How to change IP address from the Windows command line

To do the same thing via the command line, use the netsh tool.

After some experimentation, I found that the following two commands were sufficient to give my machine a static IP address and have everything still work ok. The "interface ip set address" command changes the IP to 192.168.1.101 (this address is outside the range allocated by our DHCP server, therefore it will be different to what we had before) and I also had to provide the subnet mask (255.255.255.0), default gateway (192.168.1.5) and a gateway metric. The second command explicitly sets the DNS server to use for name resolution - normally this is done for us by the DHCP server.

netsh interface ip set address "Local Area Connection" static 192.168.1.101 255.255.255.0 192.168.1.5 1
netsh interface ip set dns "Local Area Connection" static 192.168.1.200 primary

To change the interface back to using DHCP and so have it allocated a different IP address

netsh interface ip set address "Local Area Connection" dhcp
netsh interface ip set dns "Local Area Connection" dhcp

Networking:Client/Server

Client/Server Software Architectures--An Overview

Purpose and Origin
The term client/server was first used in the 1980s in reference to personal computers (PCs) on a network. The actual client/server model started gaining acceptance in the late 1980s. The client/server software architecture is a versatile, message-based and modular infrastructure that is intended to improve usability, flexibility, interoperability, and scalability as compared to centralized, mainframe, time sharing computing.

A client is defined as a requester of services and a server is defined as the provider of services. A single machine can be both a client and a server depending on the software configuration. For details on client/server software architectures see Schussel and Edelstein [Schussel 96, Edelstein 94].

This technology description provides a summary of some common client/server architectures and, for completeness, also summarizes mainframe and file sharing architectures. Detailed descriptions for many of the individual architectures are provided elsewhere in the document.

Technical Detail
Mainframe architecture (not a client/server architecture). With mainframe software architectures all intelligence is within the central host computer. Users interact with the host through a terminal that captures keystrokes and sends that information to the host. Mainframe software architectures are not tied to a hardware platform. User interaction can be done using PCs and UNIX workstations. A limitation of mainframe software architectures is that they do not easily support graphical user interfaces (see Graphical User Interface Builders) or access to multiple databases from geographically dispersed sites. In the last few years, mainframes have found a new use as a server in distributed client/server architectures (see Client/Server Software Architectures) [Edelstein 94].

File sharing architecture (not a client/server architecture). The original PC networks were based on file sharing architectures, where the server downloads files from the shared location to the desktop environment. The requested user job is then run (including logic and data) in the desktop environment. File sharing architectures work if shared usage is low, update contention is low, and the volume of data to be transferred is low. In the 1990s, PC LAN (local area network) computing changed because the capacity of the file sharing was strained as the number of online user grew (it can only satisfy about 12 users simultaneously) and graphical user interfaces (GUIs) became popular (making mainframe and terminal displays appear out of date). PCs are now being used in client/server architectures [Schussel 96, Edelstein 94].

Client/server architecture. As a result of the limitations of file sharing architectures, the client/server architecture emerged. This approach introduced a database server to replace the file server. Using a relational database management system (DBMS), user queries could be answered directly. The client/server architecture reduced network traffic by providing a query response rather than total file transfer. It improves multi-user updating through a GUI front end to a shared database. In client/server architectures, Remote Procedure Calls (RPCs) or standard query language (SQL) statements are typically used to communicate between the client and server [Schussel 96, Edelstein 94].

The remainder of this write-up provides examples of client/server architectures.

Two tier architectures. With two tier client/server architectures (see Two Tier Software Architectures), the user system interface is usually located in the user's desktop environment and the database management services are usually in a server that is a more powerful machine that services many clients. Processing management is split between the user system interface environment and the database management server environment. The database management server provides stored procedures and triggers. There are a number of software vendors that provide tools to simplify development of applications for the two tier client/server architecture [Schussel 96, Edelstein 94].

The two tier client/server architecture is a good solution for distributed computing when work groups are defined as a dozen to 100 people interacting on a LAN simultaneously. It does have a number of limitations. When the number of users exceeds 100, performance begins to deteriorate. This limitation is a result of the server maintaining a connection via "keep-alive" messages with each client, even when no work is being done. A second limitation of the two tier architecture is that implementation of processing management services using vendor proprietary database procedures restricts flexibility and choice of DBMS for applications. Finally, current implementations of the two tier architecture provide limited flexibility in moving (repartitioning) program functionality from one server to another without manually regenerating procedural code. [Schussel 96, Edelstein 94].

