Cisco IOS Firewall

Abstract

The Cisco IOS Firewall, provides robust, integrated firewall and intrusion detection functionality for every perimeter of the network. Available for a wide range of Cisco IOS software-based routers, the Cisco IOS Firewall offers sophisticated security and policy enforcement for connections within an organization (intranet) and between partner networks (extranets), as well as for securing Internet connectivity for remote and branch offices.

A security-specific, value-add option for Cisco IOS Software, the Cisco IOS Firewall enhances existing Cisco IOS security capabilities, such as authentication, encryption, and failover, with state-of-the-art security features, such as stateful, application-based filtering (context-based access control), defense against network attacks, per user authentication and authorization, and real-time alerts.
The Cisco IOS Firewall is configurable via Cisco ConfigMaker software, an easy-to-use Microsoft Windows 95, 98, NT 4.0 based software tool.
A Firewall is a network security device that ensures that all communications attempting to cross it meet an organization's security policy. Firewalls track and control communications deciding whether to allow ,reject or encrypt communications.Firewalls are used to connect a corporate local network to the Internet and also within networks. In other words they stand in between the trusted network and the untrusted network.
The first and most important decision reflects the policy of how your company or organization wants to operate the system. Is the firewall in place to explicitly deny all services except those critical to the mission of connecting to the net, or is the firewall is in place to provide a metered and audited method of 'Queuing' access in a non-threatening manner. The second is what level of monitoring, reducing and control do you want? Having established the acceptable risk level you can form a checklist of what should be monitored, permitted and denied. The third issue is financial.
Implementation methods
Two basic methods to implement a firewall are

1.As a Screening Router:

A screening router is a special computer or an electronic device that screens (filters out) specific packets based on the criteria that is defined. Almost all current screening routers operate in the following manner.
a. Packet Filter criteria must be stored for the ports of the packet filter device. The packet filter criteria are called packet filter ruler.

b. When the packets arrive at the port, the packet header is parsed. Most packet filters examine the fields in only the IP, TCP and UDP headers.
c. The packet filter rules are stored in a specific order. Each rule is applied to the packet in the order in which the packet filter is stored.
d. If the rule blocks the transmission or reception of a packet the packet is not allowed.
e. If the rule allows the transmission or reception of a packet the packet is allowed.
f. If a packet does not satisfy any rule it is blocked.