In the past, we were often taught that we should have at least two layers of firewalls and it was best to use different brands so that at least it would make it more difficult for hackers to penetrate. This is not an issue, but I am mostly seeking comments on such a firewall design in today's context. Firewalls are not the targets anymore, so is it still relevant that we need to have at least two layers and using different brands? Further, the firewalls nowadays come with more features such as application layer protection etc.
I tend to subscribe to the idea of using one layer but placing more emphasis on the configurations and make sure there is 100% no misconfigurations in the firewall rules, plus making full use of the features that comes with next generation firewalls. There is actually no need for two layers?