Three tier architectures. The three tier architecture (see Three Tier Software Architectures) (also referred to as the multi-tier architecture) emerged to overcome the limitations of the two tier architecture. In the three tier architecture, a middle tier was added between the user system interface client environment and the database management server environment. There are a variety of ways of implementing this middle tier, such as transaction processing monitors, message servers, or application servers. The middle tier can perform queuing, application execution, and database staging. For example, if the middle tier provides queuing, the client can deliver its request to the middle layer and disengage because the middle tier will access the data and return the answer to the client. In addition the middle layer adds scheduling and prioritization for work in progress. The three tier client/server architecture has been shown to improve performance for groups with a large number of users (in the thousands) and improves flexibility when compared to the two tier approach. Flexibility in partitioning can be a simple as "dragging and dropping" application code modules onto different computers in some three tier architectures. A limitation with three tier architectures is that the development environment is reportedly more difficult to use than the visually-oriented development of two tier applications [Schussel 96, Edelstein 94]. Recently, mainframes have found a new use as servers in three tier architectures (see Mainframe Server Software Architectures).

Three tier architecture with transaction processing monitor technology. The most basic type of three tier architecture has a middle layer consisting of Transaction Processing (TP) monitor technology (see Transaction Processing Monitor Technology). The TP monitor technology is a type of message queuing, transaction scheduling, and prioritization service where the client connects to the TP monitor (middle tier) instead of the database server. The transaction is accepted by the monitor, which queues it and then takes responsibility for managing it to completion, thus freeing up the client. When the capability is provided by third party middleware vendors it is referred to as "TP Heavy" because it can service thousands of users. When it is embedded in the DBMS (and could be considered a two tier architecture), it is referred to as "TP Lite" because experience has shown performance degradation when over 100 clients are connected. TP monitor technology also provides

* the ability to update multiple different DBMSs in a single transaction
* connectivity to a variety of data sources including flat files, non-relational DBMS, and the mainframe
* the ability to attach priorities to transactions
* robust security

Using a three tier client/server architecture with TP monitor technology results in an environment that is considerably more scalable than a two tier architecture with direct client to server connection. For systems with thousands of users, TP monitor technology (not embedded in the DBMS) has been reported as one of the most effective solutions. A limitation to TP monitor technology is that the implementation code is usually written in a lower level language (such as COBOL), and not yet widely available in the popular visual toolsets [Schussel 96].

Three tier with message server. Messaging is another way to implement three tier architectures. Messages are prioritized and processed asynchronously. Messages consist of headers that contain priority information, and the address and identification number. The message server connects to the relational DBMS and other data sources. The difference between TP monitor technology and message server is that the message server architecture focuses on intelligent messages, whereas the TP Monitor environment has the intelligence in the monitor, and treats transactions as dumb data packets. Messaging systems are good solutions for wireless infrastructures [Schussel 96].

Three tier with an application server. The three tier application server architecture allocates the main body of an application to run on a shared host rather than in the user system interface client environment. The application server does not drive the GUIs; rather it shares business logic, computations, and a data retrieval engine. Advantages are that with less software on the client there is less security to worry about, applications are more scalable, and support and installation costs are less on a single server than maintaining each on a desktop client [Schussel 96]. The application server design should be used when security, scalability, and cost are major considerations [Schussel 96].

Three tier with an ORB architecture. Currently industry is working on developing standards to improve interoperability and determine what the common Object Request Broker (ORB) will be. Developing client/server systems using technologies that support distributed objects holds great pomise, as these technologies support interoperability across languages and platforms, as well as enhancing maintainability and adaptability of the system. There are currently two prominent distributed object technologies:

* Common Object Request Broker Architecture (CORBA)
* COM/DCOM (see Component Object Model (COM), DCOM, and Related Capabilities).

Industry is working on standards to improve interoperability between CORBA and COM/DCOM. The Object Management Group (OMG) has developed a mapping between CORBA and COM/DCOM that is supported by several products [OMG 96].

Distributed/collaborative enterprise architecture. The distributed/collaborative enterprise architecture emerged in 1993 (see Distributed/Collaborative Enterprise Architectures). This software architecture is based on Object Request Broker (ORB) technology, but goes further than the Common Object Request Broker Architecture (CORBA) by using shared, reusable business models (not just objects) on an enterprise-wide scale. The benefit of this architectural approach is that standardized business object models and distributed object computing are combined to give an organization flexibility to improve effectiveness organizationally, operationally, and technologically. An enterprise is defined here as a system comprised of multiple business systems or subsystems. Distributed/collaborative enterprise architectures are limited by a lack of commercially-available object orientation analysis and design method tools that focus on applications [Shelton 93, Adler 95].

Usage Considerations
Client/server architectures are being used throughout industry and the military. They provide a versatile infrastructure that supports insertion of new technology more readily than earlier software designs.

Maturity
Client/server software architectures have been in use since the late 1980s. See individual technology descriptions for more detail.

Costs and Limitations
There a number of tradeoffs that must be made to select the appropriate client/server architecture. These include business strategic planning, and potential growth on the number of users, cost, and the homogeneity of the current and future computational environment.

