to convert to an IP address. The host's DNS resolver sends a DNS query to a Recursive DNS Server (RDNSS) that has been configured in the host's DNS configuration (e.g., by means described in Section 3.10.2). The DNS query for www.example. com is received by a RDNSS, which has to first find what server is responsible for the com TLD. The RDNSS knows the root server Deploying IPv6 in 3GPP Networks "." Root 1) www.example.com? 3) Where is example.com? ".com" "example.com" Figure 1.4 DNS name resolution. addresses, and it sends the query to one of the root servers. The root server refers to the server responsible for com. 3. The RDNSS sends the query to the authoritative server responsible for com. This server responds by referring to the server responsible for example.com. 4. The RDNSS sends the query to DNS server authoritative for example. com. The DNS server answers with the DNS record that contains the IP address corresponding to www.example.com. 5. The RDNSS sends the record containing the IP address of www.example.com to the host. The IP addresses are stored in DNS records. The IPv4 records are stored in A [24] records, and the IPv6 addresses in AAAA records [25] (also called quad-A records). Please see more detailed implications of IPv6 to DNS in Sections 3.9.4 and 3.10.2. 1.6.3 Top Level Domain There are three categories of TLDs - gTLD, ccTLD, and infrastructure TLD. The Internet Assigned Number (IANA) Root Zone Database [26] lists the current TLDs. In the fol- lowing, the different TLD categories are explained. gTLD is a generic name TLD, which indicates something generic about the organizations or content on the next level. For instance, com indicates commercial, . org organiza- tion (usually non-for-profit), net network, and .mobi mobile communication. These indications are, however, not very strict in reality. A gTLD is always three or more latin characters long. The gTLDs are usually owned and operated by private organiza- tions, which sell or distribute the second level names to other organizations som