Ring Topology

Ring Topology
In the ring topology, each computer is connected directly to two other computers in the network. Data moves down a one-way path from one computer to another, as shown in Figure 1.7. The good news about laying out cable in a ring is that the cable design is simple. The bad news is that, as with bus topology, any break, such as adding or removing a computer, disrupts the entire network. Also, because you have to “break” the ring in order to add another station, it is very difficult to reconfigure without bringing down the whole network. For this reason, the physical ring topology is seldom used.

Note:

Although its name suggests a relationship, Token Ring does not use a physical
ring topology. It instead uses a physical star, logical ring topology (and runs at
speeds of either 4Mbps or 16Mbps). You will learn more about logical topologies
later in this chapter.

Example:

A typical ring topology

 A few pros and many cons are associated with a ring topology. On the pro side, the ring topology is relatively easy to troubleshoot. A station will know when a cable fault has occurred because it will stop receiving data from its upstream neighbor.
On the con side, a ring topology has the following characteristics:

• Expensive, because multiple cables are needed for each workstation.
• Difficult to reconfigure.
• Not fault tolerant. A single cable fault can bring down the entire network.

Read More

Star Topology

Star Topology
Unlike those in a bus topology, each computer in a star topology is connected to a central point by a separate cable or wireless connection. The central point is a device known by such names as
hub, MAU, concentrator, switch, and access point, depending on the underlying technology.

Real World Scenario
    A bus sounds good, but . . .

Despite the simplicity of the bus topology, there are some inherent disadvantages to this design. For example, what happens if the wire breaks or is disconnected? Neither side can communicatewith the other, and signal bounce occurs on both sides. The result is that the entire network is down. For this reason, bus topologies are considered to have very little fault tolerance. Sometimes, because a cable is inside a wall, you cannot physically see a break. To determine if a break has occurred, you can use a tool known as a Time Domain Reflectometer, or TDR (also called a cable tester). This device sends out a signal and measures how much time it takes to return. Any break in the cable will cause some portion of the signal to return prematurely, thus indicating the presence of, and the distance to, a break in the cable. Programmed with the specifications of the cable being tested, it determines where the fault lies with a high degree of accuracy.We’ll discuss cable testers in Chapter 6, “Wired and Wireless Networks.”

 Although this setup uses more cable than a bus, a star topology is much more fault tolerant than a bus topology. This means that if a failure occurs along one of the cables connecting to the hub, only that portion of the network is affected, not the entire network. Depending on the type of device at the other end of that cable, this may affect only a single device. It also means that you can add new stations just by running a single new cable. Figure 1.6 shows a typical star topology.

Example:

A typical star topology with a hub

The design of a star topology resembles an old wagon wheel with the wooden spokes extending from the center point. The center point of the wagon wheel would be considered the hub.
Like the wagon wheel, the network’s most vulnerable point is the hub. If it fails, the whole system collapses. Fortunately, hub failures are extremely rare.

As with the bus topology, the star topology has advantages and disadvantages. The increasing
popularity of the star topology is mainly due to the large number of advantages, which
include the following:

• New stations can be added easily and quickly.
• A single cable failure won’t bring down the entire network.
• It is relatively easy to troubleshoot.
• The disadvantages of a star topology include the following:
• Total installation cost can be higher because of the larger number of cables, but prices are constantly becoming more and more competitive.
• It has a single point of failure (the hub, or other central device). There are two subtle special cases for the star topology, the point-to-point link and the wireless

access point. If you think of a point-to-point connection as one spoke of a star-wired network,
with either end device able to play the role of the hub or spoke device, then you can begin
to see the nature of any star-wired topology. What about when there is no wire, though? It takes
a firm understanding of what the devices making up the wireless network are capable of to be
able to categorize the wireless topology. Wireless access points, discussed in detail in Chapter
6, are nothing more than wireless hubs or switches, depending on capability, that are able to act
as wireless bridges by establishing a wireless point-to-point connection to another wireless

access point. Either use is reminiscent of the wired star/point-to-point topologies they emulate.

