Examples of java.net.InetAddress

java.net.InetAddress

etf.org/rfc/rfc790.txt">RFC 790: Assigned Numbers, RFC 1918: Address Allocation for Private Internets, RFC 2365: Administratively Scoped IP Multicast, and RFC 2373: IP Version 6 Addressing Architecture. An instance of an InetAddress consists of an IP address and possibly its corresponding host name (depending on whether it is constructed with a host name or whether it has already done reverse host name resolution).

Address types

unicast An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address.
The Unspecified Address -- Also called anylocal or wildcard address. It must never be assigned to any node. It indicates the absence of an address. One example of its use is as the target of bind, which allows a server to accept a client connection on any interface, in case the server host has multiple interfaces.
The unspecified address must not be used as the destination address of an IP packet.
The Loopback Addresses -- This is the address assigned to the loopback interface. Anything sent to this IP address loops around and becomes IP input on the local host. This address is often used when testing a client.

multicast An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces identified by that address.

unicast	An identifier for a single interface. A packet sent to a unicast address is delivered to the interface identified by that address. The Unspecified Address -- Also called anylocal or wildcard address. It must never be assigned to any node. It indicates the absence of an address. One example of its use is as the target of bind, which allows a server to accept a client connection on any interface, in case the server host has multiple interfaces. The unspecified address must not be used as the destination address of an IP packet. The Loopback Addresses -- This is the address assigned to the loopback interface. Anything sent to this IP address loops around and becomes IP input on the local host. This address is often used when testing a client.
multicast	An identifier for a set of interfaces (typically belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces identified by that address.

IP address scope

Link-local addresses are designed to be used for addressing on a single link for purposes such as auto-address configuration, neighbor discovery, or when no routers are present.

Site-local addresses are designed to be used for addressing inside of a site without the need for a global prefix.

Global addresses are unique across the internet.

Textual representation of IP addresses

The textual representation of an IP address is address family specific.

For IPv4 address format, please refer to Inet4Address#format; For IPv6 address format, please refer to Inet6Address#format.

Host Name Resolution

Host name-to-IP address resolution is accomplished through the use of a combination of local machine configuration information and network naming services such as the Domain Name System (DNS) and Network Information Service(NIS). The particular naming services(s) being used is by default the local machine configured one. For any host name, its corresponding IP address is returned.

Reverse name resolution means that for any IP address, the host associated with the IP address is returned.

The InetAddress class provides methods to resolve host names to their IP addresses and vice versa.

InetAddress Caching

The InetAddress class has a cache to store successful as well as unsuccessful host name resolutions.

By default, when a security manager is installed, in order to protect against DNS spoofing attacks, the result of positive host name resolutions are cached forever. When a security manager is not installed, the default behavior is to cache entries for a finite (implementation dependent) period of time. The result of unsuccessful host name resolution is cached for a very short period of time (10 seconds) to improve performance.

If the default behavior is not desired, then a Java security property can be set to a different Time-to-live (TTL) value for positive caching. Likewise, a system admin can configure a different negative caching TTL value when needed.

Two Java security properties control the TTL values used for positive and negative host name resolution caching:

networkaddress.cache.ttl

Indicates the caching policy for successful name lookups from the name service. The value is specified as as integer to indicate the number of seconds to cache the successful lookup. The default setting is to cache for an implementation specific period of time.
A value of -1 indicates "cache forever".

networkaddress.cache.negative.ttl (default: 10)

Indicates the caching policy for un-successful name lookups from the name service. The value is specified as as integer to indicate the number of seconds to cache the failure for un-successful lookups.
A value of 0 indicates "never cache". A value of -1 indicates "cache forever".

@author Chris Warth @version 1.116, 09/05/07 @see java.net.InetAddress#getByAddress(byte[]) @see java.net.InetAddress#getByAddress(java.lang.String,byte[]) @see java.net.InetAddress#getAllByName(java.lang.String) @see java.net.InetAddress#getByName(java.lang.String) @see java.net.InetAddress#getLocalHost() @since JDK1.0

            
          Enumeration addresses = ni.getInetAddresses();
          
          while( addresses.hasMoreElements()){
            
            InetAddress address = (InetAddress)addresses.nextElement();
            
            if ( address.isLoopbackAddress() || address instanceof Inet6Address ){
              
              continue;
            }
            
            return( address );

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    if ( Constants.isCVSVersion()){
    
        // allow local addresses for testing
      
      try{
        InetAddress ia = InetAddress.getByName( host );
      
        return( ia.isLoopbackAddress() || ia.isLinkLocalAddress() || ia.isSiteLocalAddress());
        
      }catch( Throwable e ){
      }
    }

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    boolean                  upnp_map,
    NetworkAdminProgressListener      listener )
  
    throws NetworkAdminException
  {
    InetAddress bind_ip = address==null?null:address.getAddress();
    
    NetworkAdminProtocolTester  tester;
    
    if ( type == PT_HTTP ){
      
      tester = new NetworkAdminHTTPTester( core, listener );
      
    }else if ( type == PT_TCP ){
      
      tester = new NetworkAdminTCPTester( core, listener );


    }else{
      
      tester = new NetworkAdminUDPTester( core, listener );
    }
    
    InetAddress  res;
    
    if ( port <= 0 ){
      
      res = tester.testOutbound( bind_ip, 0 );

