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Computer Networking

Published on March 2017 | Categories: Documents | Downloads: 6 | Comments: 0



Computer Networking Basics & Troubleshooting

Computer Network

What is meant by the term “Computer Network?”

 

Computers linked together. To connect two or more computers together with the ability to communicate with each other.

“Computer Network” is an interconnected collection of autonomous computers.

2 or more computers are said to be interconnected if they are able to exchange information.

Note:-By requiring the computers to be autonomous means ‘there is no master/slave’ relationship. If one computer can forcibly start, stop or control other, the computers are not autonomous.

A computer network is a system for communication between computers. These networks may be fixed (cabled, permanent) or temporary (as via modems).

In the simplest sense, networking means connecting computers so that they can share files, printers, applications, and other computerrelated resources.

We connect the computers to share: • • • • • Folders Peripheral Devices Messages Applications Database

Other devices give capability for sharing above, but they do not get shared.

Goals of computer networking:

   

Increased manageability Security Efficiency Cost-effectiveness

Categorizing Computer Networks

   Local Area Networks Metropolitan Area Networks Wide Area Networks

 

Client - Server Peer To Peer (P2P)

Local Area Network

A local area network (LAN) is a computer network covering a small local area, like a home, office or small group of buildings such as a college. Current LANs are most likely to be based on switched Ethernet or Wi-Fi technology running at from 10 to 1000Mb/s (megabits per second).

Metropolitan Area Network

Metropolitan Area Networks (MAN) are large computer networks usually spanning a campus or a city. They typically use wireless infrastructure or optical fiber connections to link their sites.

Wide Area Network

A wide area network (WAN) is a computer network covering a wide geographical area, involving a vast array of computers. This is different from personal area networks (PANs), metropolitan area networks (MANs) or local area networks (LANs) that are usually limited to a room, building or campus. The best example of a WAN is the Internet.

WANs are used to connect local area networks (LANs) together, so that users and computers in one location can communicate with users and computers in other locations.

Client - Server

The Client/Server is a scalable architecture, whereby each computer or process on the network is either a client or a server. The no. of client computers is more than the Server Computers in such networks.

Server software generally runs on powerful computers dedicated for running an application.

Client software generally runs on common PCs or workstations. Clients get most of their information and rely on the application server for things such as files, business application programs, or to offload compute-intensive application tasks back to the server in order to keep the client computer free to perform other tasks. Properties of a server: • • • Passive (Slave) Waiting for requests On requests serves them and send a reply

Properties of a client: • Active (Master)

• •

Sending requests Waits until reply arrives

Client - Server

A typical example for a Client – Server architecture is an FTP server where the client and server programs are quite distinct, clients initiate the download/uploads and the servers respond to requests.

Another example for a Client – Server architecture is Domain trees & forests of active directory.

Peer to Peer ( P2P)

Peer-to-Peer, or abbreviated P2P, is a type of network in which each workstation has equivalent capabilities and responsibilities.

This differs from client/server architectures, in which some computers are dedicated to serving the others. Peer-to-peer networks are generally simpler, but they usually do not offer the same performance under heavy loads.

A pure peer-to-peer network does not have the notion of clients or servers, but only equal peer nodes that simultaneously function as both "Clients" and "servers" to the other nodes on the network. This model Of network arrangement differs from the client-server model where Communication is usually to and from a central server.

It relies on the computing power and bandwidth of the participants in

the network rather than concentrating it in a relatively few servers.

P2P networks are typically used for connecting nodes via largely ad hoc connections. Such networks are useful for many purposes, like haring content files containing audio, video, data or anything in digital format.

An example of Peer-to-peer networking is the implementation of a

Workgroup consisting of computers running Microsoft Windows or

any other network operating system.

Comparison  P-2-P (Workgroup) • • • • • • Easy Administration No Sys. Admin required Low cost Group of small n/w No or Low Security Segregated Resources & Management

Client-Server • • • • • • Difficult administration Needs Sys Admin High Cost (h/w) Very large n/w High Security Centralized Resource & management

Domain & Workgroup

Workgroup: A logical grouping of networked computers that can share resources with each other. Also called peer-to-peer n/w. A user who wants to log on to a computer must have an account in that computer’s local security database. A user with an account on one computer doesn’t necessarily have any permissions or rights to resources on other computers.

Domain: a collection of computers that share a common domain database and security policy. The domain database is stored by one or more Servers called “domain controller”. Workstations are members of domain. Administrator can control users, computers & other resources centrally from DC.

As the data is stored centrally, a user can use his account name & password to log on to any member computer (provided he has rights to do so).

Network Topology

A network topology is the pattern of links connecting pairs of nodes of a network. A given node has one or more links to others, and the links can appear in a variety of different shapes.

 

Bus network topology Star network topology

    Ring network topology Mesh network topology Tree network topology Fully Connected

Difference b/w LAN & WAN

The defining characteristics of LANs in contrast to WANs are:

• • •

much higher data rates, smaller geographic range, and they do not involve leased telecommunication lines.

OSI Reference Model

Virtually all networks in use today are based in some fashion on the Open Systems Interconnection (OSI) standard. OSI was developed in 1984 by the International Organization for Standardization (ISO), a global federation of national standards organizations representing approximately 130 countries. The core of this standard is the OSI Reference Model, a set of seven layers that define the different stages that data must go through to travel from one device to another over a network.


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Layer 7: Application - This is the layer that actually interacts with the operating system or application whenever the user chooses to transfer files, read messages or perform other network-related activities. Layer 6: Presentation - Layer 6 takes the data provided by the Application layer and converts it into a standard format that the other layers can understand. Layer 5: Session - Layer 5 establishes, maintains and ends communication with the receiving device.

Layer 4: Transport - This layer maintains flow control of data and provides for error checking and recovery of data between the devices. Flow control means that the Transport layer looks to see if data is coming from more than one application and integrates each application's data into a single stream for the physical network. Layer 3: Network - The way that the data will be sent to the recipient device is determined in this layer. Logical protocols, routing and addressing are handled here.

Layer 2: Data - In this layer, the appropriate physical protocol is assigned to the data. Also, the type of network and the packet sequencing is defined.

Layer 1: Physical - This is the level of the actual hardware. It defines the physical characteristics of the network such as connections, voltage levels and timing.

