Symbian3/SDK/Source/GUID-6A78F618-09A9-56A7-8C58-98C353BF0788.dita
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     1 <?xml version="1.0" encoding="utf-8"?>
       
     2 <!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
       
     3 <!-- This component and the accompanying materials are made available under the terms of the License 
       
     4 "Eclipse Public License v1.0" which accompanies this distribution, 
       
     5 and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
       
     6 <!-- Initial Contributors:
       
     7     Nokia Corporation - initial contribution.
       
     8 Contributors: 
       
     9 -->
       
    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>