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  {


    int  pos = bgp_prefix.indexOf('/');
    
    try{
      InetAddress  start = InetAddress.getByName( bgp_prefix.substring(0,pos));
      
      int  cidr_mask = Integer.parseInt( bgp_prefix.substring( pos+1 ));
      
      int  rev_mask = 0;
      
      for (int i=0;i<32-cidr_mask;i++){
        
      
        rev_mask = ( rev_mask << 1 ) | 1;
      }
      
      byte[]  bytes = start.getAddress();
      
      bytes[0] |= (rev_mask>>24)&0xff;
      bytes[1] |= (rev_mask>>16)&0xff;
      bytes[2] |= (rev_mask>>8)&0xff;
      bytes[3] |= (rev_mask)&0xff;

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        return( true );
      }
      
        // allow local addresses for testing purposes
      
      InetAddress iad = InetAddress.getByName(host);
      
      if (   iad.isLoopbackAddress() ||
          iad.isLinkLocalAddress() ||
          iad.isSiteLocalAddress()){
        
        return( true );
      }
    }catch( Throwable e ){
    }

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      return( false );
    }
    
    try{
      InetAddress  start  = getCIDRStartAddress();
      InetAddress  end    = getCIDREndAddress();
      
      long  l_start = PRHelpers.addressToLong( start );
      long  l_end  = PRHelpers.addressToLong( end );
      
      long  test = PRHelpers.addressToLong( address );

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    InetSocketAddress  address,
    byte        protocol_version )
  
    throws DHTTransportException
  {    
    InetAddress ia = address.getAddress();
    
    if ( ia == null ){
      
      // Debug.out( "Address '" + address + "' is unresolved" );
      
      throw( new DHTTransportException( "Address '" + address + "' is unresolved" ));
      
    }else{
      
      String  key;
      
      if ( protocol_version >= DHTTransportUDP.PROTOCOL_VERSION_RESTRICT_ID3 ){
        
        byte[] bytes = ia.getAddress();
        
        if ( bytes.length == 4 ){
          
          //final long K0  = Long.MAX_VALUE;  
          //final long K1  = Long.MAX_VALUE;  
          
            // restrictions suggested by UoW researchers as effective at reducing Sybil opportunity but 
            // not so restrictive as to impact DHT performance
          
          final long K2  = 2500;
          final long K3  = 50;
          final long K4  = 5;


          long  result = address.getPort() % K4;
          
          result = ((((long)bytes[3] << 8 ) &0x000000ff00L ) | result ) % K3;
          result = ((((long)bytes[2] << 16 )&0x0000ff0000L ) | result ) % K2;
          result = ((((long)bytes[1] << 24 )&0x00ff000000L ) | result ); // % K1;
          result = ((((long)bytes[0] << 32 )&0xff00000000L ) | result ); // % K0;


          key = String.valueOf( result );
                    
        }else{


            // stick with existing approach for IPv6 at the moment
          
          key = ia.getHostAddress() + ":" + ( address.getPort() % 8 );
        }
      }else if ( protocol_version >= DHTTransportUDP.PROTOCOL_VERSION_RESTRICT_ID_PORTS2 ){


          // more draconian limit, analysis shows that of 500,000 node addresses only
          // 0.01% had >= 8 ports active. ( 1% had 2 ports, 0.1% 3)
          // Having > 1 node with the same ID doesn't actually cause too much grief
    
        key = ia.getHostAddress() + ":" + ( address.getPort() % 8 );
        
      }else if ( protocol_version >= DHTTransportUDP.PROTOCOL_VERSION_RESTRICT_ID_PORTS ){


          // limit range to around 2000 (1999 is prime)


        key = ia.getHostAddress() + ":" + ( address.getPort() % 1999 );
        
      }else{
      
        key = ia.getHostAddress() + ":" + address.getPort();
      }
      
      synchronized( node_id_history ){
        
        byte[]  res = node_id_history.get( key );

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    DataOutputStream  os,
    InetSocketAddress  address )
  
    throws IOException, DHTTransportException
  {
    InetAddress  ia = address.getAddress();
    
    if ( ia == null ){
      
      Debug.out( "Address '" + address + "' is unresolved" );
      
      throw( new DHTTransportException( "Address '" + address + "' is unresolved" ));
    }
    
    serialiseByteArray( os, ia.getAddress(), 16);  // 16 (Pv6) + 1 length
    
    os.writeShort( address.getPort());  //19
  }

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  protected PeerItem( String _address, int _tcp_port, byte _source, byte _handshake, int _udp_port, byte _crypto_level, int _up_speed  ) {
    byte[] raw;
    try{
      //see if we can resolve the address into a compact raw IPv4/6 byte array (4 or 16 bytes)
      InetAddress ip = InetAddress.getByName( _address );
      raw = ip.getAddress();
    }
    catch( UnknownHostException e ) {
      //not a standard IPv4/6 address, so just use the full string bytes
      raw = _address.getBytes();
    }

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        getPort() != other.getPort()){
      
      return( false );
    }
    
    InetAddress e1 = getExternalAddress();
    InetAddress e2 = other.getExternalAddress();
    
    if ( e1 == null && e2 == null ){
      
      return( true );
    }

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