Antivirus PCMAV 1.7

Bersamaan dengan terbitnya majalah PC Media edisi 10/2008 yang disertai ekstra DVD Buku Sekolah Elektronik (BSE), PC Media Antivirus kembali dirilis versi barunya. Pada rilis kali ini, PCMAV 1.7 mampu mengenali dan mengatasi 2.182 virus beserta variannya yang banyak dilaporkan menyebar di Indonesia.

Pada versi kali ini ditambahkan beberapa rutin cleaner khusus untuk beberapa virus yang dilaporkan banyak menyebar diantaranya seperti Windx-Maxtrox yang dapat menginfeksi masuk ke dalam file executable, atau virus Microso yang dapat melakukan DLL injection. Berikut ini daftar selengkapnya:

APA YANG BARU?

a.Ditambahkan, database pengenal dan pembersih 118 virus
lokal/asing/varian baru yang dilaporkan menyebar di Indonesia.
Total 2182 virus beserta variannya yang banyak beredar di
Indonesia telah dikenal di versi 1.7 ini oleh engine internal PCMAV.

b.Diperbaiki, kesalahan pada rutin yang bertugas melakukan buffering
pada file yang akan di-scan.

c.Ditambahkan, cleaner khusus untuk virus VBScript FourTwoOne.vbs.

d.Ditambahkan, cleaner khusus untuk virus Windx-Maxtrox yang dapat
menginfeksi file executable.

e.Ditambahkan, cleaner khusus untuk virus Microso yang dapat melakukan
injeksi file .DLL.

f.Diperbaiki, kesalahan deteksi (false alarm) heuristik pada beberapa
program ataupun script.

g.Diperbarui, perubahan beberapa nama virus mengikuti varian baru yang
ditemukan.

h.Perbaikan beberapa minor bug dan improvisasi kode internal untuk
memastikan bahwa PCMAV Cleaner & PCMAV RealTime Protector lebih
dari sekadar antivirus biasa.

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Antivirus PCMAV 1.6 + Build 1

Majalah PC Media 09/2008 telah terbit. Bersamaan dengan itu pula antivirus kebanggaan Indonesia, PC Media Antivirus (PCMAV), telah mencapai versi 1.6 dan secara resmi dirilis ke publik. Di rilis kali ini, PCMAV mampu mengatasi 2.064 virus beserta variannya yang banyak dilaporkan menyebar di Indonesia.

Beberapa bug yang ditemukan telah berhasil diperbaiki, seperti bug yang mengakibatkan terganggunya kerja engine heuristic dan perbaikan pada engine GetUpdates. Selain itu, dilakukan beberapa improvisasi seperti contohnya pada engine heuristic “Virus Suspected (RD)”. Berikut ini daftar selengkapnya:

APA YANG BARU?

Ditambahkan, database pengenal dan pembersih 79 virus lokal/asing/varian baru yang dilaporkan menyebar di Indonesia.
Total 2064 virus beserta variannya yang banyak beredar di Indonesia telah dikenal di versi 1.6 ini oleh engine internal PCMAV.

Diperbaiki, bug pada rutin yang bertugas untuk memeriksa kondisi suatu object sebelum scan dilakukan, untuk memastikan bahwa PCMAV telah mendapatkan hak akses baca. Bug ini dapat mengakibatkan terganggunya kerja dari engine heuristic.

Diperbaiki, kesalahan deteksi pada beberapa aplikasi yang dikenalioleh USB Disk Filtering sebagai Virus Suspected.

Diperbaiki, bug pada engine GetUpdates yang terkadang kurang akuratdalam mendeteksi atau melakukan pengecekan terhadap file update baru.

Diperbaiki, kesalahan deteksi (false alarm) pada beberapa program ataupun script.

Improvisasi, engine heuristic untuk Virus Suspected (RD). Kini, engine ini lebih akurat dalam mendeteksi sebuah object.

Improvisasi, user-interface dari USB Disk Filtering.

Diperbarui, perubahan beberapa nama virus mengikuti varian baru yang ditemukan.

Perbaikan beberapa minor bug dan improvisasi kode internal untukmemastikan bahwa PCMAV Cleaner & PCMAV RealTime Protector lebih dari sekadar antivirus biasa.

Silahkan download di sini.