The OSI Reference Model is really just a guideline. Actual protocol stacks often combine one or more of the OSI layers into a single layer. TCP/IP Model

The TCP/IP architectural model has four layers that approximately match six of the seven layers in the OSI Reference Model. The TCP/IP model does not address the physical layer, which is where hardware devices reside. The next three layers—network interface, internet and (host-to-host) transport —correspond to layers 2, 3 and 4 of the OSI model. The TCP/IP application layer conceptually “blurs” the top three OSI layers.



A set of rules for sending information over a network. Protocols can include rules concerning any or all of the following functions:

     

Data transmission mechanisms Communication session initialization and termination Addressing and routing Authentication and verification Encryption and compression Error correction

Note:-Protocols are usually classified according to the layer they correspond to in the Open Systems Interconnection (OSI) reference model for networking.

Protocol Stacks

A protocol stack is a group of protocols that all work together to allow software or hardware to perform a function. The TCP/IP protocol stack is a good example. It uses four layers that map to the OSI model as follows:

Layer 1: Network Interface - This layer combines the Physical and Data layers and routes the data between devices on the same network. It also manages the exchange of data between the network and other devices.

Layer 2: Internet - This layer corresponds to the Network layer. The Internet Protocol (IP) uses the IP address, consisting of a Network Identifier and a Host Identifier, to determine the address of the device it is communicating with.

Layer 3: Transport - Corresponding to the OSI Transport layer, this is the part of the protocol stack where the Transport Control Protocol (TCP) can be found. TCP works by asking another device on the network if it is willing to accept information from the local device. Protocols : UDP, TCP.

Layer 4: Application - Layer 4 combines the Session, Presentation and Application layers of the OSI model. Protocols for specific functions such as e-mail (Simple Mail Transfer Protocol, SMTP) and file transfer (File Transfer Protocol, FTP) & HTTP reside at this level.


        HTTP FTP SMTP TCP UDP IP ARP ICMP Internet Control Message Protocol

Network Address

An identifier for a computer or device on a TCP/IP network.

Note:-There are two types of addresses each computer need to have if it needs to be on the network:

(a) (b)

Physical Address (MAC address). Logical Address (IP Address).

MAC Address

Media Access Control (MAC) Address is a unique 6-byte (48-bit) address that is usually permanently burned into a network interface card (NIC) or other physical-layer networking device and that uniquely identifies the device on an Ethernet-based network. A MAC address is also known as an Ethernet address, hardware address, physical address, or PHY address.

Note:-Every device and port that connects to an Ethernet LAN requires a MAC address.

The uniqueness of MAC addresses is ensured by the Institute of Electrical and Electronics Engineers (IEEE), which assigns networking device vendors specific blocks of MAC addresses for the devices they produce. The first 3 bytes (24 bits) represent the manufacturer of the card, and the last 3 bytes (24 bits) identify the particular card from that manufacturer. Each group of 3 bytes can be represented by 6 hexadecimal digits, forming a 12digit hexadecimal number representing the entire MAC address. Examples of manufacturer 6-digit numbers include the following:

      

00000C (Cisco) 00001D (Cabletron) 0004AC (IBM [PCMCIA Ethernet adapter]) 0020AF (3Com) 00C0A8 (GVC) 080007 (Apple) 080009 (Hewlett-Packard)

Some NICs come with a software utility that you can use to change the MAC address of the card. Changing the address is not a good idea! If you accidentally configure two network cards on your network to have the same MAC address, address conflict problems will result and the computers will not be able to communicate on the network.

To know MAC address of your computer’s NIC:  From the Windows 95 or Windows 98 Run dialog box: winipcfg

 From the Windows NT/2000/XP/2003: command prompt: ipconfig /all

IP Address

A 32-bit (for IPv4) logical address for a host on a TCP/IP network. Each host on a TCP/IP network needs a unique IP address for communication to take place reliably on the network.

The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255 (with some restrictions). For example, could be an IP address.

A Typical IP address looks like this:

To make it easy to remember, IP addresses are normally expressed in decimal format as a "dotted decimal number" like the one above. But computers communicate in binary form. Look at the same IP address in binary: 11011000.00011011.00111101.10001001

The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers. Since each of the eight positions can have two different states (1 or 0) the total number of possible combinations per octet is 28 or 256. So each octet can contain any value between 0 and 255. Combine the four octets and you get 232 or a possible 4,294,967,296 unique values!

Address Resolution Protocol (ARP)

A TCP/IP network layer protocol responsible for resolving IP addresses into MAC addresses.

When a TCP/IP-aware application tries to access another TCP/IP host using its IP address, the destination host’s IP address must first be resolved into a MAC address so that the frame can be addressed and placed on the wire and then be recognized by the destination host’s network interface card (NIC). This is because network interface cards operate at the physical layer (layer 1) and data-link layer (layer 2) of the Open Systems Interconnection (OSI) reference model and must use physical addresses (such as MAC addresses) instead of logical addresses (such as IP addresses) for network communication.

Address Resolution Protocol (ARP)


IP Address

The IP address of a host is partitioned by the network’s subnet mask into two parts, a network ID and a host ID.


Subnet Mask

Subnet masks are used by TCP/IP services and applications to determine whether a given IP address on an internet work is a local network address or a remote network address. It’s a 32-bit number that is used to partition IP addresses into a network ID and a host ID.

How Subnet mask Works

A subnet mask consists of 32 binary digits, the first n of which are 1s and the remaining of which are 0s. When the subnet mask is logically ANDed with a 32-bit IP address of a TCP/IP host, the result is the network ID of the host—the portions of the host’s IP address that identifies which network the host is on. When the inverse of the subnet mask (for example, NOT mask) is logically ANDed with the IP address of the host, the result is the host ID of the host—the portion of the host’s IP address that uniquely identifies the host on its network.


IP Address Classes

The octets serve a purpose other than simply separating the numbers. They are used to create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need. The octets are split into two sections: Net and Host. The Net section always contains the first octet. It is used to identify the network that a computer belongs to. Host (sometimes referred to as Node) identifies the actual computer on the network. The Host section always contains the last octet. There are five IP classes plus certain special addresses:

Default Network - The IP address of is used for the default network.

Class A - This class is for very large networks, such as a major international company might have. IP addresses with a first octet from 1 to 126 are part of this class. The other three octets are used to identify each host. This means that there are 126 Class A networks each with 16,777,214 (224 -2) possible hosts for a total of 2,147,483,648 (231) unique IP addresses. Class A networks account for half of the total available IP addresses. In Class A networks, the high order bit value (the very first binary number) in the first octet is always 0.

Net 115. 

