.dd part of the Federal Republic of Germany, which had already been assigned the ccTLD .de. The ISO 3166-1 code "DD" was withdrawn in 1990. .dd .dd was the assigned country code top-level domain (ccTLD) for the German Democratic Republic (East Germany). It was chosen based on the ISO 3166-1 alpha-2 code for the German Democratic Republic, the letters coming from the German name of the country: '. In accordance with IANA policy, .dd was therefore available to be assigned as the country code top-level domain (ccTLD) for East Germany. However, this was never done, and so .dd was never added
Single-letter second-level domain if it should ever become available in the future. Single-letter second-level domain Single-letter second-level domains are domain names in which the second-level domain consists of only one letter, such as x.com. In 1993, the Internet Assigned Numbers Authority (IANA) explicitly reserved all single-letter and single-digit second-level domain names in the top-level domains com, net, and org, and grandfathered those that had already been assigned. In December 2005, ICANN considered auctioning these domains. On December 1, 1993, the Internet Assigned Numbers Authority (IANA) explicitly reserved the remaining single-letter and single-digit domain names. The few domains that were already assigned were grandfathered