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  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>