Host or Node 24.53.107

Loopback - The IP address is used as the loopback address. This means that it is used by the host computer to send a message back to itself. It is commonly used for troubleshooting and network testing.

Class B - Class B is used for medium-sized networks. A good example is a large college campus. IP addresses with a first octet from 128 to 191 are part of this class. Class B addresses also include the second octet as part of the Net identifier. The other two octets are used to identify each host. This means that there are 16,384 (214) Class B networks each with 65,534 (216 -2) possible hosts for a total of 1,073,741,824 (230) unique IP addresses. Class B networks make up a quarter of the total available IP addresses. Class B networks have a first bit value of 1 and a second bit value of 0 in the first octet.

Net 145.24. 53.107

Host or Node


Class C - Class C addresses are commonly used for small to mid-size businesses. IP addresses with a first octet from 192 to 223 are part of this class. Class C addresses also include the second and third octets as part of the Net identifier. The last octet is used to identify each host. This means that there are 2,097,152 (221) Class C networks each with 254 (28 -2) possible hosts for a total of 536,870,912 (229) unique IP addresses. Class C networks make up an eighth of the total available IP addresses. Class C networks have a first bit value of 1, second bit value of 1 and a third bit value of 0 in the first octet.

Net 195.24.53. 107

Host or Node

Class D - Used for multicasts, Class D is slightly different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 0. The other 28 bits are used to identify the group of computers the multicast message is intended for. Class D accounts for 1/16th (268,435,456 or 228) of the available IP addresses.

Net 224.

Host or Node 24.53.107

Class E - Class E is used for experimental purposes only. Like Class D, it is different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 1. The other 28 bits are used to identify the group of computers the multicast message is intended for. Class E accounts for 1/16th (268,435,456 or 228) of the available IP addresses.

Net 240.

Host or Node 24.53.107

Broadcast - Messages that are intended for all computers on a network are sent as broadcasts. These messages always use the IP address

Networks that are directly connected to the Internet must have their IP addresses assigned by the Internet Network Information Center (InterNIC) or some other authority. Businesses usually obtain these addresses through their local Internet service provider (ISP). However, firewall and proxy server combinations, which are popular on today’s networks, hide a network’s IP addresses from other hosts on the Internet. These private networks can use any IP addresses they choose, although InterNIC recommends the following IP address blocks for private networks:

Class A networks: 10.x.y.z

Class B networks: 172.16.y.z through 172.31.y.z

Class C networks: 192.168.0.z through 192.16.255.z

Note the following considerations for valid IP addressing:

 

The network ID cannot be 127. The network ID and host ID cannot both be 255.

  The network ID and host ID cannot both be 0. The host ID must be unique for a given network ID.

Computer Names

 

Host Name NetBIOS Name

(Microsoft Windows 2000 & later do not need the NetBIOS names; however, previous version of Windows require NetBIOS to support networking capabilities.)

Host Name

An alias given to a computer on a TCP/IP network to identify it on the network.

Host names are a friendlier way of identifying TCP/IP hosts than IP addresses, and host names can be resolved into IP addresses by host name resolution using a DNS server or hosts files.

Host names can include the characters a–z, A–Z, 0–9, period, and dash (-). To ensure full compatibility with the Domain Name System (DNS), do not use any other special characters in host names.

TIP: To find out the host name of a computer running Windows NT or Windows 2000, type hostname at the command prompt.

NetBIOS Name

NetBIOS: Network Basic Input/Output System, a specification created by IBM and Microsoft that allows distributed applications to access each other’s network services independent of the transport protocol used.

NetBIOS Name: A 16-byte name for a networking service or function on a machine running Microsoft Windows NT. NetBIOS names are a more friendly way of identifying computers on a network than network numbers and are used by NetBIOS-enabled services and applications. NetBIOS names are used by Windows NT applications such as Windows Explorer and Network Neighborhood as well as by the Windows NT net commands.

Each service that is NetBIOS-enabled requires a unique NetBIOS name to identify it on the network. This NetBIOS name consists of a name assigned to the computer during installation, which can be up to 15 characters, along with a 1-byte hexadecimal sixteenth character that identifies the type of service or function. The 15-character name can be the computer name, the domain name, or the name of the user who is logged on.

TIP: To view the NetBIOS names registered for your computer, use the nbtstat command.

Domain Name System (DNS)

A hierarchical system for identifying hosts on the Internet or on a private, corporate TCP/IP internetwork. The Domain Name System (DNS) provides

 

A method for identifying hosts with friendly names instead of IP addresses A distributed mechanism for storing and maintaining lists of names and IP addresses of hosts

 A method for locating hosts by resolving their names into their associated IP addresses so that network communication can be initiated with the host.

The DNS namespace is hierarchical in structure, beginning with the root domain, which branches to top-level domains, then second-level domains, and so on to the individual host name.

For example, the fully qualified domain name (FQDN)

barney.northwind.microsoft.com can be broken down as:

   

Host name: barney Third-level domain: northwind Second-level domain: microsoft Top-level domain: com (commercial domain)

The root domain has a null label and is not expressed in the FQDN.

The DNS is implemented as a distributed database using name servers located at various points on the Internet. Clients called resolvers can perform name lookups by contacting these name servers, which resolve host names into IP addresses.

Each name server on the Internet is responsible for a subset of the DNS namespace known as a zone of authority. Each zone of authority can consist of one or more domains and subdomains.

The most important name servers on the Internet are the dozen or so root name servers, which are responsible for maintaining the infrastructure of the domain name system. These root name servers are maintained mostly by the Internet Network Information Center (InterNIC) and by U.S. military agencies

Although DNS is used mainly for the Internet, large private TCP/IP internetworks can also use DNS internally with their own name servers. The main advantage of doing this is that host names are friendlier than IP addresses. On smaller TCP/IP networks, hosts files can be used instead of DNS, while on Windows NT–based networks, Windows Internet Naming Service (WINS) is often used for NetBIOS name resolution. Windows NT Server has an installable service called the Microsoft DNS Service, which allows Windows NT servers to function as name servers called DNS servers. Windows Internet Name Service (WINS)

A Microsoft Windows NT or Windows 2000 service that dynamically registers NetBIOS names of computers on the network, also resolves these NetBIOS names into IP addresses. Windows Internet Name Service (WINS) is a popular name resolution service on Windows NT networks. On the

Windows 2000 platform, however, DNS is the main name resolution method now used, while WINS is optionally available as a location service for supporting downlevel (Windows NT, Windows 98, Windows 95, and Windows for Workgroups) servers and clients on the network.

