> For the complete documentation index, see [llms.txt](https://docs.adpage.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.adpage.io/faq/marketing-optimization/cross-domain-tracking-for-the-same-root-domain.md).

# Cross-domain tracking for the same root domain

## Cross-domain tracking for the same root domain

Cross-domain tracking is required when tracking visitors across domains that share the same root domain. For example, [**domainname.com**](http://domainname.com/) and [**subdomain.domainname.com**](http://subdomain.domainname.com/). This often applies to rental modules, scheduling modules, or personalization tools. They may run on a separate landing page or load in an iframe. When a visitor moves between domains or interacts with the iframe, marketing data must match on both pages.

### Solution 1: Conversion Linker in GTM

Add a Conversion Linker tag to the GTM web container. Add both domain names to the tag. The Conversion Linker passes click data and session parameters correctly between domains. This ensures conversions are attributed to the correct source.

[![](https://euw1.frontkb-cdn.com/attachments/9808087/547522/998e27f0-b763-48cc-a25d-cf7e77d2e39d.png)](https://euw1.frontkb-cdn.com/attachments/9808087/547522/998e27f0-b763-48cc-a25d-cf7e77d2e39d.png)

### Solution 2: Domain settings in GA4

In GA4, define which domains are treated as a single entity. Go to **Admin**, select **Data streams**, and choose the correct web stream. Open **Configure tag settings**, then select **Configure your domains**. Add all allowed domains, including the main domain and subdomain. GA4 then treats sessions across these domains as one continuous session.

[![](https://euw1.frontkb-cdn.com/attachments/9808087/547522/d3987c1e-e45f-46a6-b186-d47c7b95a45a.png)](https://euw1.frontkb-cdn.com/attachments/9808087/547522/d3987c1e-e45f-46a6-b186-d47c7b95a45a.png)

### Additional check: Consent Management Platform

Check that the subdomain is also added to the Consent Management Platform (CMP). This is often overlooked. If the subdomain is missing, consent signals cannot be retrieved correctly. Visitors without consent may then be tracked. Tracking may also fail completely. Both outcomes affect data quality and privacy compliance.


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