Read More

Bus Topology

Bus Topology
In a bus topology, all computers are attached to a single continuous cable that is terminated at both ends, which is the simplest way to create a physical network. Originally, computers were attached to the cable with wire taps. This did not prove practical, so drop cables were used to

attach computers to the main cable. In 10Base-2 Ethernet, no drop cables are used, but instead, a “T” is inserted in the main cable wherever a station needs to connect. Figure 1.5 shows an example of a bus network. Notice how the cable runs from computer to computer with several bends and twists.

Example:

An example of a physical bus topology

     When communicating on a network that uses a bus topology, all computers see the data on the wire. This does not create chaos, though, because the only computer that actually accepts the data

is the one to which it is addressed. You can think of a bus network as a small party. David is already there, along with 10 other people. David would like to tell Joe something. David yells out, “Joe! Will

you grab me a cup of coffee, please?” Everyone in the party can hear David, but only Joe will respond. A star network with a hub, which you’ll read about later, also operates in this manner.

As with most things, there are pros and cons to a bus topology. On the pro side, a bus

 topology has the following characteristics:

•  Is simple to install
• Is relatively inexpensive
• Uses less cable than other topologies

The following characteristics describe the con side of a bus topology:

• Is difficult to move and change
• Has little fault tolerance

 (a single fault can bring down the entire network)

• Is difficult to troubleshoot

Read More

Physical Topologies

Physical Topologies:
A topology is basically a map of a network. The physical topology of a network describes the layout of the cables and workstations and the location of all network components. Often, physical
topologies are compared to logical topologies, which define how the information or data flows within the network. The topologies are usually similar. It is important to note, however, that a network can have one type of physical topology and a completely different logical topology. This was discussed earlier in the sidebar “Physical vs. Logical Concepts.” 

   The cables or connections in a physical topology are often referred to as network media (or physical media). Choosing how computers will be connected in a company’s network is critical.
A wrong decision in the physical topology makes the media difficult to correct because it is costly and disruptive to change an entire installation once it is in place. The typical organization changes the physical layout and physical media of a network only once about every 10 years, so it is important to choose a configuration that you can live with and that allows for growth.

      In the next section, we’ll look at physical media. In the following sections, we’ll look at the  five most common topologies:

• Bus
• Star
• Ring
• Mesh

Read More

Peer-to-Peer vs. Client/Server Architecture

Peer-to-Peer vs. Client/Server Architecture
As you learned earlier in this chapter, the purpose of networking is to share resources. How this
is accomplished depends on the architecture of the network operating system software. The two
most common network types are peer-to-peer and client/server.

If you were to look at an illustration of a group of computers in a LAN, it would be impossible to determine if the network was a peer-to-peer or a client/server environment. Even a videotape of this same LAN during a typical workday would reveal few clues as to whether it is peer-to-peer or client/server. Yet, the differences are huge. Since you can’t see the differences, you might guess correctly that they are not physical but logical.

Physical vs. Logical Concepts
Throughout this book, you’ll see us refer to physical and logical networking topics. Generally speaking, when we’re referring to the physical aspects of a network, we’re referring to some aspect of the network that you can touch or that has physical substance (like electrons, electrical pulses, or the way cables are run). That is, they exist in the physical world. Logical concepts, on the other hand, are more imaginary and esoteric and deal with things like how data flows in a network. So, when we’re describing something as either physical or logical in nature, you’ll understand how those terms apply.

Peer-to-Peer Network
In peer-to-peer networks, the connected computers have no centralized authority. From an authority viewpoint, all of these computers are equal. In other words, they are peers. If a user
of one computer wants access to a resource on another computer, the security check for access rights is the responsibility of the computer holding the resource. Each computer in a peer-to-peer network can be both a client that requests resources and a server
that provides resources. This is a great arrangement, provided the following conditions are met: 
 

• Each user is responsible for local backup.
•   Security considerations are minimal.
• A limited number of computers are involved. 

Networks that run Windows 95/98 as their network operating system and networks using Windows NT, 2000, or XP in a workgroup are considered peer-to-peer networks. Figure 1.3 shows an example of a peer-to-peer network. Peer-to-peer networks present some challenges. For example, backing up company data becomes an iffy proposition. Also, it can be difficult to remember where you stored a file. Finally, because security is not centralized, users and passwords must be maintained separately on each machine, as you can see in Figure 1.3. Passwords may be different for the same users on different machines 

(or for different resources on Windows 9x machines).

