Computer networks in academic environments could have many secUlity problems if there weren't enough precaution. The source of these problems is generally vulnerabilities of TCP/IP protocol and Internet. Vulnerabilities can cause threats. These threats will be analyzed in this thesis. There are many kind of countelmeasures to prevent the assets of the academic networks. Firewalls are a kind of countermeasure against these attacks. In this thesis, these countelmeasures will be also analyzed and a firewall will be designed and proposed for academic environments against these threats.