Referencias:

1. Firewall toolkit overview de Trusted Information System Inc. disponible en: http://www.tis.com/docs/products/fwtk/fwtkoverview.html
2. The TIS firewall Toolkit FAQ disponible en: http//www.erols.com/avenger/
3. Building Internet Firewalls D.Brent Chapman and Elizabeth D.Zwicky Ed O´Reilly & Associates, Inc