What is a Protocol

A protocol is a set of rules that governs the communications between computers on a network. These rules include guidelines that regulate the following characteristics of a network: access method, allowed physical topologies, types of cabling, and speed of data transfer. See the Topology and Cabling sections of this tutorial for more information.

The most common protocols are:

1. Ethernet.
2. Local Talk.
3. Token Ring.
4. FDDI.
5. ATM.

1.Ethernet

The Ethernet protocol is by far the most widely used. Ethernet uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection). This is a system where each computer listens to the cable before sending anything through the network. If the network is clear, the computer will transmit. If some other node is already transmitting on the cable, the computer will wait and try again when the line is clear. Sometimes, two computers attempt to transmit at the same instant. When this happens a collision occurs. Each computer then backs off and waits a random amount of time before attempting to retransmit. With this access method, it is normal to have collisions. However, the delay caused by collisions and retransmitting is very small and does not normally effect the speed of transmission on the network. The Ethernet protocol allows for linear bus, star, or tree topologies. Data can be transmitted over wireless access points, twisted pair, coaxial, or fiber optic cable at a speed of 10 Mbps up to 1000 Mbps.

What is a Network

A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.
The three basic types of networks include:

• Local Area Network (LAN)
• Wide Area Network (WAN)

Local Area Network
A Local Area Network (LAN) is a network that is confined to a relatively small area. It is generally limited to a geographic area such as a writing lab, school, or building. Rarely are LAN computers more than a mile apart.
In a typical LAN configuration, one computer is designated as the file server. It stores all of the software that controls the network, as well as the software that can be shared by the computers attached to the network. Computers connected to the file server are called workstations. The workstations can be less powerful than the file server, and they may have additional software on their hard drives. On most LANs, cables are used to connect the network interface cards in each computer. See the Topology, Cabling, and Hardware sections of this tutorial for more information on the configuration of a LAN.
Wide Area Network
Wide Area Networks (WANs) connect larger geographic areas, such as Florida, the United States, or the world. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of network.
Using a WAN, schools in Florida can communicate with places like Tokyo in a matter of minutes, without paying enormous phone bills. A WAN is complicated. It uses multiplexers to connect local and metropolitan networks to global communications networks like the Internet. To users, however, a WAN will not appear to be much different than a LAN or a MAN.

Advantages of Installing a School Network:

• Speed. Networks provide a very rapid method for sharing and transferring files. Without a network, files are shared by copying them to floppy disks, then carrying or sending the disks from one computer to another. This method of transferring files (referred to as sneaker-net) is very time-consuming.
• Cost. Networkable versions of many popular software programs are available at considerable savings when compared to buying individually licensed copies. Besides monetary savings, sharing a program on a network allows for easier upgrading of the program. The changes have to be done only once, on the file server, instead of on all the individual workstations.
• Security. Files and programs on a network can be designated as "copy inhibit," so that you do not have to worry about illegal copying of programs. Also, passwords can be established for specific directories to restrict access to authorized users.
• Centralized Software Management. One of the greatest benefits of installing a network at a school is the fact that all of the software can be loaded on one computer (the file server). This eliminates that need to spend time and energy installing updates and tracking files on independent computers throughout the building.
• Resource Sharing. Sharing resources is another area in which a network exceeds stand-alone computers. Most schools cannot afford enough laser printers, fax machines, modems, scanners, and CD-ROM players for each computer. However, if these or similar peripherals are added to a network, they can be shared by many users.
• Electronic Mail. The presence of a network provides the hardware necessary to install an e-mail system. E-mail aids in personal and professional communication for all school personnel, and it facilitates the dissemination of general information to the entire school staff. Electronic mail on a LAN can enable students to communicate with teachers and peers at their own school. If the LAN is connected to the Internet, students can communicate with others throughout the world.
• Flexible Access. School networks allow students to access their files from computers throughout the school. Students can begin an assignment in their classroom, save part of it on a public access area of the network, then go to the media center after school to finish their work. Students can also work cooperatively through the network.
• Workgroup Computing. Workgroup software (such as Microsoft BackOffice) allows many users to work on a document or project concurrently. For example, educators located at various schools within a county could simultaneously contribute their ideas about new curriculum standards to the same document and spreadsheets.

