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  29         <TITLE>Networking Properties</TITLE>
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  32 <H1 ALIGN=CENTER>Networking Properties</H1>
  33 <P ALIGN=LEFT>There are a few standard system properties used to
  34 alter the mechanisms and behavior of the various classes of the
  35 java.net package. Some are checked only once at startup of the VM,
  36 and therefore are best set using the -D option of the java command,
  37 while others have a more dynamic nature and can also be changed using
  38 the <a href="../../lang/System.html#setProperty(java.lang.String,%20java.lang.String)">System.setProperty()</a> API. The purpose of this document is to list
  39 and detail all of these properties.</P>
  40 <P>If there is no special note, a property value is checked every time it is used.</P>
  41 <a name="Ipv4IPv6"></a>
  42 <H2>IPv4 / IPv6</H2>
  43 <UL>
  44         <LI><P><B>java.net.preferIPv4Stack</B> (default: false)<BR>
  45         If IPv6 is available on the operating system the
  46         underlying native socket will be, by default, an IPv6 socket which
  47         lets applications connect to, and accept connections from, both
  48         IPv4 and IPv6 hosts. However, in the case an application would
  49         rather use IPv4 only sockets, then this property can be set to <B>true</B>.
  50         The implication is that it will not be possible for the application
  51         to communicate with IPv6 only hosts.</P>
  52         <LI><P><B>java.net.preferIPv6Addresses</B> (default: false)<BR>
  53         When dealing with a host which has both IPv4
  54         and IPv6 addresses, and if IPv6 is available on the operating
  55         system, the default behavior is to prefer using IPv4 addresses over
  56         IPv6 ones. This is to ensure backward compatibility, for example
  57         applications that depend on the representation of an IPv4 address
  58         (e.g. 192.168.1.1). This property can be set to <B>true</B> to
  59         change that preference and use IPv6 addresses over IPv4 ones where
  60         possible.</P>
  61 </UL>
  62 <P>Both of these properties are checked only once, at startup.</P>
  63 <a name="Proxies"></a>
  64 <H2>Proxies</H2>
  65 <P>A proxy server allows indirect connection to network services and
  66 is used mainly for security (to get through firewalls) and
  67 performance reasons (proxies often do provide caching mechanisms).
  68 The following properties allow for configuration of the various type
  69 of proxies.</P>
  70 <UL>
  71         <LI><P>HTTP</P>
  72         <P>The following proxy settings are used by the HTTP protocol handler.</P>
  73         <UL>
  74                 <LI><P><B>http.proxyHost</B> (default: &lt;none&gt;)<BR>
  75                 The hostname, or address, of the proxy server 
  76                 </P>
  77                 <LI><P><B>http.proxyPort</B> (default: 80)<BR>
  78                 The port number of the proxy server.</P>
  79                 <LI><P><B>http.nonProxyHosts</B> (default:  localhost|127.*|[::1])<BR>
  80                 Indicates the hosts that should be accessed without going
  81                 through the proxy. Typically this defines internal hosts.
  82                 The value of this property is a list of hosts,
  83                 separated by the '|' character. In addition the wildcard
  84                 character '*' can be used for pattern matching. For example
  85                 <code>-Dhttp.nonProxyHosts=&rdquo;*.foo.com|localhost&rdquo;</code>
  86                 will indicate that every hosts in the foo.com domain and the
  87                 localhost should be accessed directly even if a proxy server is
  88                 specified.</P>
  89                 <P>The default value excludes all common variations of the loopback address.</P>
  90         </UL>
  91         <LI><P>HTTPS<BR>This is HTTP over SSL, a secure version of HTTP
  92         mainly used when confidentiality (like on payment sites) is needed.</P>
  93         <P>The following proxy settings are used by the HTTPS protocol handler.</P>
  94         <UL>
  95                 <LI><P><B>https.proxyHost</B>(default: &lt;none&gt;)<BR>
  96                 The hostname, or address, of the proxy server 
  97                 </P>
  98                 <LI><P><B>https.proxyPort</B> (default: 443)<BR>
  99                 The port number of the proxy server.</P>
 100                 <P>The HTTPS protocol handler will use the same nonProxyHosts
 101                 property as the HTTP protocol.</P>
 102         </UL>
 103         <LI><P>FTP</P>
 104         <P>The following proxy settings are used by the FTP protocol handler.</P>
 105         <UL>
 106                 <LI><P><B>ftp.proxyHost</B>(default: &lt;none&gt;)<BR>
 107                 The hostname, or address, of the proxy server 
 108                 </P>
 109                 <LI><P><B>ftp.proxyPort</B> (default: 80)<BR>
 110                 The port number of the proxy server.</P>
 111                 <LI><P><B>ftp.nonProxyHosts</B> (default: localhost|127.*|[::1])<BR>
 112                 Indicates the hosts that should be accessed without going
 113                 through the proxy. Typically this defines internal hosts.
