Firewalls

Not a day goes by that I don’t have a firewall conversation with somebody. There is a general assumption that once you install a firewall your network/servers behind it are secure. Firewalls aren’t a magic cure for security holes.
A firewall limits what traffic is allowed to traverse its interfaces, if you have a vulnerable system behind a firewall that you are allowing traffic to the firewall won’t do anything for you.
I firewall is only one of a series of steps that you have to take to protect your network. I found this slide funny, I hope you do to.