Disadvantages of Installing a School Network:

• Expensive to Install. Although a network will generally save money over time, the initial costs of installation can be prohibitive. Cables, network cards, and software are expensive, and the installation may require the services of a technician.
• Requires Administrative Time. Proper maintenance of a network requires considerable time and expertise. Many schools have installed a network, only to find that they did not budget for the necessary administrative support.
• File Server May Fail. Although a file server is no more susceptible to failure than any other computer, when the files server "goes down," the entire network may come to a halt. When this happens, the entire school may lose access to necessary programs and files.
• Cables May Break. The Topology chapter presents information about the various configurations of cables. Some of the configurations are designed to minimize the inconvenience of a broken cable; with other configurations, one broken cable can stop the entire network.

Upgrading Oracle

Oracle 10i is just around the corner, but recent surveys show that most of you are still using versions 8 or 8i. If you are considering upgrading from your current version, whatever it is, this Ask the Experts compilation can help. In it, Oracle gurus Brian Peasland, Karen Morton and Eli Leiba point out advantages of updating your software, how it will affect applications, hardware requirements and other issues to be aware of during the move.

Can you enumerate the differences between the different versions of Oracle (i.e. disadvantages and advantages)?
Brian Peasland: Oracle databases have been around for quite a while now. Oracle released their 9i (9.0.1) version about a year ago. Many companies are still using the 8i (8.1.x), 8 (8.0.x) and 7.x database versions. For the most part, everything that is available in a lower version will be available in a higher version as well. There are a few minor exceptions, but the Oracle databases tend to be backwards compatible. When Oracle releases a new version, their documentation contains a list of all the features new to that version. So it is worthwhile for the DBA to read this documentation to discover what is new in the database. To give you an idea of what is "new" consider this...Oracle 8i introduced many new features for the developer. With 8i, you could run Java in the database, you had expanded tools to help with object-oriented development and 8i introduced some enhancements to support larger databases (Materialized Views, additions to partitioning). Oracle 9i introduced many new features to help the DBA such as the ability to change database configuration "on the fly", enhanced availability and enhanced managability. The advantage of a higher version is that you have more features and better capabilities. You also stay current with the latest "supported" versions. The disadvantage of these new systems is that you have to convert your older databases to the newer versions. This can sometimes cause application changes as well. The advantage of staying at a lower version is that you know it works and you don't have to change a thing. The disadvantage is that you can't use any of the latest and greatest features and that you may lose support.

What are the main advantages of upgrading from Oracle 7 to Oracle 8i/9i?

1. adding objects to the database
2. adding new data type such as BLOB/CLOB
3. new administrative options like moving tables between tablespaces
4. many NEW dbms packages
5. writing JAVA code inside Oracle
6. passing parameters to sp with the NOCOPY Option
7. smart sqlloader options
8. can work with array types
9. the new log miner.

Security Issues in Wireless LANs-II

Information security has become a buzzword of the twenty-first century. Governments, institutions, enterprises, commercial businesses and individuals are storing
information in electronic form as this has a number of distinct and unique advantages over
physical storage. Storage in electronic form is more compact, transfer is almost instantaneous
and accessing, retrieving, loading, and manipulation of information via databases, is easy.

The need

The ability to use information more efficiently has resulted in a rapid increase in the value of
information. Businesses in a number of commercial arenas today recognise information
as their most valuable asset. So there are a number of mechanisms, products and technologies, which make use of this critical, precise, historical and valuable information in a useful manner to make life-saving decisions. With the electronic revolution, information now faces new and potentially damaging security threats. Unlike information printed on paper, information in electronic form can be stolen from a remote location in an easy and invisible manner.

What is information security?

Information security describes all measures taken to prevent unauthorised use of electronic
data. This unauthorised use may be in the form of disclosure, alteration, substitution or destruction of the data. Information security is classified as the provision of the following three
services:-

Confidentiality: Concealment of data from unauthorised people.

Integrity: Assurance that data is genuine, i.e., the originality has been preserved

Availability: Ensuring that the system functions efficiently after security provisions
are in place.

Why is wireless LAN communication not secure?

In a traditional wired LAN, all communication is confined to a physical link between the workstations. If we protect the workstations and the physical link, we can prevent unauthorised access to the network. But in WLAN, communication is not through a physical link, but is broadcast through the air in all directions simultaneously. It is a bit like tossing a stone into a pond and watching the ripples spread outwards. But while physical obstacles can stop the ripples, wireless broadcasts pass straight through walls, doors, fences, etc. This means that when you send an e-mail to the CEO wirelessly, that e-mail can be received by anybody with the right kind of receiving equipment within the range of ripples. Th e range is generally between 20 and 50 metres without a booster and with a booster it could well be anything up to 500 metres.

