Which FTD Mode Survives Any Failure at the Perimeter?
An engineer must deploy a Cisco Secure Firewall Threat Defense instance. The company wants the Secure Firewall Threat Defense deployment to allow business traffic in the event of any type of failure, and there must be no connectivity issues caused by the IPS in the perimeter of its data center. Which implementation mode must the engineer use?
Community Votes
60% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The question tests failure-resilience modes for an inline FTD deployment, and the trap is confusing Snort fail open (software-only) or passive monitoring (no inline enforcement) with hardware bypass, which covers power and hardware faults.
Cisco Secure Firewall Threat Defense hardware bypass keeps an inline interface pair passing traffic during power, software, or hardware failure. This page explains why hardware bypass (A) is the correct answer when the IPS at the data center perimeter must survive any type of failure.
Many candidates pick passive mode (D) because it avoids inline connectivity risk entirely, but passive mode receives a traffic copy via SPAN/RSPAN/ERSPAN and cannot provide inline intrusion prevention, so it does not meet the requirement for an IPS in the perimeter.
Community Discussion (3 comments)
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Expert Analysis
Why the Answer Is Correct
Hardware bypass (A) is the only option that keeps an inline Secure Firewall Threat Defense interface pair passing business traffic through a power outage or hardware failure, not just a software fault. Cisco documents that on supported modules, the hardware bypass feature ensures traffic continues to flow between an inline pair and can "maintain network connectivity in the case of software or hardware failures," as whysohardwhy quoted. The question's phrase "any type of failure" is the decisive clue: it rules out software-only mechanisms and points to a physical-layer bypass. Because the FTD sits in the perimeter as an IPS, hardware bypass preserves the inline path while still allowing inspection when the device is healthy. This matches the requirement to avoid connectivity issues caused by the IPS during any failure.Why the Other Options Are Wrong
Snort fail open (B) only lets packets pass when the Snort inspection engine fails; it does not address a power supply, module, or full appliance failure, so it fails the "any type of failure" test. An inline set (C) is simply the deployment placement that makes inspection possible, but by itself it does not provide a bypass path and can drop traffic if the FTD fails. Passive mode (D) does eliminate inline connectivity risk because it receives a copy of traffic via SPAN, RSPAN, or ERSPAN, but it also removes the ability to block malicious traffic inline, which conflicts with placing an IPS in the perimeter. Andy0724 argued for passive to "avoid both hardware failure and Snort engine failure as well," yet that choice changes the deployment from prevention to monitoring and does not satisfy the question's inline IPS premise. Thus A is the only option that preserves business traffic across all failure types while keeping enforcement in the path.Community Comment Notes
The community split 60 votes for A and 40 for D, showing that passive mode is an attractive distractor. Andy0724 reasoned that passive mode can "avoid both hardware failure and Snort engine failure as well," which is true for connectivity but ignores the loss of inline prevention. whysohardwhy supplied the Cisco wording that hardware bypass can "maintain network connectivity in the case of software or hardware failures" and observed that "any type of failure" is the hint. That documentation quote directly supports selecting hardware bypass over Snort fail open. The documented feature and the failure scope therefore align with option A.Official Reference
Exam Strategy
When a question stresses "any type of failure" or power outage, prefer hardware bypass over Snort fail-open, which only covers software faults. Map each option to the failure layer it protects: software (fail open), hardware/power (hardware bypass), and monitoring-only (passive).
Frequently Asked Questions
Why is Snort fail open not enough for "any type of failure"?
Snort fail open only passes traffic when the Snort process fails; it does not protect against power loss or hardware failure, which hardware bypass is designed to cover.
Can passive mode meet the no-connectivity-issues requirement?
Passive mode avoids inline failure by receiving a SPAN, RSPAN, or ERSPAN copy, but it cannot block traffic inline, so it does not satisfy the IPS-at-the-perimeter premise.
Which FTD platforms support hardware bypass?
Cisco documents hardware bypass for certain interface modules on Firepower 9300, 4100, and 2100 series appliances, so verify platform support before relying on it.