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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-6A78F618-09A9-56A7-8C58-98C353BF0788" xml:lang="en"><title>Domain
Name Server</title><shortdesc>The Domain Name Server (DNS) identifies the Internet servers based
on the host names. This topic describes the concept of the DNS. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>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. </p>
<section id="GUID-4592BB90-B123-4B0E-86BF-DB7EA3C49639"><title>Domain Name Server Proxy</title> <p>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. </p> <p>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. </p> </section>
<section id="GUID-BAB306E6-5ABF-40A5-A938-3EC214A55558"><title>International Domain Names</title> <p>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. </p> </section>
<section id="GUID-B3928F70-373C-4971-A4D2-D7DBA9CA7477"><title>Top Level Domain (TLD) Whitelists and Backlists</title> <p>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. </p> </section>
</conbody><related-links>
<link href="GUID-7510C121-A23F-50E0-8130-16AF552BC497.dita"><linktext>Dynamic Host
Configuration Protocol</linktext></link>
</related-links></concept>