Typical wireless security attacks

There are several possible wireless security attacks, such as:

WEP cracking: Wired Equivalent Policy (WEP), the primary security algorithm currently in use, is vulnerable because the encryption keys remain static. The encryption key used by
WEP, regardless of its length, never changes unless it is periodically and manually changed by the administrator on all devices. An attacker uses a relatively inexpensive wireless packet sniffer to collect packets. After gathering five to 10 million packets, the attacker runs readily available tools that can determine encryption keys in a few minutes, enabling him to decrypt
and read all data passing between the client and the access point.

MAC attack: Medium Access Control (MAC) addresses can be cracked in much the same way as WEP encryption keys. Once the encryption key is deciphered, all packet data, including the MAC ID, is exposed. If no encryption is used, the MAC ID can be simply plucked from the air. Once a valid MAC address has been obtained, hackers can program their computer to spoof a valid user by programming a computer to broadcast the stolen ID

Man-in-the-middle attacks: This type of attack characterises a hacker situated between the client and access point, intercepting all traffic. The hacker captures and decrypts the frames sent back and forth between a user’s wireless NIC and AP (access point) during the association process. This provides essential information about the wireless NIC and AP, such as the IP addresses for both devices, the wireless NICs association ID and the network’s SSID (Service Set Identifier). With this information, anyone can set up a rogue access point on a different wireless channel closer to a particular user, to force the user’s wireless NIC to re-associate with the bogus access point. Both the client and the server believe they are connected directly to each other, but instead they are connected to a man in the middle. The attacker has access to all data passed between the two entities, including login information

Dictionary attacks: This kind of attack relies on conventional names and words being used as login names and passwords. The attacker gathers a challenge and response exchange from password-based protocols. Using open source tools based on a dictionary of hundreds of thousands of words, names and phrases, an offline computer tries essentially every name-password combination, until the login information is decrypted. Once a name and password have been cracked, the attacker has access to the WLAN with all the rights and privileges of that user.

Session hijacking: When an attacker is capable of not only listening to network traffic but also inserting his information, then a session is susceptible to hijacking—redirecting it away