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The Dedicated Server Handbook

Table of Contents :

• Disclaimer
• Introduction
• Why Dedicated?
• Dedicated or Virtual Dedicated?
• Links in this book
• Chapter 1 – Domains
• Getting Your Domain
• Introduction to Domains and DNS
• Chapter 2 – The Webmin Control Panel
• Getting Started With Your New Server
• Installing Webmin
• Binary Install (Recommended)
• Debian Based Binary Install
• RedHat Based Binary Install
• Manual Install (Not For the Faint of Heart)
• Post-Install Configuration of Webmin
• Chapter 3 – DNS
• Introduction to DNS Servers
• Configuring DNS with Bind
• Using a 3
• Party DNS Provider
• Chapter 4 – Users & FTP
• Users
• SFTP
• Normal FTP
• No FTP
• Chapter 5 – The Webserver
• The Apache Webserver
• Preparing The Web Root
• Configuring a VirtualHost inside Apache
• Installing Perl/CGI
• Installing PHP
• Secure (HTTPS) VirtualHosts
• Chapter 6 – Database
• MySQL
• Configuring MySQL using Webmin
• Installing phpMyAdmin
• Configuring MySQL using phpMyAdmin
• Chapter 7 – Email
• How Email Works
• Configuring Sendmail
• AntiVirus Scanning
• Configuring MX Records for Incoming Mail
• Anti-Spam Techniques: SPF
• Chapter 8 – Log-File Analysis
• Webalizer
• Creating a Server-Wide Report
• Creating a Per-Website Report

Download ebook here


Video Setting up the Apache Webserver on a Linux Server - Part 1




View more videos from The Dedicated Server Handbook here

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Javajegeg Toolbar

Anda pengguna IE atau FireFox, dapat memanfaatkan toolbar saya untuk di pasang browser Anda. Sekali pasang Anda dapat memanfaatkan fitur Radio Online, Pembaca Email (Yahoo, Gmail, Hotmail, POP3) secara otomatis, dan Google search.











Download untuk pengguna FireFox



Atau silahkan download dengan klik di sini untuk pengguna IE versi 5+.

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Antivirus PCMAV 1.5 + Build 1

PC Media Antivirus (PCMAV) 1.5 build 1
Copyright (c) 2006-2008 Majalah PC Media
A member of Pinpoint Publications

Antivirus lokal yang paling banyak digunakan pengguna komputer pribadi di Indonesia ini telah mengeluarkan versi terbarunya melalui majalah PC Media 08/2008. Pada rilis kali ini, PCMAV mampu mengenali 1.985 virus (sumber: VirusIndonesia.com )beserta variannya yang banyak dilaporkan menyebar di Indonesia. Beberapa perbaikan & improvisasi kembali dilakukan di versi 1.5 ini, salah satunya adalah kesalahan pada engine yang bertugas melakukan scanning terhadap tipe file autorun yang dapat mengakibatkan RTP crash. Ditambahkan pula engine cleaner khusus yang dapat membersihkan file yang terinfeksi oleh virus Godham agar pulih seperti sedia kala. Dan juga, dilakukan improvisasi pada fitur baru yakni USB Disk Filtering yang sudah menginjak versi Beta2.

Berikut ini daftar selengkapnya:

APA YANG BARU?
a.Ditambahkan, database pengenal dan pembersih 48 virus
lokal/asing/varian baru yang dilaporkan menyebar di Indonesia.
Total 1.985 virus beserta variannya yang banyak beredar di
Indonesia telah dikenal di versi 1.5 ini oleh engine internal PCMAV.

b.Improvisasi, user-interface dari USB Disk Filtering.

c.Diperbaiki, kesalahan pada engine khusus yang melakukan pemeriksaan
terhadap file autorun.inf, yang pada komputer tertentu, khususnya
komputer yang terdapat antivirus lain, akan mengakibatkan RTP crash.

d.Diperbaiki, rutin yang melakukan buffering pada file target yang akan
di-scan. Pada kondisi tertentu, kesalahan ini dapat mengakibatkan crash
pada RTP, khususnya ketika RTP gagal dalam membuka file yang terproteksi.

e.Diperbaiki, kesalahan pada USB Disk Filtering, yang terkadang
mengakibatkan tidak terdeteksinya file autorun.inf milik virus.

f.Diperbaiki, kesalahan pada USB Disk Filtering yang jika melakukan
scan pada file yang sama, pada daftar virus akan terdapat item ganda.