Client/Server Network
In contrast to a peer-to-peer network, a client/server network uses a network operating system designed to manage the entire network from a centralized point, which is the server. Clients make requests of the server, and the server responds with the information or  ccess to a resource.

Example:

A peer-to-peer network

Client/server networks have some definite advantages over peer-to-peer networks. For one thing, the network is much more organized. It is easier to find files and resources because they are stored on the server. Also, client/server networks generally have much tighter security. All usernames and passwords are stored in the same database (on the server), and individual users can’t use the server as a workstation. Finally, client/server networks have better performance and can scale almost infinitely. It is not uncommon to see client/server networks with tens of thousands of workstations. Figure 1.4 shows a sample client/server network. Note that the server now holds the database of user accounts, passwords, and access rights.
Note that today’s networks are very often hybrids of the peer-to-peer model and the client/server model. Clients of early Novell NetWare networks, for example, had no ability to share  their resources, not that they had many worth sharing, for the most part. Conversely, today’s Microsoft and Apple networks, for example, have well-defined servers. They also allow the simultaneous sharing of resources from lesser devices that run what are considered workstation operating systems, which are capable of fewer inbound connections but are running the server service nonetheless. Purists shun the less organized mixture of this resource sharing among servers and clients alike, but the reality is that most networks would be worse off for losing this capability.

Example:

A client/server network

Read More

Host, Workstation, and Server

Host, Workstation, and Server

Networks are made up of lots of different components, but the three most common network

entities are the host, workstation, and server. For the Network+ exam, you need a good understanding

of these three primary components of a network. Each one of these items can be found

on most networks.

Understanding Workstations

In the classic sense, a

workstation

is a powerful computer used for drafting or other math-intensive

applications. The term is also applied to a computer that has multiple central processing

units (CPUs) available to users. In the network environment, the term

workstation

normally

refers to any computer that is connected to the network and used by an individual to do work.

It is important to distinguish between workstations and clients. A

client

is any network entity

that can request resources from the network; a workstation is a computer that can request

resources. Workstations can be clients, but not all clients are workstations. For example, a

printer can request resources from the network, but it is a client, not a workstation.

Understanding Servers

In the truest sense, a server does exactly what the name implies: It provides resources to the clients

on the network (“serves” them, in other words). Servers are typically powerful computers

that run the software that controls and maintains the network. This software is known as the

network operating system.

Servers are often specialized for a single purpose. This is not to say that a single server can’t

do many jobs, but, more often than not, you’ll get better performance if you dedicate a server

to a single task. Here are some examples of servers that are dedicated to a single task:

•  File Server

Holds and distributes files.

•  Print Server

Controls and manages one or more printers for the network.

•  Proxy Server 

Performs a function on behalf of other computers. (Proxy means “on behalf of.”)

•  Application Server

Hosts a network application.

•  Web Server

Holds and delivers web pages and other web content using the Hypertext Transfer Protocol (HTTP).

• Mail Server

Hosts and delivers e-mail. It’s the electronic equivalent of a post office.

•   Fax Server 

Sends and receives faxes (via a special fax board) for the entire network without the need for paper.

•  Remote Access Server 

Listens for inbound requests to connect to the network from the outside.
Remote access servers provide remote users (working at home or on the road) with a connection
to the network, either via modems or an IP connection.

• Telephony Server

 Functions as a “smart” answering machine for the network. It can also perform

call center and call-routing functions.

Notice that each server type’s name consists of the type of service the server provides (remote

access, for example) followed by the word server, which, as you remember, means to serve.

Regardless of the specific role (or roles) these servers play, they should all have the following

in common:

_ Hardware and/or software for data integrity (such as backup hardware and software)

_ The capability to support a large number of clients

Figure 1.1, earlier in this chapter, shows a sample network. Physical resources, such as harddrive

space and memory, must be greater in a server than in a workstation because the server

needs to provide services to many clients. Also, a server should be located in a physically secure

area. Figure 1.2 shows a sample network that includes both workstations and servers. Note that

there are more workstations than servers because a few servers can serve network resources to

hundreds of users simultaneously.

