Linux web hosting and server support tips

Category: Windows Server

Restrict access to website using IP address in IIS 7

We can restrict the access to a website using IP addresses or domain name in IIS 7 easily using the “IP and Domain Restrictions” module. Unlike IIS 6, this module is not enabled by default when you install Internet Information Services (IIS). we need to install it. But don’t worry, this can also be done easily through Server Manager.

You can follow the below step by step instruction:-

 

Enabling the “IP and Domain Restrictions” module

1. Open the Server Manager by selecting the path Start > Administrative Tools > Server Manager.

2. Click “Add Role Services” link to add the required Role. Check the “IP and Domain Restrictions” check box in “Select Role Services” screen and click “Next” to continue and complete the module installation. If the module is already installed, it will show as “installed”.

 

 

 

Configuring the “IP and Domain Restrictions” module

 

1. Start Internet Information Services (IIS) and open “IP and Domain Restrictions”.

 

Click to enlarge the image

Click to enlarge the image

2. Inside IPv4 Addresses and Domain Restrictions, select “Add Allow Entry” or “Add Deny Entry” to add Allow or Deny entries. You can specify IP address, an IP address range or a Domain Name.

Click to enlarge the image

Click to enlarge the image

 

 

3. For setting default policy, Click on “Edit feature settings” and select “Allow” or “Deny” as required.

 

 

Click to enlarge the image

Click to enlarge the image

Note:-

1. Please note that configuring Allow or Deny restrictions using Domain name require reverse DNS look up every time a request arrives the server. Performing reverse DNS lookups is a potentially expensive operation that can severely degrade the performance of your IIS server.
2. IP entries are applied instantly without the need for a restart of the site or iis. The entries are processed in order so if you place deny and allow entries in the wrong order then you may lock the incorrect people out of the website.

Distributed Denial of service(DDOS)

A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a computer or network resource unavailable to its intended users. The speciality of the DDOS is that, it relays attacks not from a single network/host like DOS. The DDOS attack will be launched from different dynamic networks which has already been compromised.

Types:-

Ping of death :-
Attacker deliverately sending a ping packet, normally 64 bytes, that is larger than the 65,535 bytes. Many computer systems cannot handle an IP packet larger than the maximum IP packet size of 65,535, and often causes computer systems crash. A ping packet of size greater than 65,535, can be sent if it is fragmented.When a receiving computer reassembles the packet, a buffer overflow occurs, which often causes computer to crash.

Ping of flood:-
An attacker overwhelming the victim’s network with ICMP Echo Request (ping) packets. A flood of ping traffic can consume singificant bandwidth on low to mid-speed networks bringing down a network to a crawl.

Smurf Attack:-
Smurf attack exploits the target by sending repeated ping request to broadcast address of the target network. The ping request packet often uses forged IP address (return address), which is the target site that is to receive the denial of service attack. The result will be lots of ping replies flooding back to the innocent, spoofed host. If number of hosts replying to the ping request is large enough, the network will no longer be able to receive real traffic.

SYN Floods :-
When establishing a session between TCP client and server, a hand-shaking message exchange occurs betwen a server and client. A session setup packet contains a SYN field that identifies the sequence in the message exchange. An attacker may send a flood of connection request and do not respond to the replies, which leaves the request packets in the buffer so that legitimate connection request can’t be accommodated.

Teardrop Attack :-
Teardrop attack exploits by sending IP fragment packets that are difficult to reassemble. A fragment packet identifies an offset that is used to assemble the entire packet to be reassembled by the receiving system. In the teardrop attack, the attacker’s IP puts a confusing offset value in the sebsequent fragments and if the receiving system doesn’t know how to handle such situation, it may cause the system to crash.

Prevetion:-

1. Install Intrusion Detection System (IDS)
2. Implement Sysctl. Prevent ping attacks (ping of death, ping of flood, and smurf attacks) by disabling ping responses on the network machines. Enable IP Spoofing protection, and TCP SYN Cookie Protection.
3. Install advanced firewall and DDoS utilities.
4. Install Apache mod_evasive and mod_security modules to protect against HTTP DDoS attacks.

Mod_security:-
Since DDOS normally targets HTTP. Its always good to have a filtering system for apache . So that the request gets analyzed before web server handles it.