g.Ditambahkan, engine cleaner khusus yang dapat membasmi dan
membersihkan file yang terinfeksi oleh virus Godham agar
kembali seperti semula.

h.Improvisasi, rutin self-check yang dapat memeriksa kondisi PCMAV,
yang dapat memberitahukan jika file PCMAV mengalami perubahan.

i.Diperbaiki, kesalahan deteksi (false alarm) pada beberapa program
ataupun script.

j.Diperbarui, perubahan beberapa nama virus mengikuti varian baru yang
ditemukan.

k.Perbaikan beberapa minor bug dan improvisasi kode internal untuk
memastikan bahwa PCMAV Cleaner & PCMAV RealTime Protector lebih
dari sekadar antivirus biasa.

Silahkan download di sini.
Atau di sini

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OSI Reference Model: Layer 3 Hardware

Russell Hitchcock

The Open System Interconnect (OSI) reference model and its first two layers. In this article I will discuss the third layer; the network layer. The network layer is concerned with getting data from one computer to another. This is different from the data link layer (layer 2) because the data link layer is concerned with moving data from one device to another directly connected device. For example, the data link layer is responsible for getting data from the computer to the hub it is connected to, while the network layer is concerned with getting that same data all the way to another computer, possibly on the other side of the world.

The network layer moves data from one end point to another by implementing the following functions:

• Addressing
• Routing
• Encapsulation
• Fragmentation
• Error handling
• Congestion control

Addressing

Those who have read my previous article may be curious why layer 3 implements addressing when I also said that layer 2 implements addressing. To cure your curiosity, remember that I wrote that the layer 2 address (the MAC address) corresponds to a specific network access point as opposed to an address for an entire device like a computer. Something else to consider is that the layer 3 address is purely a logical address which is independent of any particular hardware; a MAC address is associated with particular hardware and hardware manufacturers.

An example of layer 3 addressing is the Internet Protocol (IP) addressing. An illustration of an IP address can be seen here in figure 1.

Figure 1: Illustration of an IP address (Source:Wikipedia.com)

Routing

It is the job of the network layer to move data from one point to its destination. To accomplish this, the network layer must be able to plan a route for the data to traverse. A combination of hardware and software routines accomplish this task known as routing. When a router receives a packet from a source it first needs to determine the destination address. It does this by removing the headers previously added by the data link layer and reading the address from the predetermined location within the packet as defined by the standard in use (for example, the IP standard).

Once the destination address is determined the router will check to see if the address is within its own network. If the address is within its own network the router will then send the packet down to the data link layer (conceptually speaking that is) which will add headers as I described in my previous article (link previous article to my OSI Layer 2 article) and will send the packet to its destination. If the address is not within the router's own network, the router will look up the address in a routing table. If the address is found within this routing table the router will read the corresponding destination network from the table and send the packet down to the data link layer and on to that destination network. If the address is not found in this routing table the packet will be sent for error handling. This is one source of errors which can be seen in data transmission across networks, and is an excellent example of why error checking and handling is required.

Encapsulation

When a router sends a packet down to the data link layer which then adds headers before transmitting the packet to its next point, this is an example of encapsulation for the data link layer.
Like the data link layer, the network layer is also responsible for encapsulating data it receives from the layer above it. In this case it would be from the data received from layer 4, the transport layer. Actually, every layer is responsible for encapsulating data it receives from the layer above it. Even the seventh and last layer, the application layer, because an application encapsulates data it receives from users.

Fragmentation

When the network layer sends data down to the data link layer it can sometimes run into trouble. That is, depending on what type of data link layer technology is in use the data may be too large. This requires the network layer have the ability to split the data up into smaller chunks which can each be sent to the data link layer in turn. This process is known as fragmentation.

Error handling

Error handling is an important aspect of the network layer. As I mentioned earlier, one source of errors is when routers do not find the destination address in their routing table. In that case, the router needs to generate a destination unreachable error. Another possible source of errors is the TTL (time to live) value of the packet. If the network layer determines that the TTL has reached a zero value, a time exceeded error is generated. Both the destination unreachable error and the time exceeded error messages conform to specific standards as defined in the Internet Control Message Protocol (ICMP).

Fragmentation can also cause errors. If the fragmentation process takes too long, the device can throw an ICMP time exceeded error.

