In a multi-tier SMS hierarchy, if I enable User and User Group discovery on my Central site, will anything it discovers filter it's way down the hierarchy to all Primaries, or do I need to enable user/ user group discovery on all my Primaries?

Reason I ask in that in one of the white papers it says about only enabling User/ User Group discovery on one site in the domain to save the same resources being re-discovered several times, but it doesn't make it clear whether what's discovered on one Primary is filtered down to any primaries below it?

If you are sending advertisements to User Group collections, you will have to enable User/ User Group Discovery on not only your Central site, but also all your child Primaries. If you don't then users on your child sites won't receive these adverts until you enable User/ User Group Discovery at their Primary child site as this data is NOT passed between sites.

If you enable User/ User Group discovery at the Central site it will populate the CENTRAL site database only. However if you enable it at the child site it will populate the child site database as well as propagate the data up to the Central site. All database information is passed from child to parent, NOT from parent to child.

If you enable User/ User Group discovery on your Secondary sites (they share the database of the Primary with the other Secondaries that report to this Primary, and the Primary itself), if they are in the same domain it will generate duplicate information. If the Secondaries parent site has User/ User Group discovery enabled, their Collections will already have the discovery information in them so enabling it on the Secondary site(s) would be redundant.

If the Secondary sites are in a separate domain you could enable these discovery methods on them, however it would be easier to specify that domain in the parent's User/ User Group discovery properties.