Inline security tools sit directly in the path of live network traffic. Unlike out-of-band monitoring solutions that receive copies of traffic after it has already passed through the network, inline tools inspect every packet in real time and can act on what they find. An Intrusion Prevention System (IPS), for example, doesn't just detect suspicious traffic — it can block it instantly because the traffic flows through the tool before continuing to its destination.
That capability makes inline tools extremely powerful. It also creates a serious operational risk. If an inline security appliance fails, goes offline for maintenance, or becomes overwhelmed under heavy load, the consequence isn't simply a gap in your monitoring data. Traffic stops flowing entirely. Your network goes down.
Bypass TAPs — also called bypass switches — solve this problem. They sit between your network link and your inline security tools, continuously monitoring the health of those tools and automatically rerouting traffic if a failure is detected. Your security posture stays intact when tools are working normally, and your network stays online when they're not.
Inline security refers to any approach where security tools are physically inserted into a live network path, meaning traffic must pass through them to reach its destination. This gives those tools the ability to inspect, filter, block, or modify traffic in real time.
Out-of-band security tools receive a copy of network traffic — typically from a network TAP or a SPAN port — and analyze it passively. They can detect threats and generate alerts, but they cannot block malicious traffic because they only see a copy, not the original flow.
Inline tools work differently. Traffic physically enters the appliance, gets inspected, and then exits toward its destination. This gives inline tools three capabilities that out-of-band tools can never have:
Many of the most critical security tools in enterprise networks operate inline. Understanding which tools run inline helps clarify exactly what's at stake when they fail:
Each of these tools provides a function that is difficult or impossible to replicate in an out-of-band architecture. And each one, if it fails, can bring network traffic to a halt.
Placing any device in the path of live network traffic introduces a potential single point of failure. Most inline security appliances handle this through built-in fail-open or fail-closed mechanisms. Fail-open means that if the device loses power or crashes, traffic passes through unimpeded. Fail-closed means traffic stops completely.
Neither default behavior is ideal on its own.
A tool configured to fail-open keeps your network running during a failure, but it also leaves you without security coverage during an outage. If an IPS fails-open during an active attack, that attack proceeds unimpeded until the tool recovers. For organizations in regulated industries, a period of uninspected traffic may also represent a compliance violation.
A tool configured to fail-closed provides a safer security posture during failure, but the operational consequence is a complete network outage. Business-critical applications stop working. Transactions fail. Users lose connectivity. The reputational and financial cost of downtime quickly exceeds any short-term security benefit.
Even when tools are functioning correctly, they require regular updates, configuration changes, and hardware maintenance. Every planned maintenance window carries the same risk as an unplanned failure. Without a failover mechanism, teams face a difficult choice: take the network down during maintenance, or delay critical updates indefinitely.
The reality in most environments is that both outcomes cause harm. Delayed security updates leave known vulnerabilities unpatched, while unplanned network outages affect the business directly. Bypass TAPs eliminate this false choice.
A bypass TAP is a hardware device that sits between your network link and one or more inline security appliances. In normal operation, traffic flows from the network into the bypass TAP, out to the inline tool, back into the bypass TAP, and then continues to its destination. The bypass TAP acts as an intermediary that gives you control over what happens to traffic when the inline tool is unavailable.
Understanding the physical path helps clarify how bypass protection works:
This architecture means the bypass TAP is always in the path, but its role is transparent during normal operation. When everything is working, traffic moves through the inline tool as expected. The bypass TAP only changes the traffic path when it detects a problem.
When a bypass TAP enters bypass mode, it creates a direct electrical or optical connection between its two network-facing ports. Traffic moves through this connection without passing through the inline tool. The connection is made at the hardware level, which means it operates even if the bypass TAP itself loses power — a design characteristic sometimes called fail-safe operation.
This hardware-level bypass is what makes the technology reliable. Software-based failover mechanisms can fail along with the rest of a system during a crash. A hardware bypass relay operates independently of any software state, ensuring that traffic continues flowing even in the most severe failure scenarios.
The bypass TAP doesn't simply wait for an inline tool to disappear from the network before activating. It uses a technique called heartbeat monitoring to continuously verify that the inline tool is alive, responsive, and capable of processing traffic.
