Programmatically Retrieve Your IP Address Behind a Router / Proxy / Gateway

An IP Address (Internet Protocol Address) identifies and allows computers (printers, routers) to communicate with each other on a computer network.

The Internet is built on TCP/IP connections. The TCP part describes how two computers set up a connection to each other and transfer data. IP part primarily deals with how to get a message routed across the Internet.

If your machine is a part of a home (office) network you most probably have some kind of a router which joins the home's local area network (LAN) to the wide-area network (WAN) of the Internet.

Typically, the internal, LAN (Local Area Network) IP address is normally set to an IP number similar to "192.68.0.11".

The external, WAN (Wide Area Network) IP address of the router is set when the router connects to the Internet service provider.

If you need to know the WAN-IP of your router using Delphi code, you can take advantage of the "http://www.whatismyip.com" service which can reveal the IP address of machine:

WAN IP Address

 uses ScktComp;
 
 function GetHTML(const AURL: string): string;
 var
   sHead,sHost,sPage: string;
   x,xCnt,xCntTotal: integer;
   sock: TClientSocket;
   ws: TWinSocketStream;
   ss: TStringStream;
   buff: array[0..4095] of char;
 const
   CrLf = #13#10;
 begin
   Result := '';
 
   sHost := AURL;
   x := Pos('//',sHost) ;
   if x > 0 then
     System.Delete(sHost,1,x+1) ;
   x := Pos('/',sHost) ;
   if x > 0 then
   begin
     sPage := Copy(sHost,x,Length(sHost)) ;
     System.Delete(sHost,x,Length(sHost)) ;
   end
   else
   begin
     sPage := '/';
   end;
 
   sock := TClientSocket.Create(nil) ;
   try
     try
       sock.ClientType := ctBlocking;
       sock.Port := 80;
       sock.Host := sHost;
       sock.Open;
 
       // set timeout to 20 seconds
       ws := TWinSocketStream.Create(sock.Socket,20000) ;
       ss := TStringStream.Create('') ;
       try
         sHead := 'GET ' + sPage + ' HTTP/1.0 ' + CrLf + 'Host: ' + sHost + CrLf + CrLf;
         StrPCopy(buff,sHead) ;
 
         ws.Write(buff,Length(sHead) + 1) ;
         ws.Position := 0;
 
         FillChar(buff,SizeOf(buff),0) ;
         repeat
           xCnt := ws.Read(buff,SizeOf(buff)) ;
           xCntTotal := xCntTotal + xCnt;
           ss.Write(buff[0],xCnt) ;
         until xCnt = 0;
 
         Result := ss.DataString;
       finally
         ws.Free;
         ss.Free;
       end;
     except
   end;
   finally
     sock.Free;
   end;
 end; 

Here's how to use the above function to get your WAN IP from the www.whatismyip.com:

 var
   ip: string;
 begin
   with TStringlist.Create do
   try
     Text := GetHTML('www.whatismyip.com/automation/n09230945.asp') ;
     if Count > 0 then ip := Strings[Count - 1];
   finally
     Free;
   end;
   ShowMessage('Your (gateway / router / proxy) IP address is ' + ip) ;
 end; 

Note: if you need to programmatically determine the LAN IP address of a machine running your Delphi application, the My LAN IP with Delphi provides the code you can use.

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• internet programming
• ip helper api
• tcp / sockets communication