Congestion control

Another responsibility of the network layer is congestion control. As I am sure you know, any given network device has an upper limit as to the amount of throughput the device can handle. This upper limit is always creeping upward but there are still times when there is just too much data for the device to handle. This is the motivation for congestion control.

There are many theories for how to best accomplish this, most of which are quite complicated and beyond the scope of this article. The basic idea of all of these methods is that you want to make the data senders compete for their messages to be the ones to get accepted into the throughput. The congested device wants to do this in a way that lowers the overall amount of data it is receiving. This can be accomplished by 'punishing' the senders which are sending the most data which causes the senders to 'slow' their sending activity to avoid the punishment and thereby reducing the amount of data seen by the congested device (which at this point is no longer congested).

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Yahoo Mail hopes to lure users with 'ymail.com'

Stephen Shankland

Yahoo Mail, the top provider of Web-based e-mail, is letting users sign up with the ymail.com and rocketmail.com domains in an attempt to attract new users and keep existing ones loyal.

Yahoo headquarters in Sunnyvale, Calif.

The move is geared to help people find a better e-mail address, said John Kremer, vice president of Yahoo Mail. "We want users to get the exact e-mail account they want so they stay with us for life," he said.

Because "yourname@yahoo.com" is likely taken by now, a lot of people must resort to unpleasant and hard-to-remember addresses such as "yourname1988@yahoo.com." Yahoo wants to give people a new chance with a name they like.

The rocketmail name dates back to Yahoo's $92 million acquisition in 1997 of Four11, a company that offered the free RocketMail service.

"It's a great brand," Kremer said. "Those who have no memory of our service in the late 1990s indicated they like it, and those who indicated they want to be retro like it for the fact that it's associated with Yahoo.com since the beginning."

Maybe it's retro for Yahoo, too, which is under fire from shareholders after a bruising takeover attempt by Microsoft. Probably plenty of employees enjoy thinking nostalgically about the company's dot-com glory days. But the company is trying to move forward, too, with Mail one major part of the company's Yahoo Open Strategy (YOS) strategy.

Open mail
Through YOS, Yahoo is trying to make its online services a foundation for third-party applications. For mail, that means letting other applications appear on the Mail "canvas," Kremer said.

In this area, Kremer said, Yahoo was inspired by technology the Yahoo got through its acquisition of online e-mail specialist Zimbra in 2007.

"Zimbra was a pioneer in opening up Web services within the Zimbra application. They have open applications within their space that are used all over the place," he said.

There are now "no walls" between Yahoo Mail and Zimbra engineers, he added, though the business units are separate. "They share a lot of what they do. You'll see in very short order products on our site built on their technology, and vice versa," Kremer said.

The Internet company revamped its Yahoo Mail interface beginning three years ago, calling the update the "all-new Yahoo Mail" for well over a year now. The new interface is based on technology from Yahoo's 2004 acquisition of Oddpost.com.

The "all-new" badge will be removed "pretty soon," Kremer added.

Rolling Thunder
Yahoo plans a "rolling thunder of announcements" around Yahoo Mail in the next six to eight months, he added. Some significant changes will include as a "smarter inbox," work to make Yahoo Mail fit better in today's world of social networking, and the opening of the mail platform, he added.

It's a good thing, because there are plenty of competitors--not just traditional Web mail outfits such as Microsoft Hotmail, AOL, and up-and-coming Google Gmail, but also social sites such as Facebook and MySpace. Yahoo considers the full spectrum of competition, though.

"What we believe here at Yahoo is all communication is eventually coming together," Kremer said. "You don't need to bounce out to a separate social communications site or a different social event site when most of those tools are really just communications. If it's built on the same address book and calendar information, you can see them coming together in a single, more productive, smarter inbox."

Get it now or get this

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How to configure DNS for Internet access in Windows Server 2003

How to Start with a Stand-Alone Server Running Windows Server 2003

The stand-alone server running Windows Server 2003 becomes a DNS server for your network. In the first step, you assign this server a static Internet Protocol (IP) address. DNS servers must not use dynamically assigned IP addresses because a dynamic change of address could cause clients to lose contact with the DNS server.