 114                 The value of this property is a list of hosts, separated by
 115                 the '|' character. In addition the wildcard character
 116                 '*' can be used for pattern matching. For example
 117                 <code>-Dhttp.nonProxyHosts=&rdquo;*.foo.com|localhost&rdquo;</code>
 118                 will indicate that every hosts in the foo.com domain and the
 119                 localhost should be accessed directly even if a proxy server is
 120                 specified.</P>
 121                 <P>The default value excludes all common variations of the loopback address.</P>
 122         </UL>
 123         <LI><P>SOCKS<BR>This is another type of proxy. It allows for lower
 124         level type of tunneling since it works at the TCP level. In effect,
 125         in the Java(tm) platform setting a SOCKS proxy server will result in
 126         all TCP connections to go through that proxy, unless other proxies
 127         are specified. If SOCKS is supported by a Java SE implementation, the
 128         following properties will be used:</P>
 129         <UL>
 130                 <LI><P><B>socksProxyHost</B> (default: &lt;none&gt;)<BR>
 131                 The hostname, or address, of the proxy server.</P>
 132                 <LI><P><B>socksProxyPort</B> (default: 1080)<BR>
 133                 The port number of the proxy server.</P>
 134                 <LI><P><B>socksProxyVersion</B> (default: 5)<BR>
 135                 The version of the SOCKS protocol supported by the server. The
 136                 default is <code>5</code> indicating SOCKS V5, alternatively
 137                 <code>4</code> can be specified for SOCKS V4. Setting the property
 138                 to values other than these leads to unspecified behavior.</P>
 139                 <LI><P><B>java.net.socks.username</B> (default: &lt;none&gt;)<BR>
 140                 Username to use if the SOCKSv5 server asks for authentication
 141                 and no java.net.Authenticator instance was found.</P>
 142                 <LI><P><B>java.net.socks.password</B> (default: &lt;none&gt;)<BR>
 143                 Password to use if the SOCKSv5 server asks for authentication
 144                 and no java.net.Authenticator instance was found.</P>
 145                 <P>Note that if no authentication is provided with either the above
 146                 properties or an Authenticator, and the proxy requires one, then
 147                 the <B>user.name</B> property will be used with no password.</P>
 148         </UL>
 149         <LI><P><B>java.net.useSystemProxies</B> (default: false)<BR>
 150         On recent Windows systems and on Gnome 2.x systems it is possible to
 151         tell the java.net stack, setting this property to <B>true</B>, to use
 152         the system proxy settings (both these systems let you set proxies
 153         globally through their user interface). Note that this property is
 154         checked only once at startup.</P>
 155 </UL>
 156 <a name="MiscHTTP"></a>
 157 <H2>Misc HTTP properties</H2>
 158 <UL>
 159         <LI><P><B>http.agent</B> (default: &ldquo;Java/&lt;version&gt;&rdquo;)<BR>
 160         Defines the string sent in the User-Agent request header in http
 161         requests. Note that the string &ldquo;Java/&lt;version&gt;&rdquo; will
 162         be appended to the one provided in the property (e.g. if 
 163         -Dhttp.agent=&rdquo;foobar&rdquo; is used, the User-Agent header will
 164         contain &ldquo;foobar Java/1.5.0&rdquo; if the version of the VM is
 165         1.5.0). This property is checked only once at startup.</P>
 166         <LI><P><B>http.keepalive</B> (default: true)<BR>
 167         Indicates if persistent connections should be supported. They improve
 168         performance by allowing the underlying socket connection to be reused
 169         for multiple http requests. If this is set to true then persistent
 170         connections will be requested with HTTP 1.1 servers.</P>
 171         <LI><P><B>http.maxConnections</B> (default: 5)<BR>
 172         If HTTP keepalive is enabled (see above) this value determines the
 173         maximum number of idle connections that will be simultaneously kept
 174         alive, per destination.</P>
 175         <LI><P><B>http.maxRedirects</B> (default: 20)<BR>
 176         This integer value determines the maximum number, for a given request,
 177         of HTTP redirects that will be automatically followed by the
 178         protocol handler.</P>
 179         <LI><P><B>http.auth.digest.validateServer</B> (default: false)</P>
 180         <LI><P><B>http.auth.digest.validateProxy</B> (default: false)</P>
 181         <LI><P><B>http.auth.digest.cnonceRepeat</B> (default: 5)</P>
 182         <P>These 3 properties modify the behavior of the HTTP digest
 183         authentication mechanism. Digest authentication provides a limited
 184         ability for the server  to authenticate itself to the client (i.e.
