| network security -
January 20th, 2009
Network Security
Network
A ``network'' has been defined as ``any set of interlinking lines resembling a net, a network of roads || an interconnected system, a network of alliances.''
Firewalls
In order to provide some level of separation between an organization's intranet and the Internet, firewalls have been employed. A firewall is simply a group of components that collectively form a barrier between two networks.
Bastion host.
A general-purpose computer used to control access between the internal (private) network (intranet) and the Internet (or any other untrusted network).
Router.
A special purpose computer for connecting networks together.
Access Control List (ACL).
Many routers now have the ability to selectively perform their duties, based on a number of facts about a packet that comes to it. This includes things like origination address, destination address, destination service port, and so on
Demilitarized Zone (DMZ).
The DMZ is a critical part of a firewall: it is a network that is neither part of the untrusted network, nor part of the trusted network. But, this is a network that connects the untrusted to the trusted.
Proxy.
This is the process of having one host act in behalf of another. A host that has the ability to fetch documents from the Internet might be configured as a proxy server
Types of Firewalls
1. Application Gateways
These are made up of bastion hosts that run special software to act as a proxy server. This software runs at the Application Layer of our old friend the ISO/OSI Reference Model, hence the name. Clients behind the firewall must be proxitized (that is, must know how to use the proxy, and be configured to do so) in order to use Internet services. Traditionally, these have been the most secure, because they don't allow anything to pass by default, but need to have the programs written and turned on in order to begin passing traffic.
2. Packet Filtering
Packet filtering is a technique whereby routers have ACLs (Access Control Lists) turned on. By default, a router will pass all traffic sent it, and will do so without any sort of restrictions. Employing ACLs is a method for enforcing your security policy with regard to what sorts of access you allow the outside world to have to your internal network, and vice versa.
3. Hybrid Systems
In an attempt to marry the security of the application layer gateways with the flexibility and speed of packet filtering, some vendors have created systems that use the principles of both.
IT GOVERNANCE
Definition
The leadership and organisational structures and processes that ensure that the organisation’s IT sustains and extends the organisation’s strategies and objectives.'
Information technology governance, IT governance or ICT Governance, is a subset discipline of Corporate governance focused on information technology systems and their performance and risk management. The rising interest in IT governance is partly due to compliance initiatives as well as the acknowledgement that IT projects can easily get out of control and profoundly affect the performance of an organization.
A characteristic theme of IT governance discussions is that the IT capability can no longer be a black box. The traditional handling of IT management by board-level executives is that due to limited technical experience and IT complexity, key decisions are deferred to IT professionals. IT governance implies a system in which all stakeholders, including the board, internal customers and related areas such as finance, have the necessary input into the decision making process. This prevents a single stakeholder, typically IT, being blamed for poor decisions. It also prevents users from later complaining that the system does not behave or perform as expected.
IT is essential to manage transactions, information and knowledge necessary to initiate and sustain economic and social activities. These activities increasingly rely on globally cooperating entities to be successful. In many organizations, IT is fundamental to support, sustain and grow the business.
While many organizations recognize the potential benefits that technology can yield, the successful ones also understand and manage the risks associated with implementing new technologies. Among the enterprise's challenges and concerns are:
Aligning IT strategy with the business strategy
Cascading strategy and goals down into the enterprise
Providing organizational structures that facilitate the implementation of strategy and goals
Insisting that an IT control framework be adopted and implemented
Measuring IT's performance
Effective and timely measures aimed at addressing these top management concerns need to be promoted by the governance layer of an enterprise. Hence, boards and executive management need to extend governance, already exercised over the enterprise, to IT by way of an effective IT governance framework that addresses strategic alignment, performance measurement, risk management, value delivery and resource management. Simply put, IT governance and the effective application of an IT governance framework are the responsibilities of the board of directors and executive management. IT governance is an integral part of enterprise governance and consists of the leadership and organizational structures and processes that ensure that the organization's IT sustains and extends the organization's strategies and objectives. An IT governance framework, such as Control Objectives for Information and related Technology (COBIT) can be a critical element in ensuring proper control and governance over information and the systems that create, store, manipulate and retrieve it.
IT governance is supported by disciplines such as
• IT portfolio management
• Enterprise architecture
• Project governance
• Project management and Program management in the enterprise IT
• IT service management
• Business Technology Optimization
Integration Testing
• Top-down integration testing
1. Main control module used as a test driver and stubs are substitutes for components directly subordinate to it.
2. Subordinate stubs are replaced one at a time with real components (following the depth-first or breadth-first approach).
3. Tests are conducted as each component is integrated.
4. On completion of each set of tests and other stub is replaced with a real component.
5. Regression testing may be used to ensure that new errors not introduced.
• Bottom-up integration testing
1. Low level components are combined in clusters that perform a specific software function.
2. A driver (control program) is written to coordinate test case input and output.
3. The cluster is tested.
4. Drivers are removed and clusters are combined moving upward in the program structure.
• Regression testing (check for defects propagated to other modules by changes made to existing program)
1. Representative sample of existing test cases is used to exercise all software functions.
2. Additional test cases focusing software functions likely to be affected by the change.
3. Tests cases that focus on the changed software components.
• Smoke testing
1. Software components already translated into code are integrated into a build.
2. A series of tests designed to expose errors that will keep the build from performing its functions are created.
3. The build is integrated with the other builds and the entire product is smoke tested daily (either top-down or bottom integration may be used).
Debugging
• Debugging (removal of a defect) occurs as a consequence of successful testing.
• Some people are better at debugging than others.
• Common approaches:
1. Brute force (memory dumps and run-time traces are examined for clues to error causes)
2. Backtracking (source code is examined by looking backwards from symptom to potential causes of errors)
3. Cause elimination (uses binary partitioning to reduce the number of locations potential where errors can exist) | 
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