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Network TAP 101

Post 1 : By suktech24, Thurs 9 Jan 2025, Estimated reading time : 5-7 mins

A Network TAP (Test Access Point) is a specialized hardware device used to monitor and capture network traffic by creating a passive copy of all data flowing between two points on a network. It enables comprehensive network visibility and is an essential component in modern network monitoring and security setups.

Network TAPs function by passively replicating the data passing through a network link and forwarding this duplicated traffic to monitoring or analysis tools, such as a Network-based Intrusion Prevention System (NIPS). Importantly, TAPs achieve this without interfering with the original traffic flow, ensuring network performance remains unaffected.

This blog post will delve into the following topics :

  1. How a Network TAP Works
  2. Advantages of Using a Network TAP
  3. Why Use a TAP for a Network-Based IPS?
  4. How Network TAP enables an Intrusion Prevention System (IPS) to get a copy of all traffic
  5. Alternative: Port Mirroring (SPAN – switched port analyzer)
  6. Use Case for TAPs in NIPS Deployment
  7. Decryption Methods for Analyzing Encrypted Network Traffic
  8. Limitations of TAPs with IPS
  9. Evolution from IDS/IPS to Network Detection and Response (NDR)
  10. Python Code

1. How a Network TAP Works

  1. Placement in the Network:
    • A TAP is typically installed between two network devices, such as a switch and a router, or at critical junctions in the network.
    • It intercepts the data on the link to create a copy of all packets.
  2. Traffic Duplication:
    • The TAP duplicates both directions of traffic (inbound and outbound) and sends the copies to a monitoring or analysis device (e.g., NIPS) while allowing the original traffic to pass through unaffected.
  3. Passive Monitoring:
    • A TAP is a passive device and does not modify or interact with the network traffic. This ensures that its operation does not introduce latency or affect the performance of the network.

2. Advantages of Using a Network TAP

  • Complete Traffic Visibility: Captures all network traffic, including packets that may not be visible using other methods (e.g., malformed packets).
  • Passive Operation: Does not affect network performance or introduce points of failure in the network.
  • Reliable Monitoring: Provides an exact copy of the traffic, ensuring no packets are missed during analysis.
  • Secure Design: Cannot be easily detected or tampered with, ensuring integrity and confidentiality of the monitoring process.

3. Why Use a TAP for a Network-Based IPS?

  • Accurate Detection: A NIPS requires complete traffic visibility to effectively detect and respond to threats. A TAP ensures no traffic is missed.
  • Out-of-Band Monitoring: By using a TAP, the IPS can monitor traffic without interfering with the live network, reducing the risk of introducing bottlenecks or failures.
  • Enhanced Security: TAPs allow the IPS to analyze traffic without being directly connected to the operational network, reducing the attack surface.

4. How Network TAP enables an Intrusion Prevention System (IPS) to get a copy of all traffic

How it Works:

  1. Passive Monitoring: Network taps are “passive” devices, meaning they don’t interfere with the normal flow of network traffic. They simply copy the data passing through the network segment.
  2. Three Ports: A typical network tap has three ports:
    • A-port: Connects to the first network device.
    • B-port: Connects to the second network device.
    • Monitor port: Connects to the IPS or other monitoring devices.
  3. Traffic Flow:
    • Network traffic flows between the A-port and B-port as usual.
    • The tap simultaneously copies all this traffic to the monitor port.

Benefits for IPS:

  • Complete Visibility: The IPS receives a copy of every packet traversing the network segment, ensuring no traffic goes undetected.
  • No Performance Impact: Since the tap is passive, it doesn’t introduce any latency or performance degradation on the primary network.
  • Reliable Monitoring: Network taps are designed for high reliability and can handle high-speed network traffic without dropping packets.

5. Alternative: Port Mirroring (SPAN – switched port analyzer)

A commonly compared alternative to a TAP is Port Mirroring (or SPAN – Switched Port Analyzer), where a network switch duplicates traffic from specific ports to the monitoring device. While less expensive and easier to configure, it has several drawbacks:

  • Performance Impact: SPAN can degrade the performance of the switch.
  • Incomplete Capture: May drop packets under high loads.
  • Risk of Overload: Mirrored traffic competes with regular traffic, potentially affecting accuracy.

6. Use Case for TAPs in NIPS Deployment

  • Scenario: You have a high-speed network with a critical need for zero-packet-loss monitoring.
  • Solution: Deploy an optical or aggregation TAP to feed full-duplex traffic to the NIPS, ensuring complete visibility and reliable detection of potential intrusions.

7. Decryption Methods for Analyzing Encrypted Network Traffic

While a Network TAP captures all data traversing the network, encrypted traffic remains unintelligible without decryption. This encrypted data appears as binary information that cannot be analyzed without the appropriate decryption methods. Analyzing encrypted network traffic is essential for detecting threats and ensuring compliance. However, encryption poses significant challenges for security tools like Network TAPs (Test Access Points) and Intrusion Prevention Systems (IPS), which require visibility into network data to function effectively. To address this, organizations can implement several decryption methods, each with its own advantages and limitations.

Note: Section 7 summarizes the article written by Ghufran Ashiq, https://www.linkedin.com/advice/1/what-best-way-decrypt-encrypted-traffic-analysis-8bi0e

7.1. Passive Decryption

Passive decryption involves capturing encrypted traffic without disrupting its flow. Tools such as network TAPs or switch port mirroring are used to duplicate network traffic, which is then decrypted using available encryption keys or certificates. This method is ideal for minimizing latency and maintaining network performance. However, it relies on the availability of encryption keys, which can be challenging to obtain, especially with advanced protocols like TLS 1.3 that encrypt more of the handshake process.

