1 <?xml version="1.0" encoding="utf-8"?>

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     4 "Eclipse Public License v1.0" which accompanies this distribution, 

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     7     Nokia Corporation - initial contribution.

     8 Contributors: 

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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-6A78F618-09A9-56A7-8C58-98C353BF0788" xml:lang="en"><title>Domain

    13 Name Server</title><shortdesc>The Domain Name Server (DNS) identifies the Internet servers based

    14 on the host names. This topic describes the concept of the DNS. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 <p>Internet communication is based on IP addresses, the DNS maps the host

    16 names to IP addresses. The DNS supports International Domain Names that contain

    17 ASCII and non-ASCII characters. </p>

    18 <section id="GUID-4592BB90-B123-4B0E-86BF-DB7EA3C49639"><title>Domain Name Server Proxy</title> <p>DNS Proxy server is a

    19 partial implementation of the DNS Server that runs on the standard DNS Server,

    20 port number 53. When DNS Proxy server is implemented on the Symbian platform,

    21 it forwards DNS requests or queries to the network DNS server for mapping

    22 the host names to IP addresses. DNS Proxy server resolves local names on the

    23 private network using the local DNS database. For standard internet domain

    24 names it uses external DNS server in the public network. </p> <p>The local

    25 name resolution is done using the local DNS database and the DNS. The DNS

    26 queries for standard internet domain name resolution are sent to the external

    27 DNS on one of the available uplinks. The Dynamic Host Configuration Protocol

    28 (DHCP) server updates the local database when the DHCP server assigns an IP

    29 address to the connecting local host on the private network. </p> </section>

    30 <section id="GUID-BAB306E6-5ABF-40A5-A938-3EC214A55558"><title>International Domain Names</title> <p>International Domain

    31 Names (IDN) can contain non-ASCII characters, the DNS uses a Punycode conversion

    32 library to resolve these domain names. When the Domain Name Daemon receives

    33 a domain name that contains non-ASCII characters it converts the domain name

    34 to Punycode. For more information about how the domain name is converted to

    35 Punycode see RFC 3492. By default, the support for IDN resolution is turned

    36 off. The library only converts UCS2.0 encoded domain names. </p> </section>

    37 <section id="GUID-B3928F70-373C-4971-A4D2-D7DBA9CA7477"><title>Top Level Domain (TLD) Whitelists and Backlists</title> <p>The

    38 support of International Domain Names threatens system security with homograph

    39 attacks, also known as phishing. The Symbian platform whitelist/blacklist

    40 URI service supports a whitelist/blacklist service for TLDs and a list of

    41 allowed characters for each TLD. This list is initialised when the system

    42 starts and can be edited using a sis package. </p> </section>

    43 </conbody><related-links>

    44 <link href="GUID-7510C121-A23F-50E0-8130-16AF552BC497.dita"><linktext>Dynamic Host

    45 Configuration Protocol</linktext></link>

    46 </related-links></concept>