In case we fail to resolve backup resolver address, we take the IP address of the default backup resolver.

resources/config/defaults.properties

@@ -69,3 +69,7 @@ plugin.simpleaccreg.PROTOCOL_ORDER=SIP|MSN|Yahoo|ICQ|AIM|Jabber
 plugin.provisioning.DEFAULT_PROVISIONING_METHOD=
 
 plugin.updatechecker.package.name=sip-communicator
+
+# IP address of the backup resolver
+util.dns.BACKUP_RESOLVER_IP=8.8.8.8
+

src/net/java/sip/communicator/util/NetworkUtils.java

@@ -98,6 +98,13 @@ public class NetworkUtils
     public static final String DEFAULT_BACKUP_RESOLVER
         = "backup-resolver.jitsi.net";
 
+    /**
+     * The name of the system property that users may use to override the
+     * IP address of our backup DNS resolver.
+     */
+    public static final String PNAME_BACKUP_RESOLVER_IP
+        = "util.dns.BACKUP_RESOLVER_IP";
+
     /**
      * The DNSjava resolver that we use with SRV and NAPTR queries in order to
      * try and smooth the problem of DNS servers that silently drop them.
@@ -1025,14 +1032,23 @@ private static Lookup createLookup(String domain, int type)
             {
                 String customRslvrAddr
                     = System.getProperty(PNAME_BACKUP_RESOLVER);
-
                 String rslvrAddrStr = DEFAULT_BACKUP_RESOLVER;
+                String customRslvrIP
+                    = UtilActivator.getResources().getSettingsString(
+                        PNAME_BACKUP_RESOLVER_IP);
 
                 if(! StringUtils.isNullOrEmpty( customRslvrAddr ))
                     rslvrAddrStr = customRslvrAddr;
 
-                InetAddress resolverAddress
-                    = getInetAddress(rslvrAddrStr);
+                InetAddress resolverAddress = getInetAddress(rslvrAddrStr);
+
+                if(resolverAddress == null)
+                {
+                    /* name resolution failed for backup DNS resolver,
+                     * try with the IP address of the default backup resolver
+                     */
+                    resolverAddress = getInetAddress(customRslvrIP);
+                }
 
                 int rslvrPort = SimpleResolver.DEFAULT_PORT;