Step 1: Configure TCP/IP

1.	Click Start, point to Control Panel, point to Network Connections, and then click Local Area Connection.
2.	Click Properties.
3.	Click Internet Protocol (TCP/IP), and then click Properties.
4.	Click the General tab.
5.	Click Use the following IP address, and then type the IP address, subnet mask, and default gateway address in the appropriate boxes.
6.	Click Advanced, and then click the DNS tab.
7.	Click Append primary and connection specific DNS suffixes.
8.	Click to select the Append parent suffixes of the primary DNS suffix check box.
9.	Click to select the Register this connection's addresses in DNS check box. Note that DNS servers running Windows Server 2003 must point to themselves for DNS. If this server needs to resolve names from its Internet service provider (ISP), you must configure a forwarder. Forwarders are discussed in the How to Configure Forwarders section later in this article.
10.	Click OK three times. NOTE: If you receive a warning from the DNS Caching Resolver service, click OK to dismiss the warning. The caching resolver is trying to contact the DNS server, but you have not finished configuring the server.

Step 2: Install Microsoft DNS Server

1.	Click Start, point to Control Panel, and then click Add or Remove Programs.
2.	Click Add or Remove Windows Components.
3.	In the Components list, click Networking Services (but do not select or clear the check box), and then click Details.
4.	Click to select the Domain Name System (DNS) check box, and then click OK.
5.	Click Next.
6.	When you are prompted, insert the Windows Server 2003 CD-ROM into the computer's CD-ROM or DVD-ROM drive.
7.	On the Completing the Windows Components Wizard page, click Finish when Setup is complete.
8.	Click Close to close the Add or Remove Programs window.

Step 3: Configure the DNS Server

To configure DNS by using the DNS snap-in in Microsoft Management Console (MMC), follow these steps:

1.	Click Start, point to Programs, point to Administrative Tools, and then click DNS.
2.	Right-click Forward lookup zones, and then click New Zone
3.	When the New Zone Wizard starts, click Next. You are prompted for a zone type. The zone types include: • Primary zone: Creates a copy of a zone that can be updated directly on this server. This zone information is stored in a .dns text file. • Secondary zone: A standard secondary zone copies all of the information from its master DNS server. A master DNS server can be an Active Directory, primary, or secondary zone that is configured for zone transfers. Note that you cannot modify the zone data on a secondary DNS server. All of its data is copied from its master DNS server. • Stub zone: A Stub zone contains only those resource records that are necessary to identify the authoritative DNS servers for that zone. Those resource records include Name Server (NS), Start of Authority (SOA), and possibly glue Host (A) records. There is also an option to the store zone in Active Directory. This option is only available if the DNS server is a Domain controller.
4.	The new forward lookup zone must be a primary or an Active Directory-integrated zone so that it can accept dynamic updates. Click Primary, and then click Next.
5.	The new zone contains the locator records for this Active Directory-based domain. The name of the zone must be the same as the name of the Active Directory-based domain, or be a logical DNS container for that name. For example, if the Active Directory-based domain is named "support.microsoft.com", valid zone names are "support.microsoft.com" only. Accept the default name for the new zone file. Click Next. NOTE: Experienced DNS administrators may want to create a reverse lookup zone, and are encouraged to explore this branch of the wizard. A DNS server can resolve two basic requests: a forward lookup and a reverse lookup. A forward lookup is more common. A forward lookup resolves a host name to an IP address with an "A" or Host Resource record. A reverse lookup resolves an IP address to a host name with a PTR or Pointer Resource record. If you have your reverse DNS zones configured, you can automatically create associated reverse records when you create your original forward record.

How to Remove the Root DNS Zone

A DNS server running Windows Server 2003 follows specific steps in its name-resolution process. A DNS server first queries its cache, it checks its zone records, it sends requests to forwarders, and then it tries resolution by using root servers.

By default, a Microsoft DNS server connects to the Internet to process DNS requests more with root hints. When you use the Dcpromo tool to promote a server to a domain controller, the domain controller requires DNS. If you install DNS during the promotion process, a root zone is created. This root zone indicates to your DNS server that it is a root Internet server. Therefore, your DNS server does not use forwarders or root hints in the name-resolution process.

1.	Click Start, point to Administrative Tools, and then click DNS.
2.	Expand ServerName, where ServerName is the name of the server, click Properties and then expand Forward Lookup Zones.
3.	Right-click the "." zone, and then click Delete.

How to Configure Forwarders

Windows Server 2003 can take advantage of DNS forwarders. This feature forwards DNS requests to external servers. If a DNS server cannot find a resource record in its zones, it can send the request to another DNS server for additional attempts at resolution. A common scenario might be to configure forwarders to your ISP's DNS servers.

