Modern organizations rely heavily on Intrusion Prevention Systems (IPS) to inspect network traffic, detect malicious activities, and block cyberattacks before they reach critical systems. However, one important concept that many network administrators encounter—especially in enterprise data centers, ISPs, banks, and large corporate environments—is IPS Shunting.

Although the term is not commonly discussed in beginner cybersecurity courses, IPS shunting is an important mechanism used to temporarily or permanently bypass an IPS device under certain conditions without interrupting network connectivity.

This article explains IPS shunting in detail, including its working principle, benefits, risks, deployment scenarios, fail-open mechanisms, high availability designs, troubleshooting, and best practices.

What is IPS Shunting?

IPS Shunting is the process of diverting (bypassing) network traffic around an Intrusion Prevention System instead of sending traffic through it for inspection.

In simple words:

Instead of:

Internet
    │
Firewall
    │
IPS
    │
Core Switch
    │
Servers

Traffic is temporarily redirected to:

Internet
    │
Firewall
    │
Core Switch
    │
Servers

The IPS remains connected but traffic no longer passes through it.

This process is known as shunting, traffic bypass, or IPS bypass.

Why is IPS Shunting Needed?

An IPS works inline.

Every packet passes through it.

If the IPS:

• crashes
• becomes overloaded
• loses power
• is under maintenance
• receives firmware upgrades

the entire network may become unavailable.

IPS shunting avoids this situation.

Main Purpose of IPS Shunting

The primary objectives include:

• Prevent network downtime
• Maintain business continuity
• Allow IPS maintenance
• Upgrade firmware safely
• Replace faulty IPS hardware
• Avoid packet loss during overload
• Ensure uninterrupted production traffic

Understanding Inline IPS

Normally traffic flows as:

Internet
      │
      ▼
+-------------+
| Firewall    |
+-------------+
      │
      ▼
+-------------+
| IPS         |
+-------------+
      │
      ▼
Core Network

Every packet is inspected.

If malicious:

Blocked

If legitimate:

Allowed

What Happens During Shunting?

Traffic is redirected.

Internet
      │
      ▼
Firewall
      │
      ├──────────────► Core Network
      │
     IPS

Traffic bypasses inspection.

Network remains operational.

IPS Shunting vs IPS Failure

These are completely different.

Types of IPS Shunting

1. Manual Shunting

Administrator manually bypasses IPS.

Used during:

• Maintenance
• Hardware replacement
• Firmware upgrades
• Network redesign

2. Automatic Shunting

Occurs automatically when:

• CPU reaches critical level
• Memory exhaustion
• Link failure
• Heartbeat failure
• IPS process crash

Traffic automatically bypasses IPS.

3. Hardware Bypass Shunting

Dedicated bypass switches detect:

• Power loss
• Hardware failure
• Link failure

They immediately connect incoming and outgoing links directly.

No manual intervention required.

4. Software-Controlled Shunting

Some enterprise IPS appliances dynamically modify routing or policies to bypass inspection.

Often integrated with:

• SDN
• Network controllers
• High Availability clusters

IPS Fail-Open vs Fail-Close

This is the most important concept.

Fail-Open

If IPS fails:

Traffic continues.

IPS Failure
       │
       ▼
Traffic Bypassed

Advantages:

• Zero downtime
• Business continuity
• Production remains online

Disadvantages:

• Traffic not inspected

Fail-Close

If IPS fails:

Traffic stops.

IPS Failure
      │
      ▼
Traffic Blocked

Advantages:

• Maximum security

Disadvantages:

• Complete network outage

Which Mode is Better?

Depends on organization.

IPS Shunting During Maintenance

Example:

Administrator upgrades IPS firmware.

Without shunting:

Users lose connectivity.

With shunting:

Traffic bypasses IPS.

Upgrade completes.

Traffic restored through IPS.

Users never notice downtime.

Shunting During Hardware Replacement

Old IPS removed.

Traffic redirected.

New IPS installed.

Traffic switched back.

No outage.

Load-Based Shunting

Some IPS appliances monitor:

• CPU usage
• Memory usage
• Session count
• Packet rate

When thresholds exceed limits:

Traffic bypasses inspection.

Example:

CPU = 98%

↓

Traffic Shunted

↓

CPU Normal

↓

Traffic Restored

High Availability with IPS Shunting

Many enterprises deploy:

Firewall
      │
      ▼
Bypass Switch
   │        │
IPS-1    IPS-2

If IPS-1 fails:

Traffic automatically switches.

No interruption.

Hardware Bypass Switch

A bypass switch continuously monitors IPS health.

If healthy:

Traffic → IPS

If unhealthy:

Traffic → Direct Link

Switching happens within milliseconds.

