Full packet capture is exactly what it sounds like: recording every single packet that crosses your network, in its entirety, without sampling, gaps, or dropped frames. Security teams rely on it for incident investigation. Compliance teams depend on it for audit trails. Network engineers use it to diagnose performance problems that disappear before anyone can identify them. But full packet capture is only as good as the traffic access layer beneath it, and that's where most organizations quietly fail.
The problem isn't your capture tool. It's how traffic gets to that tool. When you rely on switch port analyzer (SPAN) ports to feed packet capture appliances, you're building a high-stakes monitoring capability on infrastructure that was never designed for it. SPAN ports drop packets under load, introduce timing artifacts, and miss traffic entirely during hardware stress events. For true full packet capture, you need purpose-built network TAPs at the access layer, combined with network packet brokers to manage and deliver that traffic intelligently.
This article explains why TAP infrastructure is the foundation of reliable full packet capture, how it works technically, and what you need to consider when designing a visibility architecture that won't let you down when it matters most.
Packet capture sits at the intersection of network security, performance management, and compliance. Understanding why each discipline depends on it helps clarify why incomplete capture is never an acceptable trade-off.
When a security incident occurs, your forensic investigation depends on having a complete record of what happened. Partial captures leave gaps that attackers can exploit in the narrative, and those gaps can mean the difference between understanding a breach fully and missing lateral movement or data exfiltration paths entirely.
Full packet capture lets security teams:
Without complete packet data, incident response becomes an exercise in educated guessing rather than evidence-based analysis.
Many performance problems are intermittent. They occur at specific times, under specific load conditions, or between specific application tiers, and they disappear before anyone can capture useful diagnostic data. Full packet capture creates a continuous record that lets you go back and examine exactly what was happening on the wire during a performance event.
Industries including financial services, healthcare, telecommunications, and government operate under frameworks that require traffic recording for defined retention periods. Full packet capture provides the raw evidence that supports compliance attestation, and TAP-based infrastructure provides the reliability guarantees that sampling approaches simply can't deliver.
SPAN ports are a standard feature on managed switches, and for lightweight monitoring tasks they're perfectly adequate. But for full packet capture in production environments, their architectural limitations create real problems.
When a switch's CPU and forwarding engine come under load, SPAN port mirroring is one of the first functions that gets deprioritized. The switch's primary job is forwarding production traffic, and if it has to choose between dropping a mirrored monitoring copy or affecting a production packet, the monitoring copy loses every time.
This creates a fundamental reliability problem: SPAN ports drop packets most frequently during the high-traffic events that are most likely to be significant from a security or performance perspective. You're most likely to lose capture data precisely when you need it most.
SPAN ports can introduce inconsistent timing between packets because the mirroring process doesn't always preserve the precise inter-packet gaps present in the original traffic. For protocol analysis and certain performance diagnostics, this timing distortion produces misleading results.
Most switches support a limited number of simultaneous SPAN sessions. In environments where multiple monitoring tools need access to the same traffic, SPAN ports quickly become a bottleneck. You end up with contention between monitoring and security tools, forcing trade-offs about which tools get visibility at any given time.
Common SPAN port limitations include:
A network test access point (TAP) takes a fundamentally different approach to traffic access. Instead of asking the switch to create a software copy of traffic, a TAP sits inline on the physical link and creates a hardware-level copy at the physical layer. The production traffic path doesn't depend on the TAP's monitoring function in any way.
Passive fiber TAPs work by splitting the optical signal on a fiber link. When light travels through the fiber, the TAP uses optical splitter technology to divert a percentage of that light to monitoring ports, with the remainder continuing down the production link. Because this splitting occurs at the physical layer, it requires no power, introduces no processing delay, and cannot fail in a way that affects the production circuit.
This "always-on" characteristic is particularly valuable for full packet capture:
Ethernet TAPs serve copper network segments where passive optical splitting isn't possible. An active Ethernet TAP sits inline on the copper link and regenerates the signal, creating independent monitoring copies of both the transmit and receive streams. The monitoring output presents both streams simultaneously to capture tools, preserving the full-duplex nature of the traffic.
