FortiGate 200F Shared Interface Policy Conflict during Inter-VDOM Routing
Source NAT (SNAT) and active user authentication policies sharing hardware-accelerated NPU inter-VDOM links collide inside the kernel iprope compiler, corrupting port-translation tuples and dropping inter-tenant transit sessions.
Technical Root Cause Analysis
On mid-range enterprise appliances such as the FortiGate 200F, 201F, and 400F, hardware NP6Lite/NP6xLite network processors accelerate inter-VDOM communications using virtual NPU links (npu0_vlink0 and npu0_vlink1).
In FortiOS 7.2.1 through 7.2.5, when multiple tenant VDOMs enforce Source NAT (SNAT) or user captive portal authentication rules on the same shared inter-VDOM transit interface, the Fortinet Configuration Compiler (fcnfg) fails to segregate translation hash tables across virtual domain namespaces.
When outbound traffic returns from the internet or shared services VDOM, the hardware IP rules property table (iprope) resolves identical port translation tuple IDs across different tenant contexts. The kernel detects an illegal state collision and silently discards the packet, generating repeated iprope match error log traces.
Affected Firmware & Blast Radius Matrix
| FortiOS Branch | Vulnerable Builds | Confirmed Clean Build | Status & Workaround |
|---|---|---|---|
| FortiOS 7.2 | 7.2.1 – 7.2.5 | 7.2.6+ | Segregate SNAT IP pools per VDOM |
| FortiOS 7.4 | 7.4.0 | 7.4.1+ | Namespace isolation enforced in iprope |
| FortiOS 7.0 | Not Affected | 7.0.x Branch Clean | Legacy iprope compiler used per-VDOM hashing |
Platform Impact: Confined to multi-VDOM deployments on FortiGate 200F, 201F, and 400F appliances running NPU-accelerated inter-VDOM links with overlapping SNAT or user authentication rules.
Step 01: Free Verification CLI (Safe Read-Only)
Execute these diagnostic commands to inspect iprope compiler state and identify conflicting inter-VDOM translation sessions:
Diagnostic Commands
# 1. Inspect compiled hardware iprope rule tables on inter-VDOM links
diagnose firewall iprope list
# 2. Check active iprope compilation state and conflict counters
diagnose firewall iprope state
# 3. Check global session collision counters
diagnose sys session stat
# 4. Filter sessions traversing inter-VDOM link interfaces
diagnose sys session filter clear
diagnose sys session filter intf npu0_vlink0
diagnose sys session listRemediation & Workaround Steps (Teaser Preview)
Follow the complete step-by-step remediation guide in the Ferrite interactive platform:
Frequently Asked Questions
The hardware iprope compiler fails to maintain VDOM namespace boundaries when generating translation tuples for shared NPU links, causing return packets to clash with active sessions in other VDOMs.
For moderate inter-VDOM throughput (< 2 Gbps), software VDOM links introduce negligible CPU overhead while completely avoiding the hardware iprope hash collision.
FortiOS 7.2.6, 7.4.1, and all subsequent builds introduce per-VDOM hash domain tags in the iprope compiler, eliminating translation tuple collisions.