance offline for maintenance without causing a network outage. When you disconnect the appliance or initiate a controlled shutdown, the bypass TAP detects the loss of heartbeat and activates the bypass relay. Traffic continues flowing through the direct path while you perform the maintenance work.
Once the appliance is back online and passing heartbeat packets, the TAP restores the inline traffic path automatically. Your team performs the work, the network keeps running, and users experience no interruption.
Bypass TAPs also simplify testing new inline security tools. You can connect a new appliance to the bypass TAP alongside your existing tool, test its configuration and behavior with live traffic, and then cut over to the new device when you're confident in its performance. The bypass TAP's failover capability provides a safety net throughout the testing process.
Organizations that operate networks where both security and uptime are non-negotiable depend on bypass TAPs to manage the tension between the two.
Financial institutions must meet strict regulatory requirements for network security while maintaining the continuous availability their transaction processing systems demand. An inline IPS that takes down payment processing, even briefly, creates immediate financial and regulatory consequences.
Hospital networks carry electronic health records, medical device communications, and clinical applications across the same infrastructure. Network outages affect patient care. Bypass TAPs allow inline security tools to protect these sensitive systems without creating availability risks.
Carrier and service provider networks are built on the assumption of continuous operation. Inline security tools protecting core infrastructure must never become the cause of the outages they're designed to prevent.
Government networks running classified workloads or critical national infrastructure require both rigorous security controls and uninterrupted operation. Bypass TAPs protect the inline tools that enforce access policies without introducing their own availability risks.
Understanding how bypass TAPs work is straightforward. Deploying them correctly requires attention to several details that are easy to overlook.
A bypass TAP must match the speed of both the network link it's protecting and the inline appliance connected to it. Speed mismatches cause traffic loss or prevent the bypass TAP from functioning at all.
Choosing fail-to-wire when your security policy requires fail-to-block, or vice versa, can create a serious security or availability problem. Confirm the appropriate failover behavior for each deployment before installation.
A bypass TAP with a single power supply is itself a potential point of failure. For critical links, always deploy bypass TAPs with dual hot-swappable power supplies.
Default heartbeat settings work well in typical environments, but may need adjustment for high-latency links, processing-intensive appliances, or environments with strict failover time requirements. Test your heartbeat configuration under realistic load conditions before relying on it in production.
The terms bypass TAP and bypass switch refer to the same type of device. Both describe hardware that sits inline on a network link, monitors the health of a connected security appliance using heartbeat signals, and automatically reroutes traffic if that appliance fails. Network Critical uses both terms to describe the same category of product.
Yes, modular bypass TAP platforms can protect multiple inline appliances simultaneously. Each bypass module in the chassis manages one inline appliance independently, so a failure on one link doesn't affect the others. This is particularly useful in environments with multiple inline tools protecting different network segments.
A well-designed bypass TAP adds negligible latency in normal operating mode. The bypass relay itself introduces microseconds of additional delay, which is imperceptible to network users and applications. The far greater latency concern is the inline security appliance itself, which the bypass TAP enables you to deploy safely.
Yes. A bypass TAP operates at the physical layer and doesn't need to inspect packet contents to perform its function. It passes all traffic through to the connected appliance, which handles any decryption requirements. The bypass TAP's heartbeat mechanism works independently of traffic content.
Network Critical has provided network visibility solutions to enterprises worldwide since 1997, helping organizations protect their inline security investments without compromising network availability. Our bypass TAP solutions combine automatic failover with the advanced packet processing capabilities your security architecture needs.
The SmartNA-XL delivers bypass TAP functionality alongside full TAP and packet broker capabilities in a scalable 1RU chassis. V-Line bypass modules support 1G, 10G, and 40G connections across both copper and fiber interfaces, with heartbeat monitoring that detects appliance failures in milliseconds. Dual hot-swappable power supplies ensure the SmartNA-XL itself never becomes a single point of failure, and PacketPro™ technology adds advanced filtering, slicing, header stripping, and payload masking for tools that need clean, targeted traffic.
Whether you're protecting a single inline IPS at your network edge or building resilient inline security across a distributed enterprise, our team can help you design an architecture that keeps your security tools effective and your network continuously available. Contact us to discuss your requirements, or explore our full range of bypass TAP solutions to find the right fit for your environment.