WINS

Successfully maintaining a Windows NT Server–based network means using every tool that you have on your shelf. In the world of Windows NT Server 4.0, Windows Internet Naming Service (WINS) is one of those tools. Note that WINS will be displaced by Dynamic DNS in Windows 2000 Server, so in reality, you could say that WINS is on its way out of favor. And although Windows 2000 Server will support WINS for backward compatibility reasons, at this point in the Windows NT Server 4.0 life cycle, you are advised to plan for DNS-based network name resolution and to deemphasize your reliance on WINS. That said, this section will provide you with what you need to know about WINS. It will provide little more given WINS’ impending exit from the Windows NT community. And although you certainly need to know WINS basics, be advised that your time is better spent mastering the first two topics of this chapter (DNS, DHCP).
WINS was designed to eliminate broadcasts and maintain a dynamic database providing computer name–to–IP address mappings.
Note: The key point with WINS is its “dynamic” paradigm. Its database is updated dynamically or on the fly. By contrast, DNS maintains a static database of addresses that may only be upgraded by receiving a propagated delta DNS database periodically.
A WINS system has two components: servers and clients.
WINS servers. WINS servers maintain the database that maps a WINS Client IP address to its NetBIOS computer name. Broadcasts for NetBIOS-type name resolutions are eliminated (or at least reduced) because the database on the WINS server may be consulted for immediate name resolution.
WINS clients. A WINS client is a workstation that is configured with the WINS server(s) IP address(es). At system startup, the WINS client registers its name and IP address with the WINS server. When a WINS client needs a name resolved, the WINS server and its database are consulted. This results in fast and efficient name resolution.
At the enterprise level, a network typically has one or more WINS servers that a WINS client may contact for name resolution. In fact, WINS servers may be configured on a given network so that they replicate all computer names to IP address mappings to each other’s respective databases.
Implementing WINS Server on your Windows NT Server network results in the following benefits:
Reduced broadcast network traffic
No need for an LMHOSTS file
Dynamic name registration
No duplicate computer names
No specific need for a DNS server (although dispensing with one is not recommended!)
How WINS Works Out of the box, when you configure a Windows NT Server–based network to use WINS for its name registration, it adheres to the h-node broadcasting methodology. You will recall the h-node refers to one of the NetBIOS over TCP/IP modes that defines how NBT identifies and accesses resources on a network. During name resolution, the WINS client:
Checks to see if it is the local machine name.
Looks at its cache of remote names. Any name that is resolved is placed in a cache, where it remains for 10-minutes.
Attempts to contact the WINS server.
Attempts broadcasting.
Checks the LMHOSTS file (if it is configured to use and check the LMHOSTS file).
Last, tries the HOSTS file and then DNS (if appropriately configured).
You will recall that this process was previously discussed early in the chapter in the “Be Resolved” section.
Note: If a DHCP client has been configured to use m-node name resolution, the client first attempts to broadcast. The WINS server is consulted second.
When a WINS client boots, a Name Registration Request packet is sent to the WINS server so that the client computer name may be registered. As many Name Registration Request packets are sent as necessary to register names. Not surprisingly, these packets contain the WINS client’s IP address and name. Installing WINS serversYou may elect install a WINS server when you are initially setting up your Windows NT server or at a future date. In order to set up a WINS server, you must be logged on as a member of the Administrator group.
STEPS:
To install a WINS server
Step 1.
Choose the Network applet in Control Panel. The Network dialog box appears.
Step 2.
Select the Services tab sheet in the Network dialog box.
Step 3.
Click the Add button. The Select Network Service dialog box appears.
Step 4.
Select Windows Internet Name Service in the Select Network Service dialog box.
Step 5.
Windows NT Server displays the Windows NT Setup dialog box asking for the complete path to the Windows NT Server distribution. Type in the correct path and click Continue.
Step 6.
Observe that the Windows Internet Name Service appears as one of the Network Services listed on the Service tab sheet of the Network dialog box. Click Close.
Step 7.
Restart the computer. When the computer restarts, the WINS server is ready to receive name registrations and resolve name requests.
Note that the WINS service will be configured to start automatically. It may be stopped via the Services applet in Control Panel. Configuring WINS serversYou will use the WINS Manager located in the Administrator Tools (Common) program group to configure your local and remote WINS servers on your network.The left pane of WINS Manager displays the WINS servers visible on your network. Typically these are shown as IP addresses, but it is entirely possible that the WINS server list will display NetBIOS names (if that is what the specific server supplied). If indeed a computer name is supplied, then WINS Manager establishes a connection to the WINS server via named pipes.
STEPS:
To configure a WINS server
Step 1.
Select the Configuration command from the Server menu.
Step 2.
Click the Advanced button to expand the WINS Server Configuration dialog box.
Step 3.
Configure the WINS Server Configuration dialog box.
Note that advanced WINS configuration topics such as configuring replication partners are considered to be beyond the scope of this book given WINS’ limited life before the release of Windows 2000 Server and its Dynamic DNS solution. If you are interested in advanced WINS configuration topics, I recommend that you consult the Windows NT Server 4.0 Resource Kit or Microsoft TechNet.
Configuring WINS clients
If a client workstation has TCP/IP installed, it may be configured to use a WINS server to perform its computer name–to–IP address resolution. This is accomplished when the client workstation is configured with the IP addresses of the primary and secondary WINS servers.
WINS Server on Windows NT Server 4.0 can support the following WINS clients:
Windows NT Server 4.0
Windows NT Workstation 4.0
Windows 98
Windows 95
Windows for Workgroups 3.11 (WFW) with the Microsoft 32-bit TCP/IP VxD installed.
Note: WFW is one of the clients supported on the Windows NT Server 4.0 CD-ROM in the \i386\clients\msclient directory. This is also one of the clients that is supported and configured via the Network Client Administrator application found in the Administrative Tools (Common) program group. Note this client support also extends to the next two clients (Microsoft Network Client for MS-DOS and LAN Manager for MS-DOS 2.2c).
Microsoft Network Client for MS-DOS with real-mode TCP/IP driver
LAN Manager for MS-DOS 2.2c
If a DHCP server is used to supply TCP/IP configuration information to DHCP clients, such TCP/IP configuration may contain the following WINS configuration information:
044 WINS/NBNS servers configured with an IP address of one or more WINS servers
046 WINS/NBT Node Type set to 0x1 (b-node), 0x2 (p-node), 0x4 (m-node), or 0x8 (h-node). For detailed information on node types, you should consult the Windows NT Server Resource Kit or Microsoft TechNet. Using WINS Manager The great thing about WINS Manager is that after its initial configuration, it becomes a reporting tool for you to observe WINS server–related name resolution activity. This service essentially runs itself. To see detailed information about the current WINS server, select Detailed Information from the Server menu. The Detailed Information dialog box appears. Select the Close button to dismiss the Detailed Information dialog box. Since in all likelihood you and I are both going to be living with Windows NT Server 4.0 for the foreseeable future either as the primary NOS or as a background NOS to Windows 2000 Server, it is prudent to drop down to the WINS engineering level and educated ourselves on the detailed statistics that are reported back from WINS.