1.	Click Start, point to Administrative Tools, and then click DNS.
2.	Right-click ServerName, where ServerName is the name of the server, and then click the Forwarders tab.
3.	Click a DNS domain in the DNS domain list. Or, click New, type the name of the DNS domain for which you want to forward queries in the DNS domain box, and then click OK.
4.	In the Selected domain's forwarder IP address box, type the IP address of the first DNS server to which you want to forward, and then click Add.
5.	Repeat step 4 to add the DNS servers to which you want to forward.
6.	Click OK.

How to Configure Root Hints

Windows can use root hints. The Root Hints resource records can be stored in either Active Directory or in a text file (%SystemRoot%\System32\DNS\Cache.dns). Windows uses the standard Internic root server. Also, when a server running Windows Server 2003 queries a root server, it updates itself with the most recent list of root servers.

1.	Click Start, point to Administrative Tools, and then click DNS.
2.	Right-click ServerName, where ServerName is the name of the server, and then click Properties.
3.	Click the Root Hints tab. The DNS server's root servers are listed in the Name servers list. If the Root Hints tab is unavailable, your server is still configured as a root server. See the How to Remove the Root DNS Zone section earlier in this article. You may have to use custom root hints that are different from the default. However, a configuration that points to the same server for root hints is always incorrect. Do not modify your root hints. If your root hints are incorrect and have to be replaced, click the following article number to view the article in the Microsoft Knowledge Base: 237675 (http://support.microsoft.com/kb/237675/) Setting up the Domain Name System for Active Directory

How to Configure DNS Behind a Firewall

Proxy and Network Address Translation (NAT) devices can restrict access to ports. DNS uses UDP port 53 and TCP port 53. The DNS Service Management console also uses RCP. RCP uses port 135. These are potential issues that may occur when you configure DNS and firewalls.

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Teknik Professional Photoshop CS3

Buku ini memang bukan saya yang membuat, kebetulan saya browsing dan mendapat link tentang buku ini yang di upload seseorang di suatu forum tetangga.

Karena isinya sepertinya cukup bagus maka sayapun tertarik mengunduhnya. Mungkin sangat berguna bagi yang mau atau pernah belajar Photoshop, diantaranya tentu adalah Anda sendiri.

Silahkan download di sini.

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Antivirus PCMAV 1.4 + USB Disk Filtering

PC Media Antivirus (PCMAV) 1.4
Copyright (c) 2006-2008 Majalah PC Media
A member of Pinpoint Publications

Antivirus lokal yang paling banyak digunakan pengguna komputer pribadi di Indonesia ini telah mengeluarkan versi terbarunya melalui majalah PC Media 07/2008. Fitur baru yang diunggulkan dalam PCMAV 1.4 ini adalah adanya USB Disk Filtering sebagai pengembangan fitur AutoScan yang selama ini ada di RTP, yang memungkinkan ketika sebuah USB Flash Disk dicolokkan, secara otomatis USB Disk Filtering akan bekerja dengan melakukan pemeriksaan.

Di rilis kali ini, PCMAV mampu mengenali 1.937 virus beserta variannya yang banyak dilaporkan menyebar di Indonesia, seperti yang dilaporkan oleh VirusIndonesia.com.

Silahkan download di sini.

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Networking Basics: Part 1 - Networking Hardware

Network Adapters

The first piece of hardware that I want to discuss is a network adapter. There are many different names for network adapters, including network cards, Network Interface Cards, NICs. These are all generic terms for the same piece of hardware. A network card’s job is to physically attach a computer to a network, so that the computer can participate in network communications.

Figure A: This is what an Ethernet card looks like

The first thing that you need to know about network cards is that the network card has to match the network medium. The network medium refers to the type of cabling that is being used on the network. Wireless networks are a science all their own, and I will talk about them in a separate article.

At one time making sure that a network card matched the network medium was a really big deal, because there were a large number of competing standards in existence. For example, before you built a network and started buying network cards and cabling, you had to decide if you were going to use Ethernet, coaxal Ethernet, Token Ring, Arcnet, or one of the other networking standards of the time. Each networking technology had its strengths and weaknesses, and it was important to figure out which one was the most appropriate for your organization.

