Dhcp Server to Redirect Any Url to Landing Page

DHCP Server to Redirect any url to landing page

You appear to be trying to set up what's known as a captive portal.

There are several components to this, one of which is indeed a DHCP server, but that's hardly the most critical one.

A short overview

Your network will have at the very least the following components:

• DHCP server
• DNS server
• Gateway
• A login system

Clients will get an IP address from the DHCP server and will be told to use your DNS server and gateway.

Solution 1: DNS based redirection

Until users are logged in your DNS server replies with the IP address of the login web server. Take care to set a very low TTL on the DNS replies. You want to make sure the clients browser re-resolves the IP address after the login.

This will quite likely cause problems for any application other than web browsing on port 80.

Solution 2: TCP interception

This is a slightly harder solution, but is likely to work better.
The DNS server always returns the correct IP address for whatever web site the client is trying to reach.
The gateway will redirect the TCP sessions on port 80 to the login server.
All other packets should get an ICMP error reply (network unreachable for example).

How do I redirect to a page and not get a cached copy of the landing page

I just found a workaround:

I set another cookie after the login operation: "just-logged-in"
Added some javascript to the landing page that checks for the cookie "just-logged-in" and if it finds the cookie after deleting it (to avoid a reload loop) runs location.reload(true) which reloads the page ignoring the cache.

This results in another redirection but since the first one is read from the cache we have two HTTP requests as we expected.

Redirect a specific IP address to a special page of my homepage with .htaccess

Add a condition to not rewrite when you're already at specialpage:

RewriteCond %{REMOTE_ADDR} ^123\.\123\.123\.123$
RewriteCond %{REQUEST_URI} !/specialpage.php
RewriteRule ^(.*)$ /specialpage.php [R,L] 

Redirect domain name mapped with external IP (modem) to a host in its local network

If you want to redirect my domain to the particular host you need to setup NAT-Virtual Server Setup .

here you need to map remote port to internal map.

In above image IP address is my IP of my host and Default address is my router's IP address

Now you have configure NAT in you router as bellow.

in above image server IP is you host IP address.

I am using D-Link router so this Image is according to that if you are using some different router then you might have different view.

After configuring this when you type EXTERNAL_IP:80 your request will be forwarded to application that is running on you host with that port

Redirect website to unknown internal address

So I ended up going with the android app that scans the local subnet for the device. I have an html file on the server called knockknock.html that simply has the text "HELLO". For anyone interested, here's a first rendition of the code I'm using:

/*
 * Get the IP and subnet info and start scanning the local subnet
 */
void findServer() {
    WifiManager wifi = (WifiManager) this.getSystemService(Context.WIFI_SERVICE);

    DhcpInfo dhcp = wifi.getDhcpInfo();
    if (dhcp == null) {
        Log.d(TAG, "No DHCPInfo on WiFi side.");
    }

    //Get the string verison of the IP/subnet from the int given by WifiManager
    final String ip = intToIp(dhcp.ipAddress);
    final String mask = intToIp(dhcp.netmask);

    //Start the scanner on a separate thread from the UI
    Thread thread = new Thread() {
        @Override
        public void run() {
            serverScanner(ip, mask);
        }
    };

    thread.start();
}

/*
 * Convert an integer to a human readable format
 */
String intToIp(int i) {
    return  ( i & 0xFF) + "." +
            ((i >> 8 ) & 0xFF) + "." +
            ((i >> 16 ) & 0xFF) + "." +
            ((i >> 24 ) & 0xFF ) ;
}

/*
 * Scan the given subnet for the server
 */
void serverScanner(String ip, String netmask) {
    //Get the first part of the IP
    //TODO: Add support for various subnet masks
    String iIPv4 = ip.substring(0, ip.lastIndexOf("."));
    iIPv4 += ".";
    Log.v(TAG, "Current IP Structure: " + iIPv4);

    // Loop to scan each address on the local subnet
    for (int i = 1; i < 255; i++) {
        //Check to see if the server exists
        if (checkServer(iIPv4 + i)) {
            //It does exist, so let's set the variable and preferences
            mServerIP = iIPv4 + i;

            SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
            SharedPreferences.Editor editor = settings.edit();
            editor.putString("LastServerIP", mServerIP);
            editor.commit();
            return;  //And we're done here
        }
    }
}

/*
 * Send a request to the server and see if it's alive and what we're looking for
 */
boolean checkServer(String ip) {
    BufferedReader inputStream = null;

    try {

        HttpGet httpget = new HttpGet("http://" + ip + "/knockknock.html");
        HttpParams httpParameters = new BasicHttpParams();
        HttpConnectionParams.setConnectionTimeout(httpParameters, 100);
        HttpConnectionParams.setSoTimeout(httpParameters, 100);
        HttpClient httpclient = new DefaultHttpClient(httpParameters);

        HttpResponse response;
        response = httpclient.execute(httpget);

        HttpEntity entity = response.getEntity();

        if (entity != null) {

            InputStream instream = entity.getContent();
            String result = convertStreamToString(instream);
            instream.close();

            if (result.equals("HELLO\n")) {
                return true;
            }
        }
    } catch (Exception e) {
        Log.e(TAG, e.getMessage());
    }
    //No response or not the response we're looking for, so return false
    return false;
}

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