WINS works by requiring each NetBIOS host to register its NetBIOS name to IP address mapping on the WINS server by using a process called name registration that is renewed periodically. If the host gets new IP, the database is updated, And when a NetBIOS host is shut down, a name release occurs, removing the host’s associated mapping from the WINS database.

If a client computer (typically a computer running Windows NT W/s, Win98/95) wants to connect to a file server running Windows 2000 or Windows NT, it queries a designated WINS server using a name query, Providing it with the NetBIOS name of the file server it wants to connect to. The WINS server checks its database and responds to the client with the IP address of the desired file server, enabling the client to locate and connect to the file server.

Hosts File

A text file that provides a local method for resolution of fully qualified domain names (FQDNs) into their respective IP addresses on a TCP/IP network. Hosts files are an alternative to DNS servers for name resolution on TCP/IP networks. They are used mainly on small networks or when maintaining a DNS server is impractical.

How It Works You can locate the hosts file using the following paths: • • Microsoft Windows NT or Windows 2000: %SystemRoot%\system32\ drivers\etc\Hosts Microsoft Windows 95 or Windows 98: \%WinDir%\Hosts.sam

Lmhosts File

A text file that provides a local method for name resolution of remote NetBIOS names into their respective IP addresses on a TCP/IP network. It is an alternative to using WINS servers for name resolution on Windows–based networks. Using a WINS server is generally preferable because it reduces administrative overhead.

How It Works: You can find the lmhosts file in the %SystemRoot%\system32\drivers\etc directory in Windows NT and Windows 2000 and in the \Windows directory in Windows 95 and Windows 98.

Each line in the lmhosts file contains the IP address of a NetBIOS computer on the network, followed by the NetBIOS name of the computer. The computer name can be followed by optional prefixes that identify domains and domain controllers and allow entries to be loaded into the NetBIOS name cache at startup. Comments are prefixed with the pound sign (#). Here is an example taken from the sample lmhosts file included with Windows 95:


Name Resolution

The process of resolving the name of a computer on a network into its network address. Name resolution is an important part of network communication because the logical names of hosts on the network must be resolved into their network addresses before communication can take place.

TCP/IP networks running Microsoft Windows operating systems support two name resolution methods: • • NetBIOS name resolution to resolve NetBIOS names into IP addresses. Host name resolution to resolve fully qualified domain names (FQDNs) into IP addresses.

Name Resolution Process

      

DNS Name Cache Hosts File DNS NetBIOS Name Cache WINS Broadcast Lmhosts File

Certain terms are used commonly when we talk about Networking. What are these terms & what do they mean???


 A standard Internet protocol that enables the dynamic configuration of hosts on an Internet Protocol (IP) internetwork.

DHCP is a client-server protocol that uses DHCP servers and DHCP clients. A DHCP server is a machine that runs a service that can lease out IP addresses and other TCP/IP information to any client that requests them. The DHCP server typically has a pool of IP addresses that it is allowed to distribute to clients, and these clients lease an IP address from the pool for a specific period of time, usually several days. Once the lease is ready to expire, the client contacts the server to arrange for renewal.

DHCP clients are client machines that run special DHCP client software enabling them to communicate with DHCP servers. All versions of Windows include DHCP client software, which is installed when the TCP/IP protocol stack is installed on the machine.

DHCP clients obtain a DHCP lease for an IP address, a subnet mask, and various DHCP options from DHCP servers in a four-step process.


Gateways are essentially devices that direct network traffic in some fashion and translate that information.

They are commonly used to provide connectivity between two different protocol stacks that might be running on different systems.


A networking device that is used to extend or segment networks by forwarding packets from one logical network to another. Routers are most often used in large internetworks that use the TCP/IP protocol suite and for connecting TCP/IP hosts and local area networks (LANs) to the Internet using dedicated leased lines.

Routers work at the network layer (layer 3) of the Open Systems Interconnection (OSI) reference model for networking to move packets between networks using their logical addresses (which, in the case of TCP/IP, are the IP addresses of destination hosts on the network).


Any system or device that allows safe network traffic to pass while restricting or denying unsafe traffic. Firewalls are usually dedicated machines running at the gateway point between your local network and the outside world, and are used to control who has access to your private corporate network from the outside—for example, over the Internet. More generally, a firewall is any system that controls communication between two networks.

 A firewall is essentially a kind of router or computer with two network interface cards that filters incoming network packets. This device is often called a packet-filtering router.

Patch Cables

A short cable, usually unshielded twisted-pair (UTP) cabling, that connects a port on a patch panel to a port on a hub or a switch. Patch cables are usually terminated at both ends with RJ-45 connectors.

Patch Cables are of two types: • • Parallel Cable: To connect 2 dissimilar devices, Cross Cable: To connect 2 similar devices.

Parallel/Straight cables

Crossover Cable



Network Interface Cards

An adapter card that plugs into the system bus of a computer and allows the computer to send and receive signals on a network. A network interface card (NIC) is also known as a network adapter card or simply a network card.

NICs can have one or more connectors for cabling to be attached, such as • • • RJ-45 connector for twisted-pair cabling (the most common type) BNC connector for thinnet cabling DB15 connector for connecting drop cables to thicknet cabling.


Any device that can control the flow of electrical signals.

In the context of controlling data flow within a network, the term “switch” is also used to describe a data-link layer device that routes frames between connected networks.

Local area network (LAN) switches: Used to route Ethernet frames over a TCP/IP internetwork; also called Ethernet switches


Also called a repeater hub, the basic networking component used in traditional 10-Mbps Ethernet networks to connect network stations to form a local area network (LAN). Hubs can be used for • Connecting about a dozen computers to form a workgroup or departmental LAN

•    

Connecting other hubs in a cascaded star topology to form a larger LAN of up to roughly a hundred computers

The hub receives signals from each station and repeats the signals to all other stations connected to the hub. Hubs thus perform the function of a repeater and are sometimes called multiport repeaters. Work on Physical Layer. Stations wired into a hub form a star topology.

Troubleshooting & Commands

Network Components

There are 4 components required in a machine to be in a network: • • • • Adapter Client Service Protocol Service

Adapter is the NIC, needed to physically connect to the network.

Client service is used to access server/resource on the network.Eg: Client for Microsoft Networks, Client for NetWare Networks.

Protocol is a set of rules for sending information over a network. Eg: TCP/IP, NetBEUI, IPX/SPX.