Network card

A transitional network card with both BNC "Thin net" (left) and Twisted pair (right) connectors.
A network card (also called network adapter, network interface card, NIC, etc.) is a piece of computer hardware designed to provide for computer communication over a computer network.
Whereas network cards used to be expansion cards to plug into a computer bus, most newer computers have a network interface built into the motherboard, so a separate network card is not required unless multiple interfaces are needed or some other type of network is used.
The card implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as ethernet or token ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP.
A network card typically has a twisted pair, BNC, or AUI socket where the network cable is connected, and a few LEDs to inform the user of whether the network is active, and whether or not there is data being transmitted on it.

DNS

If you spend any time on the Internet sending e-mail or browsing the Web, then you use domain name servers without even realizing it. Domain name servers, or DNS, are an incredibly important but completely hidden part of the Internet, and they are fascinating! The DNS system forms one of the largest and most active distributed databases on the planet. Without DNS, the Internet would shut down very quickly.

The Basics
When you use the Web or send an e-mail message, you use a domain name to do it. For example, the URL "http://www.crispindia.com" contains the domain name crispindia.com. So does the e-mail address "devesh@crispindia.com."
Human-readable names like "crispindia.com" are easy for people to remember, but they don't do machines any good. All of the machines use names called IP addresses to refer to one another. For example, the machine that humans refer to as "www.crispindia.com" has the IP address 64.14.119.232. Every time you use a domain name, you use the Internet's domain name servers (DNS) to translate the human-readable domain name into the machine-readable IP address. During a day of browsing and e-mailing, you might access the domain name servers hundreds of times!
Domain name servers translate domain names to IP addresses. That sounds like a simple task, and it would be -- except for five things:
There are billions of IP addresses currently in use, and most machines have a human-readable name as well.
There are many billions of DNS requests made every day. A single person can easily make a hundred or more DNS requests a day, and there are hundreds of millions of people and machines using the Internet daily.
Domain names and IP addresses change daily.
New domain names get created daily.
Millions of people do the work to change and add domain names and IP addresses every day.
The DNS system is a database, and no other database on the planet gets this many requests. No other database on the planet has millions of people changing it every day, either. That is what makes the DNS system so unique!

IP Addresses
To keep all of the machines on the Internet straight, each machine is assigned a unique address called an IP address. IP stands for Internet protocol, and these addresses are 32-bit numbers normally expressed as four "octets" in a "dotted decimal number." A typical IP address looks like this:
64.14.119.232
The four numbers in an IP address are called octets because they can have values between 0 and 255 (28 possibilities per octet).
Every machine on the Internet has its own IP address. A server has a static IP address that does not change very often. A home machine that is dialing up through a modem often has an IP address that is assigned by the ISP when you dial in. That IP address is unique for your session and may be different the next time you dial in. In this way, an ISP only needs one IP address for each modem it supports, rather than for every customer.
If you are working on a Windows machine, you can view your current IP address with the command WINIPCFG.EXE (IPCONFIG.EXE for Windows 2000/XP). On a UNIX machine, type nslookup along with a machine name to display the IP address of the machine (use the command hostname to learn the name of your machine).
For more information on IP addresses, see IANA.
As far as the Internet's machines are concerned, an IP address is all that you need to talk to a server. For example, you can type in your browser the URL http:// 64.14.119.232 and you will arrive at the machine that contains the Web server for crispindia.com. Domain names are strictly a human convenience.