# Host Checking Host checking uses an additional network check between all hosts in a link. These checks are used to detect network partitions and discover the best link to activate in a high availability configuration. All link clients must be updated to v1.2 to support host checking. This feature is optional but if the port is not opened the link page will show the link hosts as offline. **The client must have access to TCP port 9790 on all other hosts.** --- # Agent Instructions: 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: ``` GET https://docs.pritunl.com/kb/vpn/link/host-checking.md?ask= ``` The question should be specific, self-contained, and written in natural language. 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.