Service is background process in an os that provides some specific functionality. Eg: Server service in Microsoft Windows NT and Windows 2000 and File and Printer Sharing for Microsoft Networks in Microsoft Windows 95 and Windows 98, both of which enable sharing of resources over the network.

A Microsoft Windows 95, Windows 98, and Windows 2000 networking component that makes it possible to access file and print services on Windows 95, Windows 98, Windows NT, Windows 2000, Windows for Workgroups, and LAN Manager dedicated servers and peer servers. Client for Microsoft Networks works with any combination of NetBEUI, IPX/SPX-Compatible Protocol, and TCP/IP protocols. Client for Microsoft Networks cannot be used for accessing non-Microsoft servers such as Novell NetWare servers. You must install Client for NetWare Networks to access these servers. Windows 95 and Windows 98 allow you to install more than one client at a time to access different kinds of servers on the network. How It Works: Use the Network utility in Control Panel to install Client for Microsoft Networks on a computer running Windows 95 or Windows 98. Then use the property sheet of Client for Microsoft Networks to configure the computer to either participate in a workgroup or log on to a Windows NT or Windows 2000 domain.


    


 

PING Stands for Packet Internet Groper, a TCP/IP utility that verifies the integrity of a network connection with a host on a TCP/IP network. The ping command is one of the first commands to use to troubleshoot communication problems on a TCP/IP network.

The usual procedure for using ping to troubleshoot a TCP/IP network follows:

• • •

Verify that TCP/IP is installed and running by pinging the local loopback address using ping Ping your own IP address and host name. Ping the IP address of the default gateway for your local network. Ping the IP address of a host on a remote network.


Displays all current TCP/IP network configuration values and refreshes Dynamic Host Configuration Protocol (DHCP) and Domain Name System (DNS) settings. Used without parameters, ipconfig displays the IP address, subnet mask, and default gateway for all adapters.

Syntax: Ipconfig


/all : Displays the full TCP/IP configuration for all adapters. Without this parameter, ipconfig displays only the IP address, subnet mask, and default gateway values for each adapter. Adapters can represent physical interfaces, such as installed network adapters, or logical interfaces, such as dial-up connections. /renew [Adapter] : Renews DHCP configuration for all adapters (if an adapter is not specified) or for a specific adapter if the Adapter parameter is included. This parameter is available only on computers with adapters that are configured to obtain an IP address automatically. /release [Adapter] : Sends a DHCPRELEASE message to the DHCP server to release the current DHCP configuration and discard the IP address configuration for either all adapters (if an adapter is not specified) or for a specific adapter

• •

Few Troubleshooting Steps

    

Check the IP Address. Check the Subnet mask, default gateway, DNS. Ping loopback ip, self ip, gateway, then remote machine. Disable firewalls & IEEE authentication. Drivers & other things like lan cable, port etc.

Going online: Connecting to a collection of interconnected computers on a network.

• • • • • • • •

Do banking. Pay bills. Buy groceries. Book vacation travel. Send messages. Participate in discussions. Do research. Play games.

Network: A collection of computers, display terminals, printers, and other devices linked either by physical or wireless means.

Computer Networking • • Internet: A world-wide network connecting millions of computer networks for the purpose of exchanging data and communications using special rules of communication. internet: (lower case i) Any network connecting two or more computer networks.

Starting of Networking

1966: ARPA (Advanced Research Projects Agency) State Defense Department’s research organization. – – – – Focused major development effort on computer networking. ARPA’s Goal: To promote research in advanced future technologies by funding university and industry research proposals. Result: Thousands of databases became available to the public.

Types of connections of computers into networks: Physical versus Wireless connections

The first type: The Physical Connection. Physically connect computers together. Use of wires or optical cables. The connections are called network links. Three most common physical links: Twisted pair Coaxial cable Fiber-optic cable

1:- Twisted pair • Two wires twisted together. – • Makes them less susceptible to acting like an antenna and picking up radio frequency information or appliance noise.

Telephone Company uses twisted-pair copper wires to link telephones.

2:- Coaxial cable • Also two wires: – – – – One of the wires is woven of fine strands of copper forming a tube. The wire mesh surrounds a solid copper wire that runs down the center. Space between has a non-conducting material. Makes them more impervious to outside noise.

3:- Fiber-optic cable

• •

Light is electromagnetic. Can transmit more information down a single strand. – It can send a wider set of frequencies.

Each cable can send several thousand phone conversations or computer communications.

Second type of connections of computers into networks: Wireless connections

• •

The link is made using electromagnetic energy that goes through space instead of along wires or cables. Three types of wireless communications commonly used in networking: – – – Infrared Radio frequency Microwave

1:- Infrared

• • • •

Commonly used in TV and VCR remote controls. Use infrared frequencies of electromagnetic radiation that behave much like visible light. Must be in the line of sight. Often used to connect keyboards, mice, and printers.

2:- Radio frequency

Uses radio frequencies. – Function even though line of sight is interrupted.

Not commonly used because of the possible interference from other sources of electromagnetic radiation such as old electric drills and furnace motors.

3:- Microwave

• • • Often used to communicate with distant locations. Must be line of sight. Satellite communications use microwaves.

Properties of Transmission

Five basic properties of both the physical and wireless links: 1. Type of signal communicated (analog or digital). 2. The speed at which the signal is transmitted (how fast the data travels). 3. The type of data movement allowed on the channel (one-way, two-way taking turns, two-way simultaneously). 4. The method used to transport the data (asynchronous or synchronous transmission). 5. Single channel (baseband) and multichannel (broadband) transmission.

Type of signal communicated (analog or digital).


Those signals that vary with smooth continuous changes. – A continuously changing signal similar to that found on the speaker wires of a high-fidelity stereo system.


Those signals that vary in steps or jumps from value to value. They are usually in the form of pulses of electrical energy (represent 0s or 1s).

The speed at which the signal is transmitted (how fast the data travels).

• In digital systems: Speed is measured in...

Bits per second (bps). • The number of bits (0’s and 1’s) that travel down the channel per second.

Baud rate • • The number of bits that travel down the channel in a given interval. The number is given in signal changes per second, not necessarily bits per second.

MODEM - Modulator Demodulator

Outgoing: Converts binary data from computer (digital) into telephone compatible signals (analog).

Incoming: Converts telephone signal (analog) into binary data for the computer (digital).

Can be an external or internal device (usually a “card”).

The type of data movement allowed on the channel.

• • •

Simplex transmission - One way transmission. Half-duplex transmission - Flows only one way at a time. Full-duplex transmission - Two-way transmission at the same time.

