A firewall is a hardware or software installed to provide security to the private networks connected to the internet. They can be implemented in both hardware and software, or a combination of both. All data entering or leaving the Intranet passes through the firewall which allows only the data meeting the administrators’ rules to pass through it.

1. Packet Filtering Firewall: This type of Firewall detects packets and block unnecessary packets and makes network traffic release.
2. Screening Router Firewalls: It's a software base firewall available in Router provides only light filtering.
3. Computer-based Firewall : It's a firewall stored in server with an existing Operating System like Windows and UNIX.
4. Hardware base Firewall: Its device like box allows strong security from public network. Mostly used by big networks.
5. Proxy Server: Proxy server allows all clients to access Internet with different access limits. Proxy server has its own firewall which filters the all packet from web server.

CISCO pix firewall security is stateful firewall. It uses ASA Technology.

Firewalls can't protect against attacks that don't go through the firewall. Many corporations that connect to the Internet are very concerned about proprietary data leaking out of the company through that route. Unfortunately for those concerned, a magnetic tape can just as effectively be used to export data. Many organizations that are terrified (at a management level) of Internet connections have no coherent policy about how dial-in access via modems should be protected.

IPSEC (IP Security) refers to a set of standards developed by the Internet Engineering Task Force (IETF). There are many documents that collectively define what is known as ``IPSEC'' [4]. IPSEC solves two problems which have plagued the IP protocol suite for years: host-to-host authentication (which will let hosts know that they're talking to the hosts they think they are) and encryption (which will prevent attackers from being able to watch the traffic going between machines).