DV360 Cross-Domain Tracking

Overview

Cross-domain tracking allows Floodlight to maintain user session continuity across multiple domains or subdomains. This is critical for accurate conversion attribution when users navigate between your marketing site, e-commerce platform, and checkout pages on different domains.

Use Cases

• Marketing site (marketing.example.com) → E-commerce site (shop.example.com)
• Main website (example.com) → Checkout on third-party platform (checkout.partner.com)
• Multiple brand sites under same advertiser
• Subdomain transitions (www.example.com → app.example.com)
• International sites with different TLDs (example.com → example.co.uk)

How Floodlight Cross-Domain Tracking Works

Floodlight uses first-party cookies to track users. When a user crosses domains, the session data needs to be passed to maintain attribution continuity.

Default Behavior (Single Domain)

• Floodlight sets cookies on the current domain
• Cookies persist across pages within same domain
• Attribution works automatically

Cross-Domain Scenario

• User clicks DV360 ad → lands on marketing.example.com
• User navigates to shop.example.com (different domain)
• Without cross-domain tracking: session breaks, conversion not attributed
• With cross-domain tracking: session persists, conversion properly attributed

Implementation Methods

Method 1: Auto Linker (GTM - Recommended)

Google Tag Manager's auto-link functionality automatically appends Floodlight parameters to cross-domain links.

GTM Configuration

1. Create Floodlight Configuration Variable:

   • Variable Type: Google Floodlight Configuration
   • Advertiser ID: DC-XXXXXXXX
   • Auto-link domains: shop.example.com, checkout.example.com

2. Configure Auto-link Domains:

// In GTM, Floodlight Configuration tag settings
{
  'allow_ad_personalization_signals': true,
  'linker': {
    'domains': ['marketing.example.com', 'shop.example.com', 'checkout.example.com']
  }
}

3. Set Cookie Domain:
   • For subdomains: Set to '.example.com' (note the leading dot)
   • For different domains: Configure linker

GTM Tag Example

<script>
  gtag('config', 'DC-XXXXXXXX', {
    'linker': {
      'domains': ['marketing.example.com', 'shop.example.com'],
      'accept_incoming': true
    },
    'cookie_domain': 'auto',
    'cookie_flags': 'SameSite=None;Secure'
  });
</script>

Method 2: Manual Parameter Passing

For direct implementations without GTM, manually append Floodlight parameters to cross-domain links.

Implementation

// Add to all cross-domain links
function addFloodlightParams(url) {
  // Get Floodlight cookie value
  var flCookie = getCookie('_gcl_dc');

  if (flCookie) {
    var separator = url.indexOf('?') !== -1 ? '&' : '?';
    return url + separator + '_gcl_dc=' + encodeURIComponent(flCookie);
  }
  return url;
}

// Helper function to get cookie
function getCookie(name) {
  var value = "; " + document.cookie;
  var parts = value.split("; " + name + "=");
  if (parts.length == 2) return parts.pop().split(";").shift();
}

// Apply to links
document.querySelectorAll('a[href*="shop.example.com"]').forEach(function(link) {
  link.href = addFloodlightParams(link.href);
});

Method 3: Server-Side Implementation

For server-side tagging or when JavaScript isn't available:

// Server-side: Extract and forward Floodlight parameters
const floodlightParam = request.query._gcl_dc || request.cookies._gcl_dc;

if (floodlightParam) {
  // Set cookie on new domain
  response.cookie('_gcl_dc', floodlightParam, {
    domain: '.example.com',
    maxAge: 90 * 24 * 60 * 60 * 1000, // 90 days
    secure: true,
    sameSite: 'none'
  });
}

Configuration Steps

Step 1: Identify All Domains

List all domains and subdomains involved in user journey:

• Marketing sites
• Product/service sites
• E-commerce platforms
• Checkout systems
• Mobile app web views (if applicable)

Step 2: Configure Floodlight Settings

In Campaign Manager 360:

