Abstract: Network security is highly needed to protect legitimate files from unauthorized access, misuse, modification, destruction or improper disclosure. Recent activities in the field of cyber world proves that network attacks can cause huge amount of loss to governments, private enterprises and the general public in terms of money, data confidentiality and reputation. There always occurs a collision between the security specialists and the attackers frequently. In this study, we present an overview of different types of network vulnerabilities and brief discussion about preventive measures from such attacks including classification of IDS and IPS.