4. The method used to transport the data.

Two types of data transmission, each requiring a different modem.

a:-Asynchronous transmission -

Information is sent byte by byte. Cheaper and more commonly used.

b:-Synchronous transmission Data is sent in large blocks rather than in small pieces. Preceded by special information, concerning error detection and block size. These modems are expensive but very fast.

Single channel versus multichannel transmission

Channel - A path of a signal.

Single channel - Capable of only sending/receiving one signal at a time. – Phone line: Single line = single phone call at a time.

Multichannel - Capable of more than one channel at a time. – Fiber-optic cable, microwaves, Satellite transmissions

How is it possible to measure the capacity of communications links?

Bandwidth: Digital – – – Number of bits per second (bps) that can be sent over a link. The wider the bandwidth, the more diverse kinds of information can be sent. Simplest is voice, most sophisticated is moving videos.

Bandwidth: Analog – – The difference between the highest and lowest frequencies that can be sent over an analog link (like phone lines). Measurement is given in hertz (Hz).

For both: The wider the bandwidth, the more information can flow over the channel.

Node: The generic name given to all devices hooked up to a network.

• •

Each node must have a unique address assigned to them by the network. Networks are either direct-connected or those that are not directly linked. – Direct-connected network: Those whose nodes have direct connections through either physical or wireless links. • Point-to-point: Simplest version of direct-connected network. Connecting two computing systems. » – Example of point to point: Home to ISP.

Example of a network that is not directly linked: Internet.

The bus network –

A continuous coaxial cable to which all the devices are attached.

• All nodes can detect all messages sent along the bus.

The ring network • • Nodes linked together to form a circle. A message sent out from one node is passed along to each node in between until the target node receives the message.

The star network –

• •

Each node is linked to a central node. All messages are routed through the central node, who delivers it to the proper node.

The tree network - (hierarchical network)

Looks like an upside-down tree where end nodes are linked to interior nodes that allow linking through to another end node.

LAN (Local Area Network) • • A collection of nodes within a small area. The nodes are linked in a bus, ring, star, tree, or fully connected topology network configuration.

Benefits of LANs: – Sharing of hardware resources.

– – – – Sharing of software and data. Consolidated wiring/cabling. Simultaneous distribution of information. More efficient person-to-person communication.

MAN (Metropolitan Area Network) • • Consists of many local area networks linked together. Span the distance of just a few miles.

WAN (Wide Area Network) • • Consists of a number of computer networks including LANs. Connected by many types of links.

Security of a Network

Enterprise and intranet networks: Corporations, government agencies, and other organizations have created their own internal networks.

Firewall: A set of programs that monitor all communication passing into and out of a corporation’s intranet. • Helps prevent, but doesn’t eliminate, unauthorized access.

General Networking
1. Q: What is an IP Addresses? 2. Q: What is Dynamic IP Addressing? 3. Q: What is Static IP Addressing? 4. Q: How Do I Checking My IP Address in Windows 98 / SE / ME / 2000 / XP ?? 5. Q: How Do I Checking My IP Address in Linux? 6. Q: How to setup a Static IP Address on Windows 98 / SE / ME? 7. Q: How to setup a Static IP Address on Windows 2000 / XP? 8. Q: How to Releasing an IP Address in Windows 98 / SE / ME? 9. Q: How to Releasing an IP Address in Windows 2000 / XP? 12. Q: How to Sharing Folder on Windows 98SE / ME / 2000 / XP? 13. Q: How to Sharing Drives on Windows 98 / SE / ME / 2000 / XP? 14. Q: How to Accessing Other Computers Shared Files on Windows 98/SE/ME/ 2000/XP? 15. Q: How to Sharing Printers on Windows 98 / SE / ME / 2000 / XP? 16. Q: How install a Network Printer for Windows 98/ SE / ME/ 2000 /XP? 17. Q: How to Connecting to Internet on Windows 98 / SE / ME ? 18. Q: How to Accessing the Internet using Windows 2000 / XP?

1. Q: What is an IP Addresses?

IP Stands for Internet Protocol. An IP Address is the identifier where other computers on the network can contact your computer, when you are connected to the network using the TCP/IP protocols. The format of IP addresses are 32bit numerical addresses in 4 groups of 3. It is ranged from 0-255. For example: This number allows your computer to be unique on the same network, and able to communicate with other computers on the network.

2. Q: What is Dynamic IP Addressing?

Dynamic IP Addressing is where the computer will automatically be assigned a new IP Address. This IP Address will be unique to the network that it is working on, and should not be the same as any other computer on the same network.

3. Q: What is Static IP Addressing?

Static IP Addressing is where the computer will have a preconfigured IP Address. This Address will never change, and will always be the same. This scheme should be used if you want to keep the same settings on each computer all the time. If the subnet of the network changes (subnet is the first 3 groups of the IP) the subnet of the static computer must also change.

4. Q: How Do I Checking My IP Address in Windows 98 / SE / ME / 2000 / XP

Click Start and click Run

Type “Command” in the run prompt, Click OK

A Dos Command prompt will open. Type in ipconfig and press Enter

Your IP Address will Display, along with the Subnet Mask, and your Gateway

5. Q: How Do I Checking My IP Address in Linux?

A: At the command line type /sbin/ifconfig and you will get a listing of information. Your IP is shown after inet addr.

6. Q: How to setup a Static IP Address on Windows 98 / SE / ME?

Right Click on “Network Neighborhood” and click Properties”

Click on “TCP/IP” for the network adapter you want to set IP addresses for

Click on “Specify an IP address” Type in the IP Address you wish to use. (192.168.XXX.XXX is very standard for home networks) Click on the Subnet mask, and if you know the subnet mask you want to use, type it in, otherwise it should fill in with “” which is very standard for subnet masks.


Click on the “Gateway” tab, and add in a gateway if you need to. Then click OK

To save the changes you must restart, so click “YES” 7. Q: How to setup a Static IP Address on Windows 2000 / XP

Right click My Network Places and click Properties.


Find and “Double Click” the Local Area Connection for the Network adapter you want to Set IP’s for.

Click Properties button

Click (Highlight) “Internet Protocol (TCP/IP)” and click “Properties”

Click “Use the following IP address” Type in the IP Address you wish to use. (192.168.XXX.XXX is very standard for home networks) Click on the Subnet mask, and if you know the subnet mask you want to use, type it in, otherwise it should fill in with “” which is very standard for subnet masks. Click on the Default gateway and fill that in. If you know the DNS you are going to use, fill it in otherwise leave it blank. Then click OK.