Advantages:

  • Non-intrusive, preserving network performance
  • Suitable for compliance monitoring and forensic analysis

Limitations:

  • Ineffective against certain encryption protocols
  • Requires access to encryption keys or certificates

7.2. Active Decryption

Active decryption intercepts and decrypts traffic in real-time before it reaches its destination. This is typically achieved using network proxies or specialized security appliances that act as intermediaries. The system generates and manages encryption keys, often through internal Certificate Authorities (CA) or self-signed certificates. While active decryption offers deeper inspection capabilities, it can introduce latency and potential security risks.

Advantages:

  • Enables comprehensive traffic analysis
  • Supports advanced security policies and threat detection

Limitations:

  • May increase latency and impact user experience
  • Requires careful key management and certificate handling

7.3. Endpoint-Based Decryption

This method decrypts traffic directly at the source or destination endpoint using installed agents or drivers. These tools intercept and decrypt traffic before it is transmitted over the network. Endpoint-based decryption is particularly effective for analyzing encrypted data generated by applications beyond the network administrator’s control. However, it may consume endpoint resources and requires user consent for deployment.

Advantages:

  • Direct access to decrypted traffic
  • Effective for application-specific encryption

Limitations:

  • Potential performance impact on endpoints
  • Requires deployment and maintenance of endpoint agents

7.4. Hybrid Decryption

Hybrid decryption combines passive, active, and endpoint-based methods to create a comprehensive decryption strategy. This approach provides flexibility in managing diverse encryption protocols and traffic sources. Hybrid solutions often involve integrating multiple tools and systems, which can increase complexity and operational costs but offer more robust visibility and threat detection capabilities.

Advantages:

  • Flexible and adaptable to various encryption types
  • Enhanced security coverage across network segments

Limitations:

  • Higher complexity and maintenance overhead
  • Potential for increased costs

8. Limitations of TAPs with IPS

Using a TAP with an IPS can limit the IPS to a detection-only role (similar to an IDS). Because the TAP provides a copy of the traffic, the IPS cannot block malicious traffic in real-time. Inline deployment is required for prevention, but many organizations avoid this due to the risk of false positives impacting critical traffic.

While network TAPs (Test Access Points) provide a reliable method for monitoring network traffic, their integration with Intrusion Prevention Systems (IPS) introduces certain limitations. One significant drawback is that using a TAP forces the IPS into an Intrusion Detection System (IDS) role. In this configuration, the IPS can only monitor and alert on malicious activity but cannot actively block or prevent threats. This setup diminishes the proactive security capabilities that an IPS is designed to offer.

For an IPS to effectively prevent threats, it must be deployed inline, allowing it to analyze and potentially block malicious traffic in real time. However, many organizations hesitate to enable the blocking feature of IPS due to concerns about disrupting legitimate network operations. This caution is justified given the high false positive rates often associated with IDS/IPS solutions, which can inadvertently halt critical business functions.

9. Evolution from IDS/IPS to Network Detection and Response (NDR)

Traditional IDS solutions have struggled with high false positives and noise, leading to a decline in their usage within Security Operations Centers (SOCs). In response, Network Detection and Response (NDR) solutions have emerged as more intelligent alternatives. NDR systems leverage advanced AI and machine learning to analyze network traffic, including encrypted data, providing deep insights into potential threats with minimal false alarms.

FortiNDR, for example, offers agentless visibility, AI-powered threat detection, and seamless integration with various security tools. Designed for both cloud and air-gapped environments, it ensures effective response across IT, OT, and IoT networks, with features like automated investigations and orchestrated incident response, significantly enhancing SOC efficiency.

The Gartner page on Network Detection and Response (NDR) provides insights into top NDR solutions like Darktrace, Vectra AI, ExtraHop, and Cisco Secure Network Analytics, highlighting their strengths in detecting abnormal behaviors and applying automated responses to network traffic data. These products combine behavioral analytics, machine learning, and AI to improve threat detection while reducing false positives, ensuring better security and response efficiency. For further details, you can explore the full Gartner reviews here.

10. Python code

python network_tap_1.py 

class NetworkTap:
    """
    Simulates a network tap that passively copies network traffic
    """
    
    def __init__(self, a_port, b_port, monitor_port):
        """
    
        """
        self.a_port = a_port
        self.b_port = b_port
        self.monitor_port = monitor_port
    
    def tap_traffic(self, traffic):
        return traffic.copy()
    
class IntrusionPreventionSystem:
    """
    Simulates an Intrusion Prevention System that analyzes network traffic
    """
    def analyze_traffic(self, traffic):
        intrusions = []
        for packet in traffic:
            if "malicious" in packet.lower():
                intrusions.append(packet)
        return intrusions
    

def run_network_monitoring():
    """
    Runs the network monitoring simulation with IPS anlysis
    """
    network_traffic_sample = [
        "Data packet 1", 
        "Data packet 2",
        "Malicious packet 1",
        "Data packet 3",
        "Malicious packet 2"
    ]
    
    network_tap = NetworkTap("A", "B", "Monitor")
    
    network_traffic_copy_to_monitored_port = network_tap.tap_traffic(network_traffic_sample)
    
    ips = IntrusionPreventionSystem()
    intrusions_detected = ips.analyze_traffic(network_traffic_copy_to_monitored_port)
    
    if intrusions_detected:
        print("Detected intrusions:")
        for intrusion in intrusions_detected:
            print(intrusion)
    else:
        print("No intrusion detected.")
    
if __name__ == "__main__":
    run_network_monitoring()

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