How to Configure Squid Proxy Server for URL Rewriting

URL rewriting is a technique used to alter or modify the parameters in a URL. This can be particularly useful in a variety of scenarios such as redirecting users, blocking access to certain URLs, or even load balancing.

Squid, a highly versatile proxy server, supports URL rewriting through the use of external redirector programs. This allows Squid to pass URLs to an external program which then returns the rewritten URL back to Squid.

In this tutorial, we will guide you through the process of setting up URL rewriting on a Squid proxy server.

Before we begin, it’s important to note that this tutorial assumes you already have a working Squid proxy server. If you don’t, you can refer to our previous tutorial on setting up a Squid proxy server on CentOS and Ubuntu.

Step 1: Install URL Rewriting Software

The first step in configuring Squid for URL rewriting is to install a URL rewriting software. There are several options available, but for this tutorial, we will use SquidGuard, a free, open-source URL redirector software.

yum install squidGuard -y

Step 2: Configure SquidGuard

After installing SquidGuard, the next step is to configure it. The configuration file for SquidGuard is located at /etc/squid/squidGuard.conf.

nano /etc/squid/squidGuard.conf

In this file, you can define your URL rewriting rules. For example, to block access to a specific website, you can add the following lines:

acl {
  badsites {
    domainlist /etc/squid/badsites
  }
}

In this example, /etc/squid/badsites is a file that contains a list of websites to block.

More examples below.

Step 3: Configure Squid to Use SquidGuard

After configuring SquidGuard, the next step is to configure Squid to use SquidGuard for URL rewriting. This can be done by adding the following line to the Squid configuration file located at /etc/squid/squid.conf:

url_rewrite_program /usr/bin/squidGuard

This tells Squid to use SquidGuard as the URL rewriting program.

Step 4: Restart Squid

After making the necessary changes, the final step is to restart Squid for the changes to take effect.

systemctl restart squid

Congratulations! You have successfully configured Squid for URL rewriting. Now, whenever a user tries to access a URL that matches one of your rewriting rules, Squid will rewrite the URL as specified.

URL Rewriting Examples

SquidGuard is a powerful URL redirector and rewriter used in conjunction with Squid Proxy Server. Here are five examples of how SquidGuard can be used:

1. Blocking Specific Websites

You can use SquidGuard to block access to specific websites. For example, if you want to block access to social media sites like Facebook and Twitter, you can add these domains to a blacklist and configure SquidGuard to block all URLs from these domains.

acl {
  social_networks {
    domainlist /etc/squid/blacklists/social_networks
  }
}

2. Redirecting URLs

SquidGuard can also be used to redirect URLs. For example, you can redirect all requests to an old domain to a new one.

rewrite oldsite {
  s@http://oldsite.com@http://newsite.com@i
}

3. Implementing Time-Based Rules

With SquidGuard, you can implement time-based rules. For instance, you can block access to certain websites during working hours.

time workhours {
  weekly mtwhf 08:00 - 17:00
}

acl {
  work {
    pass !social_networks within workhours
    redirect http://localhost/blocked.html
  }
}

4. Blocking Specific File Types

You can use SquidGuard to block specific file types. For example, you can block all .exe files to prevent users from downloading potentially harmful executable files.

acl {
  exe_files {
    urllist /etc/squid/blacklists/exe_files
  }
}

5. Implementing Different Rules for Different Users

SquidGuard allows you to implement different rules for different users. For example, you can block social media sites for employees but allow access for the marketing team.

src employees {
  ip 192.168.1.0/24
  !ip 192.168.1.10
}

src marketing {
  ip 192.168.1.10
}

acl {
  employees {
    pass !social_networks all
  }
  marketing {
    pass all
  }
}

6. Blocking Access to Adult Content

SquidGuard can be used to block access to adult content. You can do this by using a precompiled blacklist of adult content websites and configuring SquidGuard to block all URLs from these domains.

acl {
  adult_content {
    domainlist /etc/squid/blacklists/adult_content
  }
}

7. Redirecting HTTP to HTTPS

You can use SquidGuard to redirect all HTTP traffic to HTTPS, ensuring that all connections are secure.

rewrite http_to_https {
  s@http://@https://@i
}

8. Implementing a Whitelist

Instead of blocking specific sites, you can use SquidGuard to allow only specific sites. This is known as a whitelist. You can create a list of allowed domains and configure SquidGuard to block all URLs not on this list.

acl {
  whitelist {
    pass domainlist /etc/squid/whitelists/allowed_sites
    redirect http://localhost/blocked.html
  }
}

9. Blocking Access Based on User Agent

SquidGuard can also block access based on the user agent. For example, you can block all requests from bots or web crawlers.

acl {
  bots {
    useragentlist /etc/squid/blacklists/bots
  }
}

10. Redirecting to a Maintenance Page

If your site is down for maintenance, you can use SquidGuard to redirect all requests to a maintenance page.

rewrite maintenance {
  s@http://yoursite.com@http://yoursite.com/maintenance.html@i
}

Remember, URL rewriting is a powerful tool, but with great power comes great responsibility. Always ensure that your rewriting rules are accurate and serve a legitimate purpose. Misconfigured rewriting rules can lead to unexpected behavior and potential security risks.

Commands Mentioned:

• yum install squidGuard -y – This command installs SquidGuard on your server. SquidGuard is a URL redirector used in conjunction with Squid to provide URL rewriting capabilities.
• nano /etc/squid/squidGuard.conf – This command opens the SquidGuard configuration file in a text editor. This is where you define your URL rewriting rules.
• systemctl restart squid – This command restarts the Squid service. This is necessary for any changes you make to the Squid or SquidGuard configuration files to take effect.

Conclusion

In this guide, we have walked you through the process of setting up URL rewriting on a Squid proxy server using SquidGuard. We started with the installation of SquidGuard, moved on to its configuration, and then integrated it with Squid.

URL rewriting is a powerful feature that can greatly enhance the functionality of your Squid proxy server. It allows you to control and manipulate the URLs that pass through your proxy server, enabling you to redirect users, block access to certain URLs, or even perform load balancing. However, it’s important to use this feature responsibly, as misconfigured rewriting rules can lead to unexpected behavior and potential security risks.

For more information on proxy servers and web servers, you can check out our guides on the best proxy servers, and the best web servers.

Remember, the key to a secure and efficient network is continuous learning and experimentation.

Hope you found this tutorial helpful.

If you have any questions or run into any issues, feel free to leave a comment.

FAQ

1. Can I use SquidGuard without Squid?

   No, SquidGuard is a plugin for Squid. It is designed to work in conjunction with Squid to provide URL rewriting and redirecting capabilities. Without Squid, SquidGuard cannot function.

2. Can SquidGuard block specific file types?

   Yes, SquidGuard can block specific file types. This is done by creating a blacklist of the file extensions you want to block and configuring SquidGuard to block all URLs that end with these extensions.

3. Can I use SquidGuard to implement time-based rules?

   Yes, SquidGuard allows you to implement time-based rules. This can be useful for blocking access to certain websites during specific times, such as during working hours.

4. Can SquidGuard redirect URLs?

   Yes, SquidGuard can redirect URLs. This is done by creating rewrite rules in the SquidGuard configuration file. These rules specify the original URL and the URL to which it should be redirected.

5. Can I use SquidGuard to implement different rules for different users?

   Yes, SquidGuard allows you to implement different rules for different users or groups of users. This is done by defining different source groups in the SquidGuard configuration file and specifying different access control lists for each group.