Packet Flow During Shunting

Normal:

Internet
 ↓
Firewall
 ↓
IPS
 ↓
LAN

Shunted:

Internet
 ↓
Firewall
 ↓
LAN

Advantages of IPS Shunting

Zero Network Downtime

Business operations continue.

Maintenance Without Outage

Firmware updates become easier.

Improved Availability

Mission-critical applications remain online.

Easier Hardware Replacement

No emergency downtime.

Disaster Recovery

Quick recovery from IPS failure.

Disadvantages

Traffic is no longer inspected.

Possible consequences:

• Malware passes
• Exploits succeed
• Attacks undetected
• Reduced visibility
• Compliance concerns

Security Risks

While shunted:

• Ransomware traffic may pass
• Exploit kits not blocked
• Botnet communication undetected
• Malicious downloads allowed

Therefore shunting should remain temporary whenever possible.

IPS Shunting in Large Enterprises

Common in:

• Banks
• Telecom providers
• Government networks
• Data centers
• Cloud providers
• Hospitals
• Manufacturing companies

Vendor Implementations

Many security vendors support IPS bypass mechanisms, including:

• Palo Alto Networks
• Fortinet
• Cisco Secure IPS
• Check Point
• Trellix
• Trend Micro
• Juniper
• Forcepoint

Implementation methods differ, but the objective remains the same.

Monitoring Shunting Events

Administrators should monitor:

• IPS health
• CPU utilization
• Memory utilization
• Interface status
• Heartbeat status
• Bypass switch logs
• Traffic volume
• Session count

Alerts should be generated immediately whenever shunting occurs.

Best Practices

• Enable monitoring and alerting
• Use hardware bypass switches where appropriate
• Test fail-open and fail-close behavior before production
• Keep IPS firmware updated
• Schedule maintenance windows
• Minimize shunting duration
• Maintain redundant IPS appliances
• Document all shunting events
• Review logs after restoration
• Conduct periodic disaster recovery testing

Common Troubleshooting Steps

If unexpected shunting occurs:

1. Check IPS power status.
2. Verify network interfaces.
3. Review CPU and memory usage.
4. Inspect bypass switch logs.
5. Confirm heartbeat communication.
6. Review firmware update status.
7. Check routing changes.
8. Verify high-availability synchronization.
9. Analyze network traffic spikes.
10. Restore inline inspection after resolving the issue.

Real-World Example

A manufacturing company operates 24×7 production systems.

During a scheduled IPS firmware upgrade:

• The bypass switch detects maintenance mode.
• Traffic is automatically shunted around the IPS.
• Production continues without interruption.
• The IPS is upgraded and rebooted.
• Health checks pass.
• Traffic is redirected back through the IPS.

Users experience no network outage while security inspection resumes immediately after maintenance.

Conclusion

IPS Shunting is a critical high-availability mechanism that enables organizations to maintain network connectivity when an Intrusion Prevention System is unavailable due to maintenance, upgrades, overload, or unexpected failures. While it helps eliminate downtime and ensures business continuity, it temporarily reduces security by allowing traffic to bypass inspection. Organizations should combine IPS shunting with redundancy, continuous monitoring, and clearly defined operational procedures to strike the right balance between availability and security.

Frequently Asked Questions (FAQ)

1. What is IPS shunting?

IPS shunting is the process of temporarily bypassing an Intrusion Prevention System so network traffic continues flowing without IPS inspection.

2. Why is IPS shunting used?

It is used to avoid network outages during maintenance, firmware upgrades, hardware failures, or excessive IPS load.

3. Does IPS shunting reduce security?

Yes. During shunting, traffic bypasses IPS inspection, increasing the risk that malicious traffic may pass undetected.

4. What is the difference between fail-open and fail-close?

Fail-open allows traffic to continue if the IPS fails, while fail-close blocks all traffic until the IPS is restored.

5. Is IPS shunting automatic?

It can be either manual or automatic, depending on the IPS, bypass hardware, and network design.

6. What devices support IPS shunting?

Many enterprise IPS and next-generation firewall solutions support bypass mechanisms, either through built-in features or external bypass switches.

7. Can IPS shunting occur during firmware upgrades?

Yes. Administrators often enable shunting during upgrades to prevent service interruptions.

8. Is IPS shunting the same as disabling the IPS?

Not necessarily. Shunting redirects traffic around the IPS, while disabling the IPS stops its inspection functions entirely.

9. How can organizations minimize the risks of shunting?

By keeping shunting periods short, using redundant IPS appliances, monitoring traffic closely, and restoring inline inspection promptly.

10. Is IPS shunting suitable for all organizations?

The decision depends on business requirements. Organizations prioritizing availability often use fail-open with shunting, while those prioritizing maximum security may choose fail-close designs.

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