Active TAPs include fail-safe circuitry that ensures the production link continues even if the TAP loses power. This fail-safe behavior is critical in environments where monitoring infrastructure can't be allowed to affect network availability.
| Characteristic | Network TAP | SPAN Port |
|---|---|---|
|
Packet loss under load |
None |
Common |
| Error frame capture | Yes | Often filtered |
| Production traffic impact | Zero | CPU overhead |
| Simultaneous tool access | Multiple via aggregation | Limited sessions |
| Timing accuracy | Wire-accurate | Can be distorted |
| Failure impact on network | None (fail-safe) | N/A |
TAPs solve the access problem. But in any real-world network with multiple links and multiple monitoring tools, TAPs alone create a different challenge: you end up with traffic streams from dozens of TAP deployments, and no efficient way to get the right traffic to the right tools.
This is where network packet brokers become essential. A packet broker sits between your TAPs and your monitoring tools, aggregating traffic from multiple sources, applying filtering and processing rules, and distributing the resulting streams to appropriate tools.
In a typical data center, you might have TAPs deployed across core uplinks, server access links, internet edge connections, and inter-segment boundaries. Each TAP generates its own monitoring copy of the traffic on its specific link. Without aggregation, each monitoring tool would need a direct connection to every TAP, creating an unmanageable connection matrix.
A packet broker aggregates all of those streams into a single platform, then distributes filtered subsets to each tool based on configured policies. A forensic capture appliance can receive everything. An intrusion detection system can receive only external-facing traffic. A VoIP analyzer can receive only traffic on relevant ports.
Full packet capture at scale generates enormous data volumes. Unfiltered capture of a 10Gbps link running at moderate utilization can produce hundreds of terabytes per day. Packet brokers let you apply intelligent filtering before traffic reaches capture storage, reducing volume while ensuring you retain everything that matters.
Filtering capabilities that support full packet capture workflows include:
Beyond aggregation and filtering, packet brokers provide processing capabilities that make captured data more useful and easier to work with:
Building a capture architecture that reliably delivers complete packet data requires thinking about each layer: physical access, aggregation, filtering, and storage. Getting any layer wrong introduces the gaps you're trying to eliminate.
Start by identifying which network links must be captured for your security, compliance, and operational requirements. Not every link in the network needs full capture; prioritize based on risk and regulatory requirements.
Different link types require different TAP solutions:
Connect your TAP monitoring outputs to a packet broker that provides sufficient port density and processing capacity for your capture volume. Key selection criteria include:
Work with your security and compliance teams to define exactly what traffic must be captured and retained. Configure packet broker filtering policies to deliver the required traffic to capture storage while routing other traffic streams to appropriate monitoring tools.
Before relying on your capture infrastructure for security operations or compliance, validate that it's actually capturing what you expect. Generate known traffic patterns across each tapped link and verify that they appear in your capture files with accurate timestamps and complete payloads.
Full packet capture often coexists with inline security tools like next-generation firewalls, intrusion prevention systems, and SSL inspection appliances. These tools sit in the traffic path and process every packet in real time, which means their failure can affect network availability.
Bypass TAPs protect inline security tools by monitoring their health and automatically redirecting traffic around a failed appliance. The TAP sends continuous heartbeat signals through the inline tool; if those signals stop being returned, the TAP closes the bypass relay and routes traffic directly, maintaining network availability while the tool is repaired or restarted.
In environments where both full packet capture and inline security tools are deployed, bypass TAPs provide several benefits beyond simple failover:
As capture deployments grow across multiple sites and dozens of TAP points, operational management becomes a significant concern. Misconfiguration of TAP or packet broker infrastructure can create silent monitoring gaps, where you believe you're capturing traffic but aren't.
The Drag-n-Vu management platform provides a graphical interface for configuring and managing Network Critical TAP and packet broker infrastructure. Its visual traffic mapping approach reduces configuration errors by making the relationship between network links, TAP points, packet broker ports, and monitoring tools immediately visible.
