> For the complete documentation index, see [llms.txt](https://help.boomerang3.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.boomerang3.com/cg1018-relay-box-installation-manual/installation/config-file/url__3_different_modes.md).

# 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 %}


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