# Operation modes The URL in the CG1018 can be configured in three different modes depending on server type which can be B3, B2 or Coolguard (RQS): * MAC mode is used for B3 where the SERVICE\_URL is defined by MAC address, * DUAL mode is used for B2 or Coolguard (RQS) with two SERVICE\_URL’s where only sensor alarms affect two relays, * SINGLE mode which is an old standard, where both relays are controlled by a sensor and communication alarms from a single URL. DUAL and SINGLE modes are compatible with a previous version of Relay Box, with only two relays. {% hint style="info" %} Note that you can use only **one mode at a time**. {% endhint %} --- # 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://help.boomerang3.com/cg1018-relay-box-installation-manual/installation/config-file/url__3_different_modes.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.