Key management capabilities that support full packet capture operations include:
Maintain clear documentation of exactly which links are tapped, which TAP feeds are aggregated into which packet broker inputs, and which filtering policies determine what reaches your capture storage. Without this documentation, diagnosing gaps in capture data becomes extremely difficult, particularly under the time pressure of an active security incident.
Even organizations that have invested in TAP infrastructure sometimes find that their capture coverage has holes. Understanding the common failure modes helps you avoid them.
A full-duplex link carries traffic in both directions simultaneously. Capturing only one direction of a link means missing half the conversation. Proper TAP deployment captures both transmit and receive streams and presents them to monitoring tools with appropriate stream identification.
If the total traffic volume across all TAP feeds exceeds the packet broker's processing capacity, packets will be dropped at the broker rather than the TAP. This is particularly dangerous because it creates the illusion of complete coverage while silently losing data. Always provision packet broker capacity with headroom for peak traffic events.
As networks grow and change, new links get added and existing links get upgraded. If your TAP deployment process doesn't include a step to assess and address monitoring requirements for new infrastructure, coverage gaps accumulate over time.
Encrypted traffic can only be captured in unencrypted form at specific points: either before encryption or after decryption. If your TAPs are positioned outside your SSL inspection infrastructure, you're capturing encrypted payloads that are of limited value for security analysis. Ensure your capture points align with where traffic is visible in plaintext.
Flow data (NetFlow, IPFIX, sFlow) records metadata about network connections, including source and destination addresses, ports, protocols, and byte counts, but doesn't capture actual packet payloads. Full packet capture records the entire packet, including all headers and payload data. Flow data is useful for traffic analysis and anomaly detection but can't support forensic investigation or content inspection. Full packet capture supports both use cases.
Storage requirements depend heavily on traffic volumes, retention periods, and whether you're applying filtering or payload truncation. A 1Gbps link at 50% utilization generates roughly 5-6TB of uncompressed capture data per day. Packet slicing, compression, and filtering can reduce this significantly. Most organizations capture full payloads for short retention periods (days to weeks) and retain header-only data for longer periods.
Yes, but only if your capture points are positioned correctly. TAPs deployed on links where traffic is unencrypted, either before encryption at the source or after decryption at an SSL inspection appliance, will capture readable payloads. TAPs deployed outside the encryption boundary capture encrypted payloads, which may still have value for metadata analysis and flow reconstruction but won't support payload content inspection.
Passive fiber TAPs introduce zero latency and have no impact on network performance because the optical splitting process is a physical phenomenon with no processing delay. Active Ethernet TAPs introduce latency measured in nanoseconds, which is negligible for all practical purposes. Neither TAP type consumes switch CPU or forwarding capacity, unlike SPAN ports.
Network Critical's TAP range supports network speeds from 10/100/1000Mbps through 10G, 25G, 40G, 100G, and up to 400Gbps with the SmartNA-PortPlus HyperCore, ensuring your visibility infrastructure can keep pace with network upgrades.
Full packet capture is only reliable when the underlying access infrastructure is designed for the job. Network Critical has been delivering purpose-built network visibility solutions since 1997, with TAP and packet broker technology deployed in some of the most demanding security and compliance environments in financial services, defense, healthcare, and telecommunications.
Our network TAPs provide guaranteed, lossless packet capture across speeds from 1Gbps to 400Gbps. Passive fiber options deliver zero-power, zero-latency access to optical links, while active Ethernet TAPs with Fastfail technology protect copper segments without affecting network availability. Ninety percent of high-compliance organizations choose TAPs over SPAN ports precisely because of this reliability guarantee.
The SmartNA-PortPlus and SmartNA-XL packet broker platforms aggregate traffic from multiple TAP points, apply intelligent filtering and deduplication, and deliver precisely the right traffic streams to your capture and monitoring tools. Whether you're instrumenting a single data center or building consistent capture coverage across a distributed enterprise, our team can help you design an architecture that provides complete, verifiable packet capture without gaps.