Mod_evasive:-
Detection is performed by creating an internal dynamic hash table of IP Addresses and URIs, and denying any single IP address from any of the following:

1. Requesting the same page more than a few times per second
2. Making more than 50 concurrent requests on the same child per second
3. Making any requests while temporarily blacklisted (on a blocking list)

Note:-
1. Well there are no 100% prevention or protection against DDOS.
2. This steps won’t be enough if the DDOS attack is of very high volume.

How dns works

A DNS client “resolves” an IP address by sending a specially formatted request to a DNS server. The client has to know the address of one or more DNS servers in advance. The reply from the server may be a direct reply with the IP address associated with the hostname, a referral to another DNS server, or a response indicating the requested name can’t be found in DNS.

Typically, the request will ask the server to “recursive“, i.e. if it cannot answer the question from its own local memory, it should go ask other servers on behalf of the client. This behavior helps the local server build up its own cache of addresses frequently looked up.

Another form of query is called iterative query, where a client machine sends the request to a known DNS server , if that DNS server fail to resolve the domain name into a IP, then the client sends the request to another DNS and this process goes on and on until it get the required IP resolution by sending address resolution request to all its known DNS.If every known DNS fail to give the IP, then client goes to the root domain.

When you type a URL into your browser, it uses the following steps to locate the correct website:

A DNS client uses a resolver to request resolution of a host name to an IP address. The resolver is really just a special-purpose application that’s sole function is to act as an intermediary between name servers and various applications that need name resolution, such as Web browsers, e-mail applications, and so on. Here’s an example: Assume you fire up your browser and direct it to connect to www.mysite.com.

1. Your browser checks it’s cache (memory) to see if it knows which IP address the domain name resolves to. If it knows, it will resolve it and display the web page.
2. If the domain name is unable to be resolved, the browser will check your hosts file for a DNS entry.
3. If there’s no entry in the hosts file, the browser will check the default DNS server (specified via your computer’s network settings, /etc/resolv.conf). This is usually your ISP’s DNS server or your employer’s. If the default DNS server has an entry for that domain name, the browser will display the applicable website.
4. If the default name server has no cached results, it sends a DNS query to the root server for the .com domain.
5. The root server responds with the addresses of the name servers that are authoritative for the mysite.com domain.
6. Your ISP’s name server then builds another request for www.mysite.com and submits it to mysite.com’s name server, which responds with the IP address of www.mysite.com.
7. That information is passed back to your resolver, which passes it to your application.

Verify PHP/cURL is working correctly

Simply, cURL is a command line tool for getting or sending files using URL syntax. It supports a range of common Internet protocols, including HTTP, FTP, SCP, SFTP, TFTP, TELNET, FILE, IMAP, POP3, SMTP and RTSP, etc. The command is designed to work without user interaction.

Usage:-

Basic use of cURL involves simply typing curl at the command line, followed by the URL of the output to retrieve.
To retrieve the google.com homepage, type:
curl www.google.com
What is PHP/CURL?
The module for PHP that makes it possible for PHP programs to access curl-functions from within PHP.

How to verify cURL is working correctly?.

cURL does have very powerfull functions which inturn not used properly may leads to complete breakdown of your server. Because of this most of the hosting companies disable some of these dangerous functions. But for a PHP Programmer cURL is an essential tool and must requires basic functionality atleast. It is very easy to check the PHP/cURL is working normal.

Steps:-

1. Create a php file “check_cURL.php” with following content using any of your favourite editor.

<?php
/**
* Initialize the cURL session
*/
$ch = curl_init();
/**
* Set the URL of the page or file to download.
*/
curl_setopt($ch, CURLOPT_URL,
‘http://news.google.com/news?hl=en&topic=t&output=rss’);
/**
* Create a new file
*/
$fp = fopen(‘rss.xml’, ‘w’);
/**
* Ask cURL to write the contents to a file
*/
curl_setopt($ch, CURLOPT_FILE, $fp);
/**
* Execute the cURL session
*/
curl_exec ($ch);
/**
* Close cURL session and file
*/
curl_close ($ch);
fclose($fp);
?>


2.  Execute the “check_cURL.php” script (I just run “php -q   check_cURL.php” from the terminal)

3.  Check the output file “rss.xml”. If the file contains data, we can conclude curl is working fine.

How does this script works:-

The check_cURL.php is simple php script which when called connects to the url specified(Google in our example) and download its source code. The script then writes its output to downloaded content to the output file(rss.xml in our example).

