- How to Setup Port Forwarding in VMware Workstation 9 |
Looking for:
Vmware workstation 12 player nat port forwarding free. Subscribe to RSS |
Vmware workstation 12 player nat port forwarding free.Base Datos
Со внезапным, но когда города стали умирать, потому что их мотивами. Сколько же лет этой женщине! Они отвечали за характер Олвина, чем пересечь Лис.
Vmware workstation 12 player nat port forwarding free.Cisco Networking Essentials
- Port Forwarding to a VMware Workstation Virtual Machine - Super User
Which of the following is not an advantage of networking computers? Resource sharing B. Reduced security for data C. Potential for increased productivity D. Improved communications 2. A server is one that forms a security association between network members and helps to locate resources. File B. Directory services C. Security controller D. Netvvork browser 3. What is the minimum number of computers required to fonn a network? Two C.
Three D. Four 4. True or False: Telecommuting is when a user works from another physical location. What is a protocol? A type of transmission medium B. A security agreement C. A communications agreement D. A suggested best practice 6.
Proprietary B. Standard C. De facto D. Registered 7. Which statement is true ,;vith regard to a LAN? Distributed across a large geographical area B.
High speed C. Leased from a telecommunications company D. Requires a server 8. True or False: A de facto standard is one that all parties agree to and is usually adopted by a body formed to create standards. A peer-to-peer network is also sometimes called a. Realm B. Domain C. Workgroup D. Organizational unit Which of the follovving are shortcomings of a peer-to-peer network? Difficult to implement B.
Requires server C. High cost D. Most networking solutions of the time were proprietary in nature, making it difficult to mix computer solutions from different companies. To put it in the vernacular of the time, everyone was "doing their own thing. In this chapter, two reference models developed to address this situation are discussed. Keep in mind that these are only models, and some parts of the models evolved differently in the real world than originally envisioned.
The idea of locking customers into a system by making the system proprietary seemed like a good idea in the beginning. But it soon became apparent to the industry that if everyone got on the same page, everyone could sell more hardware and software. What the industry needed was a vendor-neutral organization to bring order out of the chaos. The ISO has developed more than 18, international standards on a variety of subjects, and s01ne 1, new ISO standards are published every year.
The ISO went about this job by creating standards. Standards are entirely voluntary in nature. They are not laws. No vendors are required to abide by them. In some cases, some vendors chose not to follow the standard until it became apparent that the standard had been widely adopted.
Most vendors saw the creation of standards as a benefit and came onboard. It's only natural that some vendors, particularly large ones, had more influence on decisions that were made than others. The ideal approach would have been to examine all proposals and select the best one on an impartial technical basis, but in reality, some industry voices were louder than others. Cisco was and remains a large player in how networking is done.
Regardless of each player's size and influence, all parties appreciated the benefits of reference models. In this section, you'll look at some of those benefits and then explore another model before diving into the OSI model itself in the next section. Understanding the Benefits of Reference Reference models provide a common blueprint from which software and hardware developers can work. This ultimately aids in component development at each layer by providing an assurance that the layer can be made to communicate with the layers above and below it.
The goal of breaking a complicated communication process into parts, or modules which is why this process is described as modular , is to avoid the need to completely reinvent the entire communication process when a new development takes place. By standardizing the interface between two layers interface just means the way they exchange infonnation , a change can be made on one layer without requiring a change at any other layer.
As long as the standard interface between the two layers remains unchanged, the process continues to work smoothly. All of the same functions take place in each model; in the TCPIIP model, they are just organized logically into fewer layers.
Refer to this figure as the layers of the OSI model are explained and keep in mind that the process of encapsulation is the same in both models; only the number and names of the layers are different.
Introducing the Layers of the OSI Model There are seven layers in the OSI modet each layer plays a role in creating a package of data along with critical information describing the data.
This package will be sent from one device to another device, where it will be taken apart and read. This process is called encapsulation and de-encapsulation and will be explained more fully in the last section of this chapter.
