Que es un Firewall (Cortafuego)










Un cortafuegos (o firewall en inglés), es un elemento de hardware o software utilizado en las redes para prevenir algunos tipos de comunicaciones prohibidas por las políticas de red, las cuales se fundamentan en las necesidades del usuario.Forman una barrera para proteger a los ordenadores conectados a Internet en las dos direcciones: evitan una intrusión al PC desde la Red e impiden que los programas instalados accedan a Internet sin permiso.
Su objetivo es prevenir ataques a las redes (sea Internet o la intranet de una empresa) y para lograrlo emplean distintos medios.



Tipos de cortafuegos
Los cortafuegos tradicionales son de hardware, es decir, un dispositivo específico instalado en una red para levantar una defensa y proteger a la red del exterior. Son los utilizados en entorno profesionales: el administrador de red define una serie de reglas para permitir el acceso y detiene los intentos de conexión no permitidos.
Los cortafuegos personales son programas que filtran el tráfico que entra y sale de una computadora. Una vez instalados, el usuario debe definir el nivel de seguridad: permite o deniega el acceso de determinados programas a Internet (de forma temporal o definitiva) y autoriza o no los accesos desde el exterior.
Sus ventajas mas notorias:



Protege de intrusiones.- Solamente entran a la red las personas autorizadas basadas en la política de la red en base a las configuraciones.


Optimización de acceso.


- Identifica los elementos de la red internos y optimiza que la comunicación entre ellos sea más directa si así se desea. Esto ayuda a reconfigurar rápida y fácilmente los parámetros de seguridad.Protección de información privada.


- Permite el acceso solamente a quien tenga privilegios a la información de cierta área o sector de la red.Protección contra virus.


- Evita que la red se vea infestada por nuevos virus que sean liberados.
Aunque el usuario medio pueda creer que eso de los ataques no es algo que le pueda suceder en su casa a su computadora, el cortafuegos se convierte un elemento imprescindible si se utiliza mucho el ordenador y se está conectado permanentemente mediante ADSL o cable. El firewall evitará la entrada de los programas que rastrean direcciones IP (un número que se asigna cada ordenador conectado) a la caza de conexiones por banda ancha que parasitar, a la vez que frustrará los intentos de los programas espía de robar datos del PC y de los troyanos de abrir brechas de seguridad.
La configuración correcta de cortafuegos se basa en conocimientos considerables de los protocolos de red y de la seguridad de la computadora. Errores pequeños pueden dejar a un cortafuego sin valor como herramienta de seguridad.
En Internet se pueden encontrar versiones no profesionales de cortafuegos, suficientes para el usuario doméstico, que se pueden descargar de forma gratuita. El más popular es
ZoneAlarm, aunque existen otros como Outpost, Kerio o Sygate.
También hay cortafuegos integrados en los programas antivirus o en el propio sistema operativo. El que viene con Windows XP no es demasiado seguro porque, al contrario que otros cortafuegos, sólo vigila las conexiones entrantes, mientras que el tráfico de salida no está restringido.
Los cortafuegos, por defecto, se activan siempre que se enciende el ordenador. Hay que configurarlo con cuidado, pues puede ocurrir que no funcione el correo electrónico o no se abran páginas web en el navegador porque el ‘firewall’ no permite a estos programas acceder a Internet.
Para eso concentran todo el flujo entrante y saliente entre la PC e Internet y bloquea los pedidos de enlaces no solicitados por el usuario potencialmente inseguros, instalaciones clandestinas de programas y algunos hasta bloquean pop ups, publicidades, etc.



Como funcionan los FirewallSe





manejan por zonas (seguras o no) o bien por niveles de seguridad, los que establece el usuario según el grado de permisividad que le imponga al equipo. Pero luego el programa se va configurando con el tiempo. Como decimos en cada review, en realidad con los Firewalls no hay que hacer nada, sólo configurarlos según las necesidades o gustos del usuario, cosa que no termina con la instalación.
Tras esta, una vez que el usuario se conecta a Internet (o aún antes) comienza a trabajar el programa. Los primeros días de uso pueden ser un tanto engorrosos ya que tanto el usuario como el programa “aprenden” mutuamente. El usuario aprende las funciones y el programa qué cosas debe dejar pasar, qué bloquear y qué programas dejar conectar, por eso al principio son puras preguntas, hasta que se van conformando las reglas de uso en la medida que el usuario haga determinadas acciones con las alarmas que pueden ser de varios tipos. Con este tipo de aviso el programa pide que se defina la regla que se va a aplicar entre alguna de las posibles.Una vez que se determina qué hacer con esa acción (por ejemplo permitir que un programa se conecte siempre a Internet), con cada cartel de alerta se van configurando las reglas ya que luego ese aviso no va a volver a aparecer. Con el tiempo estos avisos se reducen al mínimo.Por cada acción crean un registro de la actividad (log) para el posterior análisis del usuario.



Tipos de peligros que puede evitar un firewall





-Instalación y ejecución de programas instalados clandestinamente desde Internet, por ejemplo vía aplicaciones ActiveX o Java que pueden llegar a transferir datos personales del usuario a sitios.
-Acceso de terceros por fallas o errores de configuración de Windows (por ejemplo de NetBIOS).
-Instalación de publicidad (advertisers) o elementos de seguimiento (track) como las cookies.
-Troyanos: aplicaciones ocultas que se descargan de la red y que pueden ser usadas por terceros para extraer datos personales. A diferencia del virus, estos troyanos son activados en forma remota por un tercero.
-Reducción del ancho de banda disponible por el tráfico de banners, pop us, sitios no solicitados, y otro tipo de datos innecesarios que ralentizan la conexión.
-Spyware
-Utilización de la línea telefónica por terceros por medio de Dialers (programas que cortan la actual conexión y utilizan la línea para llamadas de larga distancia)

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