Custom php.ini per domain in Plesk Windows server

There will always be the scenarios where we need to set some special php settings for a particular domain or for a particular directory. This can be easily done in a Linux server, but with Windows it is always issues. But we can done this windows servers also and tell you what i have verified this by myself.

Prerequisites:-

*Custom php,ini file only works with php handler as “cgi” and not with “fastcgi” nor with ISAPI extension. So you need to verify this before you proceed further.

Follow the below steps to set the correct php mode.

1. Log in to your Hosting Control Panel
2. Select your domain name
3. Under “Web Site” tab, click on “Web Hosting Settings”
4. Under “PHP Support”, select your desired “PHP Mode” settings(cgi mode)
5. Hit the “Ok” button to activate.

Assumptions:-

  • The default location of php.ini for PHP5 is the PleskPHP5 base directory %plesk_dir%AdditionalPleskPHP5 (Eg: c:Program FilesParallelsPleskAdditionalPleskPHP5). If you place an PHP info page, you can easily find out from where the current php settings is loaded.
  • The document root of the domain “maindomain.com” is “d:Inetpubvhostsmaindomain.comhttpdocs”. Please note that this may be different in your hosting environment.
  • The server I am working on is a x86 based server.
  • Plesk version is 10.3.1, but it should work with others also.

Turn off the register_globals

I will explain the procedures with an example to turn off the register globals . There are two ways to configure php values for a particular domain:-

1. By placing an customized php.ini page on the corresponding directory or in domain.
2. By creating a Windows registry value for the particular php settings.
Placing an customized php.ini page on the corresponding directory
You need to place the php.ini file in “maindomain.com/httpdocs” directory or if you want to apply the only to a addon domain or a directory, then use the directory “maindomain.com/httpdocs/addondomain.com”.

Follow the below steps:-

1. Copy the PHP version 5 (php.ini-recommended or php.ini) ini file from the PHP location %plesk_dir%\AdditionalPleskPHP5 to the location “maindomain.com/httpdocs”
2. Rename the copied file to the exact name as ‘php-cgi-fcgi.ini‘. This is the most important step and won’t work otherwise.
3. You can make the changes needed to the above ini file, say set the “register_globals = Off”.
3. Create a php info page the corresponding directory and verify it is loading the correct “php.ini” (check the loaded configuration file section). Also verify whether the value you have changed is now updated under the ‘PHP info’ page.

This should do the work. If this method doesn’t work for you, here is the second method.

Creating a Windows registry value

Even though this is a simple procedure, i do not recommend anyone to edit the Windows Registry because if you screw up anything with Registry, you will also screwed up 🙂

When running PHP on Windows, the configuration values can be modified on a per-directory basis using the Windows registry. The configuration values are stored in the registry key HKLMSOFTWAREPHP5Per Directory Values, in the sub-keys corresponding to the path names. For example, configuration values for the directory c:inetpubwwwroot would be stored in the key HKLMSOFTWAREPHP5Per Directory Valuescinetpubwwwroot. The settings for the directory would be active for any script running from this directory or any subdirectory of it. The values under the key should have the name of the PHP configuration directive and the string value.

Simply, you can only add individual php configuration value inside of php.ini through the registry, which means that you have to set up keys to the file path ( where the client’s hosting folder located ) and then add a string value, string name will be the php.ini configuration name and value will be how you want it to be. So for setting register_globals to off for the maindomain.com, you have to setup keys to the path “HKEY_LOCAL_MACHINE > SOFTWARE > Wow6432Node > PHP > Per Directory Values > C > Inetpub > vhosts > maindomain.com > httpdocs” and then add a string value, string name will be “register_globals” and value will be 0 to put register_globals= off.
Note:

For 32 bit Windows registry path is ,  HKLMSOFTWAREPHP5Per Directory Values
For x64 based Windows registry path is,  HKEY_LOCAL_MACHINESOFTWAREWow6432NodePHP5Per Directory Values

Reference:-

http://forum.parallels.com

http://www.php.net

Powered by WordPress & Theme by Anders Norén