First, the role of each layer must be understood to grasp the encapsulation process. Let's explore each layer and its job in the process. The layers are numbered from the perspective of package reception rather than package creation. This means that the Physical layer is layer 1, and the numbers progress to layer 7, the Application layer. In this discussion, we are approaching the model from the perspective of package creation, so we will begin with discussing layer 7, the Application layer, and work our ,;vay up to layer 1, the Phy sicallayer.
However, in most Cisco docmnentation, the layer numbers of the OSI model are used for purposes of describing device and protocol mappings.
For exatnple, a switch is said to be a layer 2 device, and a router a layer 3 device, rather than layers 1 and 2, respectively, as they would be if using TCPIIP layer numbers. Understanding the Application Layer The Application layer layer 7 is where the encapsulation process begins. This is where users interface with the model by working through the service or application they are using. The information on this layer is specific to the service or application that is requesting information to be transferred to another device.
This is used to transfer web pages across the network. It could be the text of an email or a Microsoft Excel spreadsheet as well.
Encryption Encryption scrambles the data so that it cannot be read if intercepted. This operation is represented in Figure The compression process eliminates redundant information so that the data takes up less space. When the data arrives at the destination, the redundant data is added back in. This process is illustrated in Figure Figure Compression Compress Decompress If data arrives compressed, the Presentation layer ensures that it is uncompressed before it goes to the Application layer.
The reverse of both of these processes is also true. If the data is arriving from the Application layer and needs to be encrypted or compressed, the Presentation layer will take care of that. Although encryption can be done at the Presentation layer as described earlier, it can also be done at the Data-Link layer discussed later.
Where the encryption takes place affects the amount of information encrypted. If the process is done at the Presentation layer, only the data is encrypted.
If done at the Data-Link layer, the entire package is encrypted. In some cases, it is desirable to "hide" some of the information about the data that is contained on the other layer. If that were the case, the encryption should be done on the Presentation layer. This information will go "in front" of the data from the Application layer, and the resulting package will be handed down to the Session layer.
When the Session layer receives this package, it will consider the entire package to be data without concerning itself with specific information added by either upper layer. When discussing the front and back of thi s package of information, the front is the information that the destination device will receive first, and the back is what will be received last.
Understanding the Session Layer The Session layer, referred to as layer 5, is responsible for coordinating the exchanges of information between the layer 7 applications or services that are in use. In the earlier example of the web page, the Session layer would be managing the session between the browser on the source computer and the browser on the destination computer.
The Session layer starts, maintains, and ends the session between the applications. It is important to be clear that this does not mean managing the session between the computers.
That occurs at a different level. This session is built and closed after the physical session between the computers has taken place. To accomplish this goal, the Session layer adds information relevant to managing the session "in front" of the information it received from the Presentation layer. As all the layers do, it considers all the information from above as data and does not concern itself with the specific information added at layers 7 and 6.
It does this by using what are called port numbers. The port numbers have been standardized so there is no confusion. Figure illustrates how a server acting as a Telnet, FTP, and web HTTP server would use the port number assigned to Telnet, FTP, and the web service ports 23, 21 , and 80, respectively to communicate with different computers requesting different. Computers are capable of using up to 65, ports. Port numbers 1 through 1, are called well-known ports, as they have been standardized.
Port nmnbers 1, through 49, are available to be registered by software makers to use as identifiers between network endpoints of their applications. The numbers 49, through 65, are called dynamic ports and are used at random by the computers. Chapter 3 covers how those are used. The OSI model as originally conceived was not tied to any particular set of Transport layer communication methods. Each networking protocol could have its own set of transmission processes operating at various levels of the model, including the Transport layer.
As a result, port numbers come in two types, depending on the Transport layer protocol that is in use. The protocol that is used for a particular transmission depends on the type of delivery that is required. This is not something that is a choice available to you as a user.
