> For the complete documentation index, see [llms.txt](https://docs.fusion.vectra.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.fusion.vectra.ai/detection-models/library/post-compromise/uncommon_icmp_reject.md). # uncommon\_icmp\_reject **Explanation** The uncommon\_icmp\_reject event is triggered when the Netography Detection Module (NDM) detects network flows for ICMP messages that indicate that there is traffic on the network that is being administratively prohibited (blocked). **What to Look For** Typically, these ICMP messages are sent in response to traffic that is being blocked by a firewall, either at the host or network level. In some cases this could be a sign that a network is compromised, and the attacker is running scans or attempting to access parts of the network that are firewalled. These events could also be triggered by misconfigurations or authorized network scanning activity. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.fusion.vectra.ai/detection-models/library/post-compromise/uncommon_icmp_reject.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.