Today, most of the networking technologies that I mentioned above are quickly becoming extinct. Pretty much the only type of wired network used by small and medium sized businesses is Ethernet. You can see an example of an Ethernet network card, shown in Figure A.

Modern Ethernet networks use twisted pair cabling containing eight wires. These wires are arranged in a special order, and an RJ-45 connecter is crimped onto the end of the cable. An RJ-45 cable looks like the connector on the end of a phone cord, but it’s bigger. Phone cords use RJ-11 connectors as opposed to the RJ-45 connectors used by Ethernet cable. You can see an example of an Ethernet cable with an RJ-45 connector, shown in Figure B.

Figure B: This is an Ethernet cable with an RJ-45 connector installed

Hubs and Switches

As you can see, computers use network cards to send and receive data. The data is transmitted over Ethernet cables. However, you normally can’t just run an Ethernet cable between two PCs and call it a network.

In this day and age of high speed Internet access being almost universally available, you tend to hear the term broadband thrown around a lot. Broadband is a type of network in which data is sent and received across the same wire. In contrast, Ethernet uses Baseband communications. Baseband uses separate wires for sending and receiving data. What this means is that if one PC is sending data across a particular wire within the Ethernet cable, then the PC that is receiving the data needs to have the wire redirected to its receiving port.

You can actually network two PCs together in this way. You can create what is known as a cross over cable. A cross over cable is simply a network cable that has the sending and receiving wires reversed at one end, so that two PCs can be linked directly together.

The problem with using a cross over cable to build a network is that the network will be limited to using no more and no less than two PCs. Rather than using a cross over cable, most networks use normal Ethernet cables that do not have the sending and receiving wires reversed at one end.

Of course the sending and receiving wires have to be reversed at some point in order for communications to succeed. This is the job of a hub or a switch. Hubs are starting to become extinct, but I want to talk about them any way because it will make it easier to explain switches later on.

There are different types of hubs, but generally speaking a hub is nothing more than a box with a bunch of RJ-45 ports. Each computer on a network would be connected to a hub via an Ethernet cable. You can see a picture of a hub, shown in Figure C.

Figure C: A hub is a device that acts as a central connection point for computers on a network

A hub has two different jobs. Its first job is to provide a central point of connection for all of the computers on the network. Every computer plugs into the hub (multiple hubs can be daisy chained together if necessary in order to accommodate more computers).

The hub’s other job is to arrange the ports in such a way so that if a PC transmits data, the data is sent over the other computer’s receive wires.

Right now you might be wondering how data gets to the correct destination if more than two PCs are connected to a hub. The secret lies in the network card. Each Ethernet card is programmed at the factory with a unique Media Access Control (MAC) address. When a computer on an Ethernet network transmits data across an Ethernet network containing PCs connected to a hub, the data is actually sent to every computer on the network. As each computer receives the data, it compares the destination address to its own MAC address. If the addresses match then the computer knows that it is the intended recipient, otherwise it ignores the data.

As you can see, when computers are connected via a hub, every packet gets sent to every computer on the network. The problem is that any computer can send a transmission at any given time. Have you ever been on a conference call and accidentally started to talk at the same time as someone else? This is the same thing that happens on this type of network.

When a PC needs to transmit data, it checks to make sure that no other computers are sending data at the moment. If the line is clear, it transmits the necessary data. If another computer tries to communicate at the same time though, then the packets of data that are traveling across the wire collide and are destroyed (this is why this type of network is sometimes referred to as a collision domain). Both PCs then have to wait for a random amount of time and attempt to retransmit the packet that was destroyed.

As the number of PCs on a collision domain increases, so does the number of collisions. As the number of collisions increase, network efficiency is decreased. This is why switches have almost completely replaced hubs.

A switch, such as the one shown in Figure D, performs all of the same basic tasks as a hub. The difference is that when a PC on the network needs to communicate with another PC, the switch uses a set of internal logic circuits to establish a dedicated, logical path between the two PCs. What this means is that the two PCs are free to communicate with each other, without having to worry about collisions.

Figure D: A switch looks a lot like a hub, but performs very differently

Switches greatly improve a network’s efficiency. Yes, they eliminate collisions, but there is more to it than that. Because of the way that switches work, they can establish parallel communications paths. For example, just because computer A is communicating with computer B, there is no reason why computer C can’t simultaneously communicate with computer D. In a collision domain, these types of parallel communications would be impossible because they would result in collisions.

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