Anyone that knows Linux, knows that this operating system, enables so many solutions, and they are part of the Linux operating system package. You can gain almost any type of services you need, by either using the built in services on the operating system after the installation (which means they are coming installed within the OS) or by doing a simple update/download and install of new services which are not built in, It is as simple as that.

I will give some examples from the UBUNTU Linux operating system, which is one of my favorite, and it is very simple to use. Installing a service is almost made by using one simple command – called APT-GET (This command goes to find the service you need, download it, and installs it on your Linux system. Mostly it means the service will be installed and running on the system. Sometimes you might need to edit some configuration files, in order to fit it into your network definitions.

The most important issue that you need to remember is that Linux enables you to do anything you want. Linux is being used by many and some prefer to use it and not use the Microsoft Windows Operating System which is so common.

Linux has many operating systems, some are server based (no graphical interface needed) and some are suitable for client side computers/laptops, they do include X-windows which is the graphic interface of a Linux based operating system. Linux has many different graphical interface distributions, which actually means that those distributions are actually a fully functional operating system, with the needed packages of services. Each Linux distribution include different packages, and different GUI interface (which means the graphical side looks a bit different).

The base of them usually works the same, but some of them are based on different Linux Kernel, so the commands are a bit different, and needs to get used to. That is usually why most Linux users get to know one type of a Linux kernel that they get along best with and they stick to that OS and Linux Kernel, on their future Linux experiences.

So let go over some examples of what you can do with the Linux operating system, and how simple things are when defining new services to the system.

Linux Firewall:

Linux has a built in mechanism called IPTABLES, this is a port filtering mechanism, that enables you to set rules for what can pass through the system and what can’t. Firewall rules are mostly port based, any service has its own port, and by defining which ports are allowed and which are not, you can create your own firewall based on that built-in mechanism. All you will need is to place two network card on your Linux, and let the traffic pass through the Linux machine, as it controls the rules of passage. When IPTABLES is empty and no rules are applied, it means anything can go through from outside in, and from the inside out. This option is mostly used by the Linux Server systems.

* Article on how to set a simple Linux Firewall

Another option if you want a graphical management console to define the firewall:

For Linux Desktop – that includes X-Windows (a Graphic interface), you can use the FWBUILDER (Firewall Builder). This tool enables a graphic management interface, that enables you to define the firewall rules, like the tools used on firewall routers (like the CISCO PIX).

* Using fwbuilder to create a Linux firewall

Linux web server:

The Linux web server is mostly based on the APACHE service. Since most application use PHP, and databases, you can use the MYSQL, and of course PHP, so you need to install them as well, and some other tools that can assist you. Below are the basic tools you will need to create a full functional web server, which includes all of the needed services.

• Apache 2 – Linux Web server
• MySQL 5 – MySQL Database Server
• PHP4/5 – PHP Scripting Language
• phpMyAdmin – Web-based database admin software.
• Webalizer – Website Traffic Analyzer
• Mail Server – Postfix (MTA) with Dovecot IMAP/POP3 + Sasl Authentication
• Squirrelmail – A web based email
• VSFTP – A fast ftp server to upload files
• Webmin – A freely available server control panel
• ClamAV – Antivirus software.
• A Firewall using IPtables.

* Build Your Own Web Server

So to summarize, you can do whatever you want to with Linux, just search the internet and see how easy it is.

Active Directory is a package designed by Microsoft to manage an organizational network, this package is using different tools to organize and manage the corporate network. Basically before we get into specifics, the Active Directory is creating a managerial environment, where all of the network clients (end users) are connected to it, and anyone who connects to it is registered and monitored by the Active Directory system. That enables it, to manage the end users, what they are allowed to do, what they can’t, which resources will be available to whom. It creates groups and give those groups policies (group of rules) which binds that group into those rules, and every end user that is defined within this group is bind by it rules, and accordingly can or can’t do things within the network.

The Active Directory, has been built inside the windows servers (server 2003, 2008) and the Active Directory is it’s source of organization. Anyone who connects to the server is actually connected to the Active Directory, and through that can use the network resources, as defined in the Active Directory rules.

So how does it work ?
The tools that Active Directory uses, are the LDAP (lightweight directory access protocol) which is basically a library service. There is the authentication protocol based on Kerberos (authentication protocol for client/server services that enables connection and communication using secret encrypted codes over the internet), then there is the DNS (domain name system, which translate names like website addresses into IP addresses) and finally the group enforcement, making sure the group rules are working properly.

The Active Directory has a Physical aspect which includes a database that is residing on DC (DomainControllers), those DCs can do various operations and purposes, or the same operation for redundancy and loading performance and separations, where each change in domain is replicated using a replication mechanism, to the other domains and of course updating the whole organization accordingly. The Logical aspect of it is hierarchical concepts, like a pyramid, the higher structure is a forest, which is containing trees which resemble a collection of DCs. The forest is actually any object on the network, anything connected to it, and the rules apply using that hierarchy.

Each object on the network is an “Entity” and each entity has its own definitions which divides into 3 types: resources, services & users. Every object has it’s unique GUID (ID), which identifies against the library (the LDAP) and that is how it gets identified.

This is the basic operation of the Active Directory. It’s use and functionality is to centralize manage all of the computerized resources in the organization. The policy can be implemented using a management tool called GPO (group policy) which can manage the policies given to different groups in the organization’s network.

This whole concept enable the network administrator to obtain control over the whole network from one computer (DC) and  to define what type of desktop will a user have, which directories he can access, what tools he can use etc…