 185         By proving it knows the user's password). However not all HTTP
 186         servers support this capability and by default it is turned off. The
 187         first two properties can be set to true to enforce this check for
 188         authentication with either an origin or proxy server, respectively.</P>
 189         <P>It is usually not necessary to change the third property. It
 190         determines how many times a cnonce value is re-used. This can be
 191         useful when the MD5-sess algorithm is being used. Increasing this
 192         value reduces the computational overhead on both client and server
 193         by reducing the amount of material that has to be hashed for each
 194         HTTP request.</P>
 195         <LI><P><B>http.auth.ntlm.domain</B> (default: &lt;none&gt;)<BR>
 196         NTLM is another authentication scheme. It uses the
 197         java.net.Authenticator class to acquire usernames and passwords when
 198         they are needed. However NTLM also needs the NT domain name. There are
 199         3 options for specifying that domain:</P>
 200         <OL>
 201           <LI><P>Do not specify it. In some environments the domain is
 202               actually not required and the application does not have to specify
 203               it.</P>
 204           <LI><P>The domain name can be encoded within the username by
 205               prefixing the domain name, followed by a back-slash '\' before the
 206               username. With this method existing applications that use the
 207               authenticator class do not need to be modified, as long as users
 208               are made aware that this notation must be used.</P>
 209           <LI><P>If a domain name is not specified as in method 2) and these
 210               property is defined, then its value will be used a the domain
 211               name.</P>
 212         </OL>
 213 </UL>
 214 <P>All these properties are checked only once at startup.</P>
 215 <a name="AddressCache"></a>
 216 <H2>Address Cache</H2>
 217 <P>The java.net package, when doing name resolution, uses an address
 218 cache for both security and performance reasons. Any address
 219 resolution attempt, be it forward (name to IP address) or reverse (IP
 220 address to name), will have its result cached, whether it was
 221 successful or not, so that subsequent identical requests will not
 222 have to access the naming service. These properties allow for some
 223 tuning on how the cache is operating.</P>
 224 <UL>
 225         <LI><P><B>networkaddress.cache.ttl</B> (default: see below)<BR>
 226         Value is an integer corresponding to the number of seconds successful
 227         name lookups will be kept in the cache. A value of -1, or any  other
 228         negative value for that matter, indicates a &ldquo;cache forever&rdquo;
 229         policy, while a value of 0 (zero) means no caching. The default value
 230         is -1 (forever) if a security manager is installed, and implementation
 231         specific when no security manager is installed.</P>
 232         <LI><P><B>networkaddress.cache.negative.ttl</B> (default: 10)<BR>
 233         Value is an integer corresponding to the number of seconds an
 234         unsuccessful name lookup will be kept in the cache. A value of -1,
 235         or any negative value, means &ldquo;cache forever&rdquo;, while a
 236         value of 0 (zero) means no caching.</P>
 237 </UL>
 238 <P>Since these 2 properties are part of the security policy, they are
 239 not set by either the -D option or the System.setProperty() API,
 240 instead they are set as security properties.</P>
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