The DNS root zone consists of pointers to the authoritative domain name servers for all top-level domains (TLDs). The root zone is hosted on a collection of root servers operated by several organizations around the world that all use a specific, approved list of domains that is managed by ICANN. By contrast, alternative roots typically include pointers to all of the TLD servers for domains delegated by ICANN, as well as name servers for other, custom top-level domains that are not sanctioned by ICANN. Some alternate roots are operated by the organizations that manage these alternative TLDs.