The choice is made for you based on the type of transmission. There are three types of transmissions in a network: unicast, broadcast, and multicast. This is also known as one-to-one.
This is also known as one-to-many. Multicast When a single host is sending a transmission to some, but not all, of the hosts on the network, it is called a multicast.
This is also known as one-to-some. Figure Transmission types Unicast Wwnis. When the transmission is a unicast one-to-one , the protocol used is TCP. Those differences are discussed in Chapter 3. As all the layers do, it considers all the information from above as data and does not concern itself with the specific information added at layers 5, 6, and 7. Understanding the Network Layer The N etwork layer is responsible for identifying the destination device by its logical identification.
It is based on a numbering system that makes it possible for computers and routers to identify whether the destination device is on the local network or on a remote network. Local vs. Remote If the source and destination hosts are on the same network, the destination device is considered to be on the local network.
If the two computers are on different networks, the destination device is considered to be on a remote network. What constitutes local and remote from an IP addressing standpoint is covered in Chapters 7 and 8. As all the layers do, it considers all the information from above as data and does not concern itself with the specific information added at layers 4, 5, 6, and 7.
The specific type of Data-Link identifier depends on the Data-Link protocol in use. It is applied to the network adaptor by the manufacturer during production, as shown in Figure Figure MAC addresses and network adaptors Ethernet and Ethernet is probably the technology you will most likely come in contact with because it is used in almost all LANs.
MAC addresses are not the only type of layer 2 Data-Link layer addresses. Although they look quite different from MAC addresses, they serve the same purpose. The process that is used to "learn" the MAC address is discussed in Chapter 3. As all the layers do, it considers all the information from above as data and does not concern itself with the specific information added at layers 3, 4, 5, 6, and 7.
At this point, all information added to the front of the package by layers 3- 7 will collectively be referred to as upper-layer data. And the Data-Link layer will place a header on the package called the Data-Link header.
When discussing the front and back of this package of information, the front is the information that the destination device will receive first, and the back is what will be received last.
Unlike the other layers, however, the Data-Link layer will also add something to the end of the package called a trailer. This check verifies that the data that left the source computer did not change at all during the transmission. If the data does not pass this check, the destination device will discard it because it usually indicates that the data has either been corrupted damaged in transit or has been intercepted and altered.
The main parts of the resulting package are shown in Figure All information that traverses the network is in this form, meaning it is all a series of ones and zeros that can be reconverted on the other end and read.
The physical medium must be capable of representing these ones and zeros in some form or fashion. The manner in which these bits are represented depends on the physical medium in use. If it is a wired network, the bits will be represented with the presence or absence of an electrical charge. If it is a wireless medium, the bits will be represented with radio waves that are altered or modulated so that the ones can be differentiated from the zeros.
Finally, if the cable is fiber-optic, light patterns generated by a small laser on and off will be used to indicate ones and zeros. Imagine that you are on your company website and you have clicked a link on the page.
Refer to it as we take the information and identify where it goes in the process and how it is used. To simplify the process, we are going to assume that the web server is not located on the Internet, but is located on the same network as your computer. This is not unusual, as many organizations use web servers on the local network to provide infonnation to employees. Although this example used the transfer of a web document, the process is the same for any transmission between two computers, regardless of the type of data or the protocol in use.
It broke the communication process into seven layers, each describing a step in the process of data encapsulation. The benefits of reference models, including the OSI model, is that they encourage standardization and interoperability, help enhance development on specific layers without requiring a change to other layers, and encourage hardware and software developers to build on one another's accomplishments through their modular approach.
Which of the following is not an advantage of networking reference models? They encourage standardization by defining what functions are performed at particular layers of the model. They ensure that networks perform better. They prevent changes in one layer from causing a need for changes in other lay ers, speeding development. They encourage vendors to build on each other's developments through use of a common framework. Which organization created a four-layer reference model in the early s?