To check that everything is Correct, Click on “Support” and the information you typed in should appear.

8. Q: How to Releasing an IP Address in Windows 98 / SE / ME?

Click Start, then click Run

Type “winipcfg” and click OK

Select the Network adapter you want to release IP’s for.

Click “Release” button

Your IP Address should turn to


If you Click Release, and an error saying “IP Address for adapter is already released” then you do not need to release any more, Try “Renewing your IP” 9. Q: How to Releasing an IP Address in Windows 2000 / XP?

Click Start, then click Run

Type Command and click OK

Type “ipconfig /release” and press Enter


Your IP Address should turn to . To Renew your address check Renewing IP Address.

If you receive an Error “The operation failed as no adapter is in the state permissible for this operation.” Then you might need to set your Network adapter to obtain your “IP Address Automatically”.

DISCUSSION Whenever clients report difficulties accessing IP services, it is good practice to verify IP connectivity at the client and at the server. Even if the client connected successfully in the past, many different things could cause unsuccessful attempts at any time, such as:

     

TCP/IP settings accidentally changed. Routers down. DNS services down. Duplicate IP address appears on the network. Address server (DHCP, BootP) not functioning/not accessible. Corruption is some system files or TCP/IP preference files.

Ping Utilities Testing IP connectivity is often done using utilities that send ping packets. Ping packets are simply small packets from one host to another, that request a response from the recipient. Many ping utilities are available for free download on the Internet. One favorite is MacTCP Watcher. A ping utility is invaluable when troubleshooting IP connections, and the following suggestions are assuming that some ping utility is available. If no ping utility is available, then use whatever IP applications are at hand; the simpler the better. Remember that the device you are attempting to contact has to support the service that the client software is trying to reach. You may be able to use a Web browser to test a connection with another Macintosh that has Personal Web Sharing enabled, but you cannot use it to test a connection to your router. Here is a suggested troubleshooting path for isolating difficulties with a client trying to connect to the host. Ping the host using its Domain name If pinging succeeds, then there is no fault with the client or the IP connection between client and host. Your next step would be to check the applications at client and host, and look for faults there (Web server, file server, mail client, and so forth).

If pinging fails, it could indicate a fault with the routers or DNS servers, not necessarily with the workstation itself. Go on to the next step. Ping device on local subnet using IP address Pinging a device on your same subnet using its IP address does not require routers or DNS servers to be successful, so it verifies that each device is able to communicate, at least on its own subnet, using TCP/IP. Important: be sure that the workstation you are attempting to ping has its IP stack (protocol set) initialized. Most Macintosh computers do not initialize the IP stack until an application that uses IP is opened. On the Macintosh you'll be pinging, open an IP application, such as the Web browser or a ping utility, to initialize the stack before attempting the ping. You can determine which other devices are on the same subnet by checking the physical connections (are they connected to the same hub? or same bus?) or by checking their IP addresses (are the network portions of the IP addresses identical? You have to consider the IP address AND the subnet mask to determine this).

    

If pinging a device on the same subnet is successful, you have verified that the computer's IP connections are working, but there still may be some fault with external network devices, such as routers, DNS servers. Continue on with the next step. If pinging a device on the same subnet fails, then you must check carefully the local software and hardware configurations.

Here are some tips on how to do that: See if any other device on same subnet can ping other devices. This lets you know if the local network is functioning, and if basically the IP addresses have been set up correctly. If server addressing is being used, see if you can test with a manual address, to see if the fault is with communications between the client and address server. Check TCP/IP configuration carefully; compare them with that of a Macintosh that is working properly: verify link being used, IP address, subnet mask, and router information, whether "802.3" is checked (Advanced mode)

NOTE: Usually 802.3 should be UN checked; only check it if ALL devices are using 802.3 for TCP/IP communications. - Check network connections:

      

make sure they are not loose. swap out network hardware with a working computer. test AppleTalk on the same link (network interface) if possible.

- If none of the above fixes the issue, try: resetting PRAM. tossing TCP/IP preferences and MacTCP DNR, and reconfiguring. turning off non-MacOS extensions. reinstalling Open Transport, or perform a clean installation of system software.

Ping router port on same subnet The workstation's TCP/IP panel may be configured with a router address. (This should be the router port which is on the same subnet as the workstation itself.) All communications with devices not on the same subnet as the workstation must pass through this router, so if it is not available, your client will not be able to talk to anyone outside the subnet.

  

Using a ping utility, attempt to ping the router port. If pinging the router is successful, go to next step. If pinging the router fails, see the network administrator, or whoever manages the router, and report the issue.

Ping DNS server Whenever a host attempts to make a connection using a domain name, that name must first be resolved to an IP address. The name is sent to the first DNS server listed in the TCP/IP control, and if that server does not respond, it will be sent to the second, the third, and so on. Try pinging the DNS servers listed.

If pinging the DNS server succeeds, MacTCP Watcher lets you do a DNS Lookup; see if you can resolve a domain name (try several names in different domains, such as www.apple.com, www.cornell.edu, phc.mpr.org). If resolving names fails, it is possible that the server is down (or the address is not that of a DNS server after all). Verify the information with the network administrator. If pinging the DNS server fails, report it to the network administrator. In the meantime, you can reconfigure your TCP/IP control panel with an address of a working DNS server; check the configurations of other devices on the network who are able to resolve names successfully.

12. Q: How to Sharing Folder on Windows 98SE / ME / 2000 / XP?


Double click “My computer”

Double Click the Drive where the folder that you want to share is located.

Right Click on the folder you want to share, and click “Properties”

Click on the sharing tab, then “If you understand the risk but still want to share the root of the drive, click here”


Click “Share this folder on the network” and specify the name you want the folder to be seen as on the network.

A Hand should appear under the folder you wanted to share letting you know that it is shared on the network.

13. Q: How to Sharing Drives on Windows 98 / SE / ME / 2000 / XP?

Right click on “My Computer” and click “Properties”

Right click on the drive you want to share and click “Properties”

click on the Sharing tab “If you understand the risk but still want to share the root of the drive, click here”


Click on “Share this folder on the network” and specify what you want your shared folder to be viewed as.

A hand should appear under the drive you wanted to share. This lets you know that it is shared on your network

14. Q: How to Accessing Other Computers Shared Files on Windows 98/SE/ME/ 2000/XP? Find the IP Address of the computer you want to access

Click Start, and then click Run


Type “\\” and the IP address of the computer you want to access. (Format is “XXX.XXX.XXX.XXX”)

All the files that the computer you are trying to access will open in a new window.

