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| 1 | <!-- | ||
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| 25 | <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> | ||
| 26 | <HTML> | ||
| 27 | <HEAD> | ||
| 28 | <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=iso-8859-1"> | ||
| 29 | <TITLE>Networking Properties</TITLE> | ||
| 30 | </HEAD> | ||
| 31 | <BODY LANG="en-US" DIR="LTR"> | ||
| 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, java.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: <none>)<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=”*.foo.com|localhost”</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: <none>)<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: <none>)<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=”*.foo.com|localhost”</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: <none>)<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: <none>)<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: <none>)<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: “Java/<version>”)<BR> | ||
| 160 | Defines the string sent in the User-Agent request header in http | ||
| 161 | requests. Note that the string “Java/<version>” will | ||
| 162 | be appended to the one provided in the property (e.g. if | ||
| 163 | -Dhttp.agent=”foobar” is used, the User-Agent header will | ||
| 164 | contain “foobar Java/1.5.0” 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: <none>)<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 “cache forever” | ||
| 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 “cache forever”, 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 in the JRE security policy file <code>lib/security/java.security</code>.</P> | ||
| 241 | </BODY> | ||
| 242 | </HTML> | ||