Example:

A sample network including servers and workstations

Understanding Hosts

The term host covers pretty much every other networking device, but it can also refer to a workstation

and server and is most commonly used when discussing TCP/IP-related services and

functions. In fact, a host, in TCP/IP terms, is any network device that has an IP address. Workstations,

servers, and any other network device (as long as it has one or more IP addresses) can

all be considered hosts. In conversation, you may also hear the word host used to describe any

minicomputer or server. For the Network+ exam, however, you should stick to the classic definition

used here (i.e., workstations, servers, and other network devices).

The term host comes from the era when the only intelligent devices on the network were

mainframes, which were commonly referred to as hosts regardless of TCP/IP functionality.

Nearly all other devices were known as dumb terminals, but no other device had intelligence,

only the mainframe. As TCP/IP came into the picture, only the mainframes, or hosts, received

IP addresses. This is the same era that produced the term gateway to refer to any layer 3 intermediate

device, such as a router. Just as the term gateway remains in common use today, such

as in the very common term default gateway, the term host is still used, but its use is much

broader now that nearly every end and intermediate device is intelligent and has at least one IP

address, making them hosts.

Read More

Wide Area Network

Wide Area Network:

Chances are you are an experienced wide area network (WAN) user and don’t even know it. If you have ever connected to the Internet, you have used the largest WAN on the planet. A WAN is any network that crosses metropolitan, regional, or national boundaries. Most networking professionals define a WAN as any network that uses routers and public network links. The Internet fits both definitions.

       WANs differ from LANs in the following ways:

_

                WANs cover greater distances.

_

                WAN speeds are slower.

_

                WANs can be connected on demand or permanently connected; LANs have permanent

                connections between stations.

_

                WANs can use public or private network transports; LANs primarily use private network

                transports.

_

                WANs can use either full- or half-duplex 

communications. LANs have typically used halfduplex

                communications, although many local area networks today use full-duplex communications

                (see the sidebar “Full-Duplex vs. Half-Duplex Communications”).

The Internet is actually a specific type of WAN. The Internet is a collection of networks that

are interconnected and, therefore, is technically an internetwork

( Internet is short for the word internetwork ).

                A WAN can be centralized or distributed. A centralized WAN consists of a central computer (at

a central site) to which other computers and dumb terminals connect. The Internet, on the other

hand, consists of many interconnected computers in many locations. Thus, it is a distributed WAN.

Full-Duplex vs. Half-Duplex Communications :

All network communications (including LAN and WAN communications) can be categorized as half-duplex or full-duplex. With half-duplex, communications happen in both directions, but in only one direction at a time. When two computers communicate using half-duplex, one computer sends a signal and the other receives; then, at some point, they switch sending and receiving roles. Chances are that you are familiar with half-duplex communications. If you have ever used a push-to-talk technology, such as a CB radio or walkie-talkie, you were communicating via half-duplex: One person talks, and then the other person talks. Full-duplex, on the other hand, allows communication in both directions simultaneously. Both stations can send and receive signals at the same time. Full-duplex communications are similar

to a telephone call, in which both people can talk simultaneously.

Example:

Read More

Local Area Network

Local Area Network:

By definition, a local area network (LAN) is limited to a specific area, usually an office, and cannot extend beyond the boundaries of a single building. The first LANs were limited to a range (from a central point to the most distant computer) of 185 meters (about 600 feet) and no more than 30 computers. Today’s technology allows a larger LAN, but practical administration limitations require dividing it into small, logical areas called workgroups. A workgroup is a collection of individuals (a sales department, for example) who share the same files and databases over the LAN. Figure 1.1 shows an example of a small LAN and its workgroups.

Example:

FIGURE 1 . 1 A small LAN

Read More

Network Elements

Network Elements:

In the computer world, the term network describes two or more connected computers that can share resources such as data, a printer, an Internet connection, applications, or a combination of these. In the following sections, we’ll discuss each type of network and describe the situation that is most appropriate for its use.

