Firewalls
After several security related internet newsgroups started overflowing with posts it becomes clear something hand to done to help secure networks. The first firewalls were implemented in routers between different segment s of the network. These firewalls were basically ACLs in routers.
Slowly firewall technology started to evolve. Early firewall technology known as packet filtering was not enough to stop the constant attacks. The firewall had to more intelligent and understand the different protocols.