Werk #18544: TCP Fetcher returns error if the host IP can't be resolved
| Component | Checks & agents | ||||
| Title | TCP Fetcher returns error if the host IP can't be resolved | ||||
| Date | Dec 9, 2025 | ||||
| Level | Prominent Change | ||||
| Class | Bug Fix | ||||
| Compatibility | Compatible - no manual interaction needed | ||||
| Checkmk versions & editions |
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The TCP fetcher now reports an error when it encounters the IP addresses 0.0.0.0 or ::. Previously, if the IP resolver failed to determine a valid IP address for a host and returned these addresses, the fetcher would silently fall back to the local system. This happened because the underlying socket library implicitly mapped 0.0.0.0 to 127.0.0.1 (localhost) when a local agent was installed, causing the fetcher to retrieve data from the local host instead of the intended remote host.
With this update, the TCP fetcher prevents this unintended fallback by explicitly reporting an error whenever it detects 0.0.0.0 or ::. As a result, users will no longer receive incorrect local data or experience silent failures. Instead, they will see a clear error message, which improves troubleshooting and helps identify issues with IP resolution.
No user action is required to benefit from this fix.