The bypass TAP generates small test packets — heartbeats — and sends them to the inline security appliance at regular intervals. These packets travel the same path as live traffic: into the tool's ingress port and back out through its egress port. When the bypass TAP receives the heartbeat packet back, it confirms three things:
If a predetermined number of consecutive heartbeat packets go unacknowledged, the bypass TAP concludes that the inline tool has failed or become unresponsive and switches traffic to the bypass path automatically.
A tool can appear powered on while being unable to pass traffic. Common scenarios include:
None of these scenarios would be detected by simply monitoring whether the appliance is powered on. Heartbeat monitoring catches all of them because it verifies end-to-end traffic traversal, not just power state.
Most bypass TAPs allow you to configure how quickly they respond to a failure by setting the heartbeat interval and the number of missed responses required to trigger bypass mode. A shorter interval with fewer missed packets means faster failover but higher sensitivity to brief, non-critical interruptions. A longer interval with more missed packets means slower failover but fewer false triggers. The right configuration depends on your environment's tolerance for both brief outages and brief security gaps.
Bypass TAPs typically operate in one of two main modes, and understanding the difference helps you choose the right configuration for each use case.
In inline mode, all live traffic flows through the inline security tool. The bypass TAP monitors the tool's health continuously via heartbeat and stands ready to reroute traffic if needed. This is the default operational state for any environment where the inline tool is functioning correctly.
Bypass mode can be triggered automatically by the heartbeat mechanism when a failure is detected, or manually by an administrator who needs to perform maintenance on the inline tool. In both cases, the result is the same: traffic flows directly between the two network-facing ports of the bypass TAP without passing through the inline appliance.
The key difference between automatic and manual bypass is intent. Automatic bypass is a failsafe response to an unexpected failure. Manual bypass is a planned operational action that allows your team to:
More advanced bypass TAP configurations support load balancing across multiple inline security appliances. Rather than directing all traffic to a single tool, the bypass TAP distributes traffic across a pool of appliances. If one tool in the pool fails, its traffic share is redistributed to the remaining healthy tools automatically.
This architecture is particularly valuable in high-traffic environments where a single inline appliance cannot handle the full line rate, or where organizations need to scale security capacity without changing their network topology.
Not all bypass TAPs are equal. When evaluating solutions, these are the capabilities that matter most for enterprise deployments:
Bypass TAPs are used wherever both network security and network availability are non-negotiable requirements. Several industries treat them as essential infrastructure rather than optional enhancements.
Trading platforms, payment processing systems, and banking applications cannot tolerate network outages. Even brief interruptions can result in failed transactions, regulatory reporting gaps, and significant financial losses. Inline security is mandatory in financial networks to meet regulatory requirements, but so is continuous uptime. Bypass TAPs bridge that gap.
Carrier networks and service providers deliver connectivity to millions of customers. Inline security tools in these environments must inspect traffic at extremely high speeds without introducing latency or creating availability risks. Bypass TAPs with high-speed support and hardware-level failover are standard components of telecom security architecture.
Government networks handle classified information and critical national infrastructure. Security tools in these environments cannot be optional, but they also cannot create single points of failure in systems that support essential services. Bypass TAPs provide the assurance that security coverage and network availability are not mutually exclusive.
Healthcare networks carry patient data and support clinical applications that directly affect patient safety. Regulatory requirements under frameworks such as Health Insurance Portability and Accountability Act (HIPAA) mandate security controls, while the clinical environment demands continuous availability for systems ranging from electronic health records to medical imaging. Bypass TAPs allow healthcare organizations to meet both requirements simultaneously.
It's worth understanding how bypass TAPs compare to alternative approaches to inline tool availability, since some organizations attempt to solve this problem with different methods.
Some organizations configure inline tools with dual Network Interface Cards (NICs) and rely on the tool's internal software to handle failover. This approach has a fundamental weakness: if the tool's software crashes, the failover mechanism crashes with it. A hardware bypass TAP operates at the physical layer, completely independently of the inline tool's software state.
Clustering multiple inline appliances for redundancy provides resilience, but it doesn't eliminate the need for bypass TAPs in every scenario. Cluster failover takes time, and during that transition window traffic may be dropped or uninspected. Bypass TAPs provide instantaneous hardware-level failover that complements, rather than replaces, higher-level redundancy architectures.