1. Navigate to Advertiser → Floodlight → Configuration
2. Review Cookie Settings
3. Ensure Counting Method supports cross-domain (typically "Standard")

Step 3: Implement Linker

Choose implementation method (GTM recommended):

GTM Auto-linker:

• Add all domains to linker configuration
• Enable "Accept incoming" parameter
• Test parameter passing

Manual linking:

• Update all cross-domain anchor tags
• Implement JavaScript to append parameters
• Test cookie persistence

Step 4: Test & Validate

1. Navigate from Domain A to Domain B
2. Check URL for _gcl_dc parameter
3. Verify cookie persists on Domain B
4. Trigger conversion and confirm attribution

Testing Cross-Domain Tracking

Browser DevTools Method

1. Open Chrome DevTools → Application → Cookies
2. Navigate to first domain (marketing.example.com)
3. Note _gcl_dc cookie value
4. Click cross-domain link
5. Check new domain (shop.example.com) for same _gcl_dc value
6. Verify cookie matches

GTM Preview Mode

1. Enable GTM Preview mode
2. Navigate through cross-domain journey
3. Check Tags tab for Floodlight Configuration
4. Verify linker parameters in Variables
5. Confirm tags fire on both domains

URL Parameter Verification

Cross-domain links should include _gcl_dc parameter:

https://shop.example.com/products?_gcl_dc=GCL.1234567890.CjwKCAiA...

Campaign Manager Test Conversions

1. Navigate from first domain with DV360 ad click
2. Complete cross-domain journey
3. Trigger conversion
4. Check Campaign Manager Test Conversions tool
5. Verify attribution to original click

Common Issues & Troubleshooting

Issue: Parameters Not Appending to Links

Causes:

• Linker domains not configured in GTM
• Links added dynamically after page load
• Form submissions (POST) losing parameters

Solutions:

• Add all domains to linker configuration
• Re-run linker script after dynamic content loads
• Use hidden form fields to preserve parameters

Issue: Cookie Not Persisting

Causes:

• Cookie domain mismatch
• SameSite restrictions
• Third-party cookie blocking

Solutions:

• Set cookie_domain to common parent (.example.com)
• Use SameSite=None;Secure for cross-site cookies
• Implement server-side cookie handling

Issue: Attribution Breaking

Causes:

• Parameter lost during redirect chains
• Cookie expiration
• Different Floodlight configurations on different domains

Solutions:

• Preserve parameters through all redirects
• Verify cookie expiration (default 90 days)
• Use same Floodlight configuration across all domains

Special Scenarios

Subdomain to Subdomain

For subdomains under same parent domain:

gtag('config', 'DC-XXXXXXXX', {
  'cookie_domain': '.example.com'  // Works for *.example.com
});

Third-Party Checkout Platform

When checkout is on partner domain:

// On your domain: append parameters to checkout link
<a href="https://checkout.partner.com/cart?_gcl_dc={{_gcl_dc}}"
   id="checkout-link">Proceed to Checkout</a>

// Partner implements: accept and set cookie
// Partner must deploy your Floodlight global tag

Mobile App Web Views

For attribution between mobile web and app web views:

// Pass parameter to web view
webView.loadUrl("https://example.com/checkout?_gcl_dc=" + floodlightValue);

// Implement universal links for seamless transition

Best Practices

• Use GTM auto-linker for simplest implementation
• Test cross-domain flow in all browsers (especially Safari with ITP)
• Set cookie_domain to broadest applicable domain (.example.com)
• Use SameSite=None;Secure for cross-site cookies
• Monitor attribution reports for unusual drop-offs between domains
• Document all domains in linker configuration
• Test after any domain changes or redirects
• Implement server-side fallback for cookie blocking scenarios
• Keep Floodlight configuration consistent across all domains
• Review and update domain list quarterly

Privacy & Compliance

• Disclose cross-domain tracking in privacy policy
• Implement consent management for EU users
• Respect user opt-out preferences across all domains
• Use first-party cookies when possible
• Consider server-side implementation for better privacy control
• Document data flows for GDPR compliance