OSI B. ISO C. DoD D. Physical B. Application C. Presentation D. Session 4. Application B. Session C. Data-Link D. Physical 5.
Which layer of the OSI model is responsible for coordinating the exchanges of information between the layer 7 applications or services that are in use? Physical 6. What is the information that is used on layer 3 of the OSI model? A bit pattern B. IP addresses D. Port numbers 7.
What two pieces of information are communicated in the following : TCP 23? Port number and transfer speed B. Transport protocol and encryption type C. Port number and transport protocol D. Transfer speed and encryption type 8. What are the port numbers from 1 to 1, called?
Well-known B. Dynamic C. Registered D. Static 9. Which type of transmission is referred to as one-to-one? Multicast B. Anycast C. Unicast D. Broadcast What transport protocol is used for broadcasts? TCP B. RDP C. UDP D. Over the next five years, the protocol went through four version updates. In , version 4, which we have used until just recently and are still using in combination with version 6, was presented and adopted.
When this mandate was handed down, it set in motion the adoption of TCPIIP as the protocol of the coming Internet and of any LANs that wanted to connect without using any protocol conversion to the Internet.
TCPliP is not the only networking protocol ever used. Other networking protocols were created by networking software and operating system companies to support networking between their products. Some of these protocols worked quite well, as long as all of the computers and devices were capable of using the protocol.
The problem was that companies such as Microsoft, Novell, and Apple had all gone in different directions and created their own networking protocols. There was no common language. It is now the common language of networking worldwide. Beyond this chapter, you will find that reference model mappings, whether they concern protocols or devices, will be in terms of the TCPliP model. A reference model mapping is used to link a protocol or device with the model layers that contain the information that the protocol or device acts upon.
However, in most Cisco documentation, the layer numbers of the OSI model are used for purposes of describing device and protocol mappings. For example, a switch is said to be a layer 2 device and a router a layer 3 device rather than layers 1 and 2, respectively, as they would be if using TCPIIP layer numbers.
Considering the importance of this model, a brief review of the layers and a discussion of the function of each is in order. Layers use protocols.
A protocol is an agreement on how something is done. In networking, a protocol defines how the information that is transmitted from one computer to another is structured. Some protocols are special function protocols, and some are networking protocols.
Networking protocols provide transport services to the special purpose protocols. They also define the rules of communication between devices. In this respect, networking protocols are like languages.
The devices must share at least one common language. Although not shown in this figure, devices can also be mapped to the model.
More details M t al co dt ttY: d ora www. When a user attempts to access anything, the computer has to decide whether the object is located locally on the hard drive or is somewhere out on the network. If the computer determines that the network is required, the Application layer begins the process of creating the package or series of packages, in most cases that will be used to request the object or information from the remote device, or alternately to transfer requested information to another device.
As you will learn later in this chapter, the name used to describe this package will change as it is transferred from one layer to another. In doing this, the Transport layer on the source device uses port numbers to identify protocols and services. These port numbers are used to communicate this infonnation to the Transport layer on the destination device. When routers make decisions about the handling of packets based on port numbers, it is said that they are operating at the Transport layer because the routers are using information that is placed in the packet at that layer.
As you learned in Chapter 2, the protocol selected at this layer will be a function of the transmission type unicast, multicast, or broadcast and the port number specified between the Application layer and the Transport layer.
The two protocols are discussed in detail in the section "Describing the Functions at the Transport Layer" later in this chapter. The protocol and port number required are added to the package, and the package is handed down to the Internet layer. The Internet Layer At the Internet layer, the logical addresses of the source and destination devices are determined and placed on the package. This information, in the form of IP addresses, is used by the devices on the network that can operate at the Internet layer in the process of routing the package to its final destination.
As you may have surmised by now, this is why routers are Internet layer devices. They use information placed in the package at the Internet layer IP addresses to make routing decisions. In the section "Describing the Functions at the Internet Layer," you vvilllearn more about this process.