SPAN ports provide out-of-band visibility but cannot support inline security tools at all. A tool receiving traffic from a SPAN port has no ability to block or modify that traffic. Any organization replacing inline tools with SPAN-connected tools sacrifices the capability to prevent threats in real time, not just detect them.
The SmartNA-XL platform from Network Critical integrates bypass TAP functionality with advanced packet broker capabilities in a single modular 1RU chassis. This means your bypass protection, traffic aggregation, filtering, and tool distribution can all be managed from a single platform rather than requiring separate dedicated devices for each function.
The SmartNA-XL includes PacketPro technology, which allows you to apply filtering rules to traffic before it reaches your inline security tools. Rather than sending all traffic to every inline tool, you can direct specific traffic types to specific tools based on IP address, protocol, port, or other criteria. This reduces the processing load on each inline tool and can significantly extend the lifespan and effectiveness of your security infrastructure.
Configuration and monitoring of bypass TAPs, filtering rules, and traffic paths is handled through Drag-n-Vu, Network Critical's graphical management interface. Drag-n-Vu uses a visual drag-and-drop approach to creating traffic policies, which eliminates the risk of configuration errors that can occur with command-line-only management. It also integrates with Simple Network Management Protocol (SNMP)-based network management systems for centralized alerting when bypass mode is triggered.
The SmartNA-XL's modular architecture means you can add or replace TAP modules, including bypass modules, without powering down the chassis. This design extends the bypass TAP concept to the hardware itself: even the visibility infrastructure is designed for continuous operation without forced maintenance windows.
Yes, while a bypass TAP is in bypass mode, traffic is not passing through the inline security tool. This is a deliberate trade-off: network availability is maintained, but the inline tool's inspection capability is temporarily suspended. This is why bypass mode should be treated as a transient state. The goal of automatic failover is to keep the network running while the inline tool is recovered and returned to service as quickly as possible. For planned maintenance, some organizations use a secondary inline tool during the bypass period to maintain continuous coverage.
A well-designed bypass TAP should not be a single point of failure. Features that mitigate this risk include dual hot-swappable power supplies, fail-safe hardware bypass relays that operate without power, and management interfaces that are isolated from the data path. If the bypass TAP itself loses power, the hardware relay defaults to the bypass position, keeping traffic flowing even without any active electronics in the device.
Bypass TAPs are available across a wide range of network speeds. Network Critical's bypass solutions support 1G, 10G, and 40G links, with the modular SmartNA-XL chassis able to combine multiple speed configurations within a single platform. For organizations running 100G or higher speed links, it's important to confirm that the bypass TAP's hardware relay and internal switching fabric can handle the full line rate without packet loss.
A properly designed bypass TAP introduces negligible latency in normal inline operation. The device is engineered to forward traffic between its ports at wire speed without any software processing in the data path. The bypass relay and physical connections add only the propagation delay of the additional cable lengths involved, which is typically measured in nanoseconds and has no measurable impact on application performance.
Bypass TAPs operate at Layer 1 and Layer 2, which means they forward traffic regardless of whether it is encrypted. The inline security tool connected via the bypass TAP is responsible for any decryption and inspection of encrypted traffic. This means bypass TAPs are fully compatible with SSL/TLS inspection appliances and other inline tools that handle encrypted traffic.
Deploying inline security tools without bypass protection is a risk that most organizations can't afford to carry. Whether the consequence is a network outage during an unexpected failure or a forced choice between security coverage and maintenance access, the operational impact is real and preventable.
Network Critical has provided network visibility solutions to enterprises, carriers, and government organizations since 1997. Our bypass TAP solutions are designed to make inline security sustainable, giving your security team the confidence to deploy the tools they need without creating availability risks for the business.
The SmartNA-XL platform combines bypass TAP functionality with modular packet broker capabilities, supporting 1G, 10G, and 40G environments in a compact 1RU chassis. Advanced filtering through PacketPro technology, hot-swappable modules, dual redundant power supplies, and intuitive management via Drag-n-Vu make it the complete platform for organizations that need inline security without compromising network uptime.
Whether you're deploying inline security for the first time, adding bypass protection to an existing tool deployment, or planning a high-availability architecture across multiple sites, our team can help you design an approach that meets your security requirements and your availability requirements without sacrificing either.