An Alternate way to do the same thing is to find the Computer Name of the computer you are trying to access. And typing “\\______” with the computer name in the blank

All the files that the computer you are trying to access will Open in a new window. 15. Q: How to Sharing Printers on Windows 98 / SE / ME / 2000 / XP?


Click “Start” and click ‘Printers and Faxes”

Right click on the printer you want to share and click “Properties”

click the “Sharing” tab, and click “Share the printer” then specify the name that you want the printer to be seen as on the network. Then click “OK”

A hand should appear under the printer you want to share. 16. Q: How install a Network Printer for Windows 98/ SE / ME/ 2000 /XP?

Click Start and click on Printers and Faxes.

The Printers and Faxes window should open, on the left side there should be an Add a Printer button under Printer Tasks. Click on Add a Printer

The Add Printer Wizard should appear, click Next to proceed


Select “A network printer or a printer attached to another computer” and click Next

Click “Browse for a printer”, unless you know the computer name(or IP address) of the printer, and the exact printer name. Or the printer is at a location that can be connected to through the internet. And click Next


Browse through your network and select the printer that you want to add, Highlight it, and click Next Browse through your network and select the printer that you want to add, Highlight it, and click Next



Click Yes to proceed


Unless you want this to be your default printer, click NO, otherwise click YES and click Next


Click Finish to finish the network installation


The printer should now be installed on your computer.

**Note** You may need to install drivers for the printer you want to install, so make sure you have them available before trying to install any printer. 17. Q: How to Connecting to Internet on Windows 98 / SE / ME?


Double Click Internet Explorer

The Internet Connection Wizard Should open(If this does not open and Internet Explorer Opens up, skip to Section 7) Click “I want to set up my Internet Connection Manually, or I want to connect through a local area network(LAN)” click Next

Click “I connect through a local area network(LAN)” Click Next


Click “Automatic discovery of proxy server(recommended)” Click next

Unless you want to setup your Email(you can do this separately later) Click NO, and click Next.

Click the box, and click Finish You should be on the internet, If a website does not occur Try to Release IP, then Renew IP, and try to Ping your gateway. 18. Q: How to Accessing the Internet using Windows 2000 / XP?

Double Click on Internet Explorer


The New Connection Wizard might open(If this does not happen, skip to Step 7) Click Next

Click “Connect to the Internet” and click Next

Click “Set up my connection manually”

Click “Connect using a broadband connection that is always on”

Click Finish


You should be on the internet, If a website does not occur Try to Release IP, then Renew IP, and try to Ping your gateway.

Troubleshooting TCP/IP Networks The purpose of this section is to give general tips on troubleshooting your TCP/IP LAN or Internet Connection The basics for troubleshooting are: 1. 2. 3. 4. Make sure you have the same IP scheme (e.g. 192.168.0.x). Make sure you have the same Subnet Mask, Gateway, and DNS IP addresses Make sure you can ping the other computer's by IP address Make sure you can ping the other computers by Name

5. 6. 7. 8. 9. 10. Make sure you have the same workgroup name (watch for trailing spaces) For troubleshooting purposes, uninstall any 3rd party firewall software and turn off XP's built in one. You can always add more complexity after you get it working. With Windows2000 or XP, make sure you have the same username and password as the person logging onto the other computers. The default setting for XP Pro is to require a password for network access. Apply the registry edit to fix the browsing delay from Widnows2000 and XP to Win9x computers. http://www.onecomputerguy.com/windowsxp_tips.htm#browsing_delay. More details about how to network XP can be found at: http://www.onecomputerguy.com/networking/xp_network.htm Basically keep things simple. Remove any unnecessary firewalls, protocols or other configurations the complicate the troubleshooting process. You can add them back in later after you get things working. If you are having difficulty make a network connection

• • • •

Try PINGing other computer(s) on your network both by IP address and Name This is to test if you have basic TCP/IP connectivity. Without success here, you are likely not to get much farther. First use a computer's IP address. If you are connecting to the Internet, try pinging the IP address of your external DNS server. The syntax is: PING IP_Address. An example would be PING Try Pinging Yourself

• •

This does not mean using your own IP address Either type: PING localhost or PING

A good response ensures the loopback in the local machine can be reached.

Submitted by Wilbur Haven If you do not get a reply, your network configuration, modem, Ethernet card, or cabling is probably at fault Triple check all your network settings. If you have Win9x, you can run WINIPCFG to get a graphic of your TCP/IP settings. Click on the More Info tab to bring up a screen similar to the one below.


• • • • •

If you have Windows2000 or XP, open up a command window (Start / Run / CMD), then run IPCONFIG /ALL. This will give a text display of all the IP information for any network adapters. If you have a network adapter, make sure that the adapter is set up correctly. Also check to see if any link status lights on your adapter are lit. If you are on a local LAN, see if you can use another known working computer's network drop, cabling, and network card. Make sure your Dial-Up Network settings are all correct. It is easy to miss an item.

If your PING works but you are having problems finding sites on the Internet

• • • •

Try PINGing a name rather than an IP address. This will determine if your DNS entry is correct or working. For example: PING www.yahoo.com If this works, then likely your web browser is misconfigured. Make sure you do not have an incorrect proxy server setting in your Web Browser

If you can't Ping a Computer Name

• •

Check the DNS IP address in your Network or Dial-Up Icon's setup If you are only using an ISP and not connected to a local LAN, you only need a DNS entry in the Dial-Up Icon.

If you are on a LAN but cannot connect to any other devices

• • • • • •

If you can ping all the other computers on your network but are not allowed access: Make sure you have the same username and password defined on any NT based computer (NT 4, Windows2000 and XP), that are logging into the other computers. Try connecting to the computer using Start \ Run and enter \\Servername where Servername is the name of the server you want to connect to. Add the Computer and it's IP address to the LMHOSTS file. This is a straight text file that resides in the Windows directory (for Win9x) or the Windows\System32\drivers\etc directory (for Windows2000 or XP) and has the format IP_Address Computer_Name Don't rely on the Network Neighborhood to always show you a list of computers. Browsing is fairly complicated issue and has a lot of places for failure. If you need to have resources available, create shortcuts on your desktop instead If you have Win95, make sure you get the Winsock update from Microsoft before connecting to a Windows2000 or XP computer.

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