Received a question from a marketing friend who wanted to have some options for tracking across domains and sub-domains. Depending on how experienced your tech team is and which analytics package you have there are some options. Generally the following is true:

1) Distinguish between subdomains and domains – different rules apply for each from the standpoint of 1st vs 3rd party cookies. Sub-domains are XXX in http://xxx.yourdomain.com. It is an effective way to divide up your site among different servers and services.

2) You can use 3rd party cookies to store and track information like ID#’s for people moving among domains and sub-domains. Think ad serving like DART or Atlas and how it tracks view based impressions and activities. Same thing.

3) You can use 1st party cookies within a domain including sub-domains but not across domains. 1st party cookies have a higher acceptance rate than 3rd party cookies.

4) You’re other option is to pass everything in the query string between domains. We do this all the time, it’s a little more work when you execute pages (each link has to generate a code that gets passed from page to page) but gets around the cookie issues.

None of these options are perfect, but they should give some starting points in discussions with your development group.