The Domain Name Server (DNS) identifies the Internet servers based on the host names. This topic describes the concept of the DNS.
Internet communication is based on IP addresses, the DNS maps the host names to IP addresses. The DNS supports International Domain Names that contain ASCII and non-ASCII characters.
DNS Proxy server is a partial implementation of the DNS Server that runs on the standard DNS Server, port number 53. When DNS Proxy server is implemented on the Symbian platform, it forwards DNS requests or queries to the network DNS server for mapping the host names to IP addresses. DNS Proxy server resolves local names on the private network using the local DNS database. For standard internet domain names it uses external DNS server in the public network.
The local name resolution is done using the local DNS database and the DNS. The DNS queries for standard internet domain name resolution are sent to the external DNS on one of the available uplinks. The Dynamic Host Configuration Protocol (DHCP) server updates the local database when the DHCP server assigns an IP address to the connecting local host on the private network.
International Domain Names (IDN) can contain non-ASCII characters, the DNS uses a Punycode conversion library to resolve these domain names. When the Domain Name Daemon receives a domain name that contains non-ASCII characters it converts the domain name to Punycode. For more information about how the domain name is converted to Punycode see RFC 3492. By default, the support for IDN resolution is turned off. The library only converts UCS2.0 encoded domain names.
The support of International Domain Names threatens system security with homograph attacks, also known as phishing. The Symbian platform whitelist/blacklist URI service supports a whitelist/blacklist service for TLDs and a list of allowed characters for each TLD. This list is initialised when the system starts and can be edited using a sis package.
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