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Zscaler: ZPA FQDN to IP Policy Evaluation Mechanics

Zscaler
06/25/2026
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Professional Services, Customer Success Division. And here I welcome you all to our new series, ZPA Unpacked, where we break down the power of ZPA. In the previous video, we introduced and learned about how ZPA's advanced FQDN to IP solution helps the customers. We looked at the overview of the solution. In this video, let's continue to understand more on how does the solution actually works, its mechanics. So let's dive in. How does the solution actually work? First and foremost, this advanced feature FQDN to IP policy evaluation is enabled at the individual customer's ZPA tenant environment. Once this solution is enabled and applied with segmentation accordingly, and a user attempts to access an application, there are two levels of checks introduced. The primary as standard, we still go ahead and check the FQDNs, the broader wildcard app segments, enforcing allow or block decisions. But this is where it changes the game. If the FQDNs are unknown, if the wildcards are too broad to segment, customers have the ability to apply a secondary level of policy rule base in their segmentation strategy. What ZPA does is, if the primary level access is allowed using FQDNs or wildcard domains, which may be broader, quite large in nature, ZPA will still go ahead and perform a secondary evaluation using the resolved IP address from the FQDN and wildcard domains, working with the DNS. Once the FQDN is resolved with an IP address, it gets matched against the IP or subnet based app segments that are also now present in the application segmentation rule based order to apply more granular access controls. This is where it changes the game altogether. The customers who do not have defined FQDN day one, they can still take their time and pace to identify, to structurize those elements, but bring in the IP based, the subnet based segmentation policies into ZPA and ZPA will then still continue to transition their journey towards zero trust mechanism. Controls by enforcing a secondary level of advanced check in combination with the primary level, as I explained, by checking the policies against the resolved IP addresses. Now note, this secondary mechanism, this secondary level of check is only triggered when the traffic from the first primary evaluation is allowed. If the traffic is blocked, naturally the secondary evaluation won't kick in, it won't trigger, right? Now to ensure the correct enforcement, the IP and subnet based policies must be placed above broader FQDN or wildcard domain based policies, or even if there are broader RFC1918 subnets defined by the customer, they must be placed lower in the rule base. So note that specific IP or specific subnet based policies must be placed above in the rule base than the FQDNs or broader wildcard domains or even wider RFC1918 IP address ranges. So let's take a look at this analogy, right? An easy way to think about this solution is an airport security style check. The first checkpoint verifies the identity and your travel destination, that being the FQDN, wildcard domain based check. And the secondary checkpoint where the traffic gets validated with additional checks, your security baggage, the boarding zone checks, right? That being the resolved IP based checks. Only when both checks pass, only then the access is allowed, ensuring stronger security and zero trust access. Hope that helped understanding using this analogy, the solution bit more. Now that you know how the solution works, coming up next, you'll see how customers are actually using this in real world. So don't miss the customer case study coming up in the next session. Stay tuned. Transcribed by https://otter.ai

TL;DR

  • ZPA's FQDN to IP policy evaluation implements a two-tier access control system: primary FQDN/wildcard domain checks followed by secondary IP-based validation when primary evaluation allows access
  • The secondary evaluation resolves FQDNs to IP addresses via DNS and matches them against IP or subnet-based app segments, enabling granular controls even when complete FQDN mapping is unavailable
  • Proper implementation requires placing specific IP/subnet policies above broader FQDN, wildcard domain, and RFC1918 policies in the rule base hierarchy
  • This dual-checkpoint approach allows organizations to enforce zero trust controls incrementally while structuring their FQDN inventory over time

Two-Level Policy Evaluation Framework

This technical walkthrough explains how Zscaler Private Access (ZPA) implements a dual-layer policy evaluation system for application access control. The primary level performs standard FQDN and wildcard domain checks to enforce initial allow or block decisions. When primary evaluation allows access but FQDNs are unknown or wildcards are too broad for precise segmentation, ZPA triggers a secondary evaluation layer. This advanced mechanism resolves the FQDN to its IP address via DNS, then matches that resolved IP against IP-based or subnet-based application segments configured in the policy rule base. This secondary check only activates when primary evaluation allows traffic, providing granular zero trust controls even in environments where complete FQDN mapping isn't available from day one.

Policy Ordering and Implementation Requirements

Proper policy enforcement requires specific rule base ordering. IP-based and subnet-based policies must be positioned above broader FQDN policies, wildcard domain policies, and RFC1918 subnet ranges in the segmentation rule base. This hierarchical structure ensures that more specific IP-level controls take precedence over broader domain-based rules. The feature is enabled at the individual tenant level and works in conjunction with DNS resolution to provide what Zscaler describes as an 'airport security style' dual-checkpoint approach—first verifying identity and destination (FQDN check), then validating with additional security controls (resolved IP check). This architecture allows organizations to transition toward zero trust incrementally while maintaining granular access controls during the migration process.

Chapters

0:00 - Introduction and Series Context
0:46 - How the Solution Works
1:17 - Primary and Secondary Evaluation Levels
3:42 - Policy Ordering Requirements
4:28 - Airport Security Analogy
5:13 - Next Steps and Preview

Key Quotes

1:25 "If the FQDNs are unknown, if the wildcards are too broad to Segment, customers have the ability to apply a secondary level of policy rule base in their segmentation strategy."
2:01 "ZPA will still go ahead and perform a secondary evaluation using the resolved IP address from the FQDN and wildcard domains, working with the DNS."
2:42 "The customers who do not have defined FQDN day one, they can still take their time and pace to identify, to structurize those elements, but bring in the IP based, the subnet based segmentation policies into ZPA."
4:56 "Only when both checks pass, only then the access is allowed, ensuring stronger security and zero trust access."

FAQ

What happens if the primary FQDN evaluation blocks traffic?

The secondary IP-based evaluation does not trigger if the primary FQDN check blocks traffic. The secondary layer only activates when the primary evaluation allows access, providing an additional granular control checkpoint for allowed traffic.

How should policies be ordered in the rule base for this feature to work correctly?

Specific IP-based and subnet-based policies must be placed above broader FQDN policies, wildcard domain policies, and RFC1918 subnet ranges in the segmentation rule base. This ensures more granular IP-level controls take precedence over broader domain-based rules.


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  • Zero Trust
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