Active Directory servers can have a “Global Catalog” that is exposed on a specific port. This allows searching the entire forest without referrals, for example to avoid issues with firewall configurations and DNS.
In such a case a response should contain all requested results which makes this method quicker and more reliable as there is only one server involved in the communication. However, consider that depending on the configuration, not all attributes may be replicated in the global catalog (see [Global Catalog & LDAP Searches]).