Read More

Network Fundamentals

Network+™  

"Quoting one of e-books"

Chapter 1 :

            Network Fundamentals :

                  Network Elements:

                        Local Area Network

                        Wide Area Network

                        Host, Workstation, andServer

                        Peer-to-Peer vs.Client/Server Architecture

                  Physical Topologies:

                        Bus Topology

                        Star Topology

                        Ring Topology

                        Mesh Topology

                        Backbones and Segments

                        Selecting the RightTopology

                    Physical Media:

                        Coaxial Cable

                        Twisted-Pair Cable

                        Fiber-Optic Cable

                        Cable Type Summary

                    Common NetworkConnectivity Devices:

                        NIC

                        Hub

                        Switch

                        Bridge

                        Router

                        Gateways

                        Other Devices

                    Summary

                    Exam Essentials

                    Review Questions

                    Answers to Review Questions 

*************

"Quoting one of e-books"

Read More

Design Hotspot-30 Server Mikrotik

Design Hotspot-30  Server Mikrotik

حمل من هنا 

رجاء تغيير بيانات الاتصال 

مع تحيات كنزى نت

Read More

 Mikrotik SSH (Secure Shell) Server and Client

Quoting one of e-books

Table of Contents

Summary

Specifications

Related Documents

Additional Documents

SSH Server

Description

Property Description

Example

SSH Client

Property Description

Example

General Information

Summary

SSH Client authenticates server and encrypts traffic between the client and server. You can use

SSH just the same way as telnet - you run the client, tell it where you want to connect to, give your

username and password, and everything is the same after that. After that you won't be able to tell

that you're using SSH. The SSH feature can be used with various SSH Telnet clients to securely

connect to and administrate the router.

The MikroTik RouterOS supports:

• SSH 1.3, 1.5, and 2.0 protocol standards

• server functions for secure administration of the router

• telnet session termination with 40 bit RSA SSH encryption is supported

• secure ftp is supported

• preshared key authentication is not supported

The MikroTik RouterOS has been tested with the following SSH telnet terminals:

• PuTTY

• Secure CRT

• OpenSSH GNU/Linux client

Specifications

Packages required: security

License required: level1

Home menu level: /system ssh

Standards and Technologies: SSH

Hardware usage: Not significant

Related Documents

• Package Management

Additional Documents

• http://www.freessh.org/

SSH Server

Home menu level: /ip service

Description

SSH Server is already up and running after MikroTik router installation. The default port of the

service is 22. You can set a different port number.

Property Description

name (name) - service name

port (integer: 1..65535) - port the service listens to

address (IP address | netmask; default: 0.0.0.0/0) - IP address from which the service is accessible

Example

Let's change the default SSH port (22) to 65 on which the SSH server listens for requests:
[admin@MikroTik] ip service> set ssh port=65
[admin@MikroTik] ip service> print
Flags: X - disabled, I - invalid
# NAME PORT ADDRESS CERTIFICATE
0 telnet 23 0.0.0.0/0
1 ftp 21 0.0.0.0/0
2 www 80 0.0.0.0/0
3 ssh 65 0.0.0.0/0
4 X www-ssl 443 0.0.0.0/0
[admin@MikroTik] ip service>

SSH Client

Command name: /system ssh

Property Description

port (integer; default: 22) - which TCP port to use for SSH connection to a remote host

user (text; default: admin) - username for the SSH login

Example

[admin@MikroTik] > /system ssh 192.168.0.1 user=pakalns port=22
admin@192.168.0.1's password:
MMM MMM KKK TTTTTTTTTTT KKK
MMMM MMMM KKK TTTTTTTTTTT KKK
MMM MMMM MMM III KKK KKK RRRRRR OOOOOO TTT III KKK KKK
MMM MM MMM III KKKKK RRR RRR OOO OOO TTT III KKKKK
MMM MMM III KKK KKK RRRRRR OOO OOO TTT III KKK KKK
MMM MMM III KKK KKK RRR RRR OOOOOO TTT III KKK KKK
MikroTik RouterOS 2.9rc7 (c) 1999-2005 http://www.mikrotik.com/
Terminal unknown detected, using single line input mode
[admin@MikroTik] >

See you in the next lesson

Mr.Mohamed samir™

Read More