NT Authentication problem

I have a problem when getting NT logged-in user.

I am using bellow code to get NT user id. When I access the web site using "http://PCNAME/..... " or "http://localhost/...", it's working fine.

But if I use IP address, browser prompts Usename/ password dialog box. I can enter any username/password there.(Not authenticate correctly).
(I am using a local server for testing)

Please help me on this problem.

private static final boolean authenticateUser(HttpServletRequest request, HttpServletResponse response)
throws Exception{

System.out.println("Inside authenticateUser()....................");
try {
String auth = request.getHeader("Authorization");

if (auth == null) {
response.setContentLength(0);
response.setStatus(response.SC_UNAUTHORIZED);
response.setHeader("WWW-Authenticate", "NTLM");
return false;
}

if (!auth.startsWith("NTLM ")) {
throw new Exception("authenticateUser:Cannot authenticate user");
}

byte[] msg = new sun.misc.BASE64Decoder().decodeBuffer(auth.substring(5));

// Step 1: Negotiation message received
if (msg[8] == 1) {
// Send challenge message (Step 2)
response.setContentLength(2);
response.setStatus(response.SC_UNAUTHORIZED);
response.setHeader("WWW-Authenticate", "NTLM " + new sun.misc.BASE64Encoder().encodeBuffer(CHALLENGE_MESSAGE));
return false;
}

// Step 3: Authentication message received
if (msg[8] == 3) {
int off = 30;
int length, offset;

length = (msg[off+1]<<8) + msg[off];
offset = (msg[off+3]<<8) + msg[off+2];
String domain = removeBlanks(new String(msg, offset, length));

length = (msg[off+9]<<8) + msg[off+8];
offset = (msg[off+11]<<8) + msg[off+10];
String user = removeBlanks(new String(msg, offset, length));

length = (msg[off+17]<<8) + msg[off+16];
offset = (msg[off+19]<<8) + msg[off+18];
String ws = removeBlanks(new String(msg, offset, length));

System.out.println("Domain: " + domain + "<br>");
System.out.println("Username: " + user + "<br>");
System.out.println("Workstation: " + ws + "<br>");

request.getSession().setAttribute("user", user);
return true;
}
else {
throw new Exception("authenticateUser:Cannot authenticate user");
}
}
catch (Throwable ex){
throw new Exception("authenticateUser:" + ex.getMessage());
}
}//aut

Sudheer