Dependencies
If a distributed object approach is employed, then the CORBA and/or COM/DCOM technologies should be considered (see Common Object Request Broker Architecture and Component Object Model (COM), DCOM, and Related Capabilities).

Alternatives
Alternatives to client/server architectures would be mainframe or file sharing architectures.

Complementary Technologies
Complementary technologies for client/server architectures are computer-aided software engineering (CASE) tools because they facilitate client/server architectural development, and open systems (see COTS and Open Systems--An Overview) because they facilitate the development of architectures that improve scalability and flexibility.

Networking : Network Architecture

Network Architecture

The term “network architecture” is commonly used to describe a set of abstract principles for the technical design of protocols and mechanisms for computer communication. A network architecture represents a set of deliberate choices out of many design alternatives, where these choices are informed by an understanding of the requirements. In turn, the architecture provides a guide for the many technical decisions required to standardize network protocols and algorithms. The purpose of the architecture is providing coherence and consistency to these decisions and to ensure that the requirements are met. The design of today’s Internet technology was guided by an Internet architecture that was developed in the 1970s, under the Internet research program of the Defense Advanced Research Projects Agency (DARPA) of the US Department of Defense.

What is Network architecture?

Network architecture is a set of high-level design principles that guides the technical design of the network, especially the engineering of its protocols and algorithms. To flesh out this simple definition, we have examples of the constituents of the architecture and how it is applied.

A network architecture must typically specify:
· Where and how state is maintained and how it is removed.
· What entities are named.
· How naming, addressing, and routing functions inter-relate and how they are performed.
· How communication functions are modularized, e.g., into “layers” to form a “protocol stack”.
· How network resources are divided between flows and how end-systems react to this division, i.e., fairness and congestion control.
· Where security boundaries are drawn and how they are enforced.
· How management boundaries are drawn and selectively pierced.
· How differing QoS is requested and achieved.

Ideally one would like to imagine using the architecture to “generate” the technical design, but making such a mapping in a mechanical fashion is clearly impossible. The architecture can only provide a set of abstract principles against which we can check each decision about the technical design. The role of the architecture is to ensure that the resulting technical design will be consistent and coherent – the pieces will fit together smoothly – and that the design will satisfy the requirements on network function associated with the architecture. An architecture is more general than a particular conformant technical design. The technical design derived from a particular architecture is far from unique, and it may evolve over time in response to detailed changes in requirements; however, the same architecture may be maintained. Crucially, architecture is expected to be relatively long-lived, applicable to more than one generation of the technology.

A trivial example of this is IPv6, which represents a later generation of technology than IPv4 although both conform to the same Internet architecture. An example of architectural thinking was contained in the Application Level Framing (ALF) proposal of Clark and Tennenhouse. ALF was not a complete architecture, only an architectural component with specific goals: lower cost and more flexible implementation, more efficient operation over diverse infrastructure (packet and ATM), and effective support for a wider range of application requirements, and so on. ALF illustrates the practical short-term benefit of long term architectural thinking. While the ALF idea as proposed was not cast as in incremental modification to the internet but rather as a new and different approach, other researchers used the ALF idea as the basis for the implementation of new applications over the existing network.

Antivirus: Working of an antivirus package( part II)

Continued......(from part I)

Now, suppose that a previously unknown strain of the Melissa virus happens to come into contact with your computer. Your antivirus software would use a technology known as heuristics to identify the virus.

Heuristics work on the basis of probability. The basic idea is that a variant of Melissa would still resemble one of the existing versions of Melissa. After all, if it looks like Melissa and it smells like Melissa, then it’s probably Melissa. If the heuristics algorithm causes the virus scanner to uncover a potential variant of a known virus, the scanner will alert you to the fact. When your antivirus software detects an unknown variant and alerts you to the potential virus, what it’s really telling you is that the file has a certain percentage of code in common with a known virus or that the software is a certain percentage certain that the file contains viral code.

Polymorphic viruses
Heuristics are great if the virus remains true to its original form, but virus programmers are smart people. Some viruses are designed to encrypt themselves. Such viruses are known as polymorphic viruses. The idea behind polymorphic viruses is that they can reorganize themselves so as to have an extremely large potential number of signatures.

Fortunately, there’s a way to protect your machine from polymorphic viruses. If the virus scanner suspects a polymorphic virus, some antivirus software packages actually test the code. To do so, they create what’s known as a virtual machine. In a nutshell, a virtual machine is an area of memory that can behave as if it existed in a separate computer.

By opening a potentially hazardous file in a virtual machine, the antivirus software can test the file in a safe and controlled environment. If the file proves to be safe, the user will never know of the test. However, if the file does contain a virus, the user is alerted to the infection and prompted to take action.
The authors and editors have taken care in preparation of the content contained herein but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for any damages. Always have a verified backup before making any changes.