When a user logs on to a domain, a global catalog server is contacted to determine the universal group memberships of the ...

When a user logs on to a domain, a global catalog server is contacted to determine the universal group memberships of the user. If universal group membership caching in the site is not enabled and if a global catalog server is not available in the site, the domain controller must contact a global catalog server in another site over a potentially slow or unreliable wide area network (WAN), which can result in user authentication failures.