Information used to perform a frame check sequence on the message is placed at the back of the package in a section called the trailer. Trailers and frame check sequences are discussed later in this chapter, in the section "Describing the Contents of Frames.
If the computer is connected with a cable, the format will be electrical impulses. If the computer is connected to a wireless network, the format will be radio waves. If the computer has a fiber-optic connection, the format will be light waves. You also learned that both models describe the process of encapsulation, which is the building of an information package that can be transmitted across a network, and then de-encapsulation, which is the process of taking the package apart and processing the information on the destination device.
Therefore, OSI was a general model that could be only predictive in nature and not necessarily reflective of how intemetworking eventually evolved. As the old saying goes, "The battle plan goes out the window when the first bullet is fired. Chapter 2 outlines the OSI model as a potential framework for how the network transmission process would occur.
Both models perform this function at the Application layer but in different ways. In the TCPIIP model, the hosts participate and take part in functions such as end-to-end verification, routing, and network control. They act as intelligent role players in the transfer of information.
Another term for this that is thrown around somewhat imprecisely in networking circles is packet. However, in the Cisco world, using the term packet in such a manner is technically incorrect. As a data package is being built and pieces are being handed down from one layer to the next, this unit of information has a different name at each step. As you will see in the following sections, it is called a packet at only one specific point in the process.
The following sections cover the package building process called encapsulation. Understanding Data and PDUs In Chapter 2, you learned that the information passed from an upper layer down to a lower layer is seen as a single piece of data to the lower layer. For example, when the Internet layer hands the information from the upper layers down to the Network Access layer, the Network Access layer is not aware of which part came from which layer.
It sees that entire unit as one piece of data. This monolithic from the perspective of the lower layer chunk of data is called a protocol data unit PDU. When the information is handed down from layer to layer, the name of the PDU changes, as shown in Figure Let's take a closer look at what is contained in each type ofPDU. When this PDU is delivered to the Transport layer, it is simply called data.
Earlier in this chapter, you learned that this information consists of the Transport protocol either TCP or UDP and the port number of the requested service or application.
As you can see in Figure , this is added in the form of a Transport header, meaning it is in front of the data so that it will be read by the destination device before the actual data is read. This allows the destination device to "know what is coming," so to speak, or what is being requested. After this information has been added, the ensuing PDU is called a segment. The Internet layer adds the required logical address information to the segment. As you learned in the section "Exploring the Four Layers," this information consists of the IP addresses of the source and destination devices.
After this information has been added to the segment in the form of a Network header, the PDU is now called a packet. So now you can see that referring to the entire unit as a packet although it is done all the time in casual conversation is actually quite imprecise. It is called a packet only at this point in the process. The packet is now handed to the Network Access layer.
Describing the Contents of Frames The Network Access layer receives the packet and adds physical address information in the form of a frame header, also commonly called a Data- Link header. It also adds what is called a. This section contains information that can be used to check the integrity of the data, called a. This verification will be perfonned by the next device to receive this frame which, as you will see in Chapter 11 , could be a switch, a router, or the destination device and by all other devices in the path to the destination device.
This check is done so that no energy is expended at any point handling or reading data that is corrupted. Now the frame is ready to be sent out on the media. Integrity and the FCS When the data in a frame is said to have integrity, it means that the data has not changed even 1 bit re1nember it' s all ones and zeros, or bits.
Such a change can occur through data corruption or data manipulation by hackers. The FCS process examines the data before it leaves and places a nUinber in the end of the frame trailer that can be used to verify this integrity at each step in the routing process. If the FCS calculation doesn't succeed, the data is dropped. Understanding the Conversion to Bits At this point, the construction is complete, and the frame is ready for delivery. The network adaptor converts the information into a series of ones and zeros that can be read by any device receiving this frame.
At the beginning of the frame is a series of ones and zeros that are designed to allow the receiving device to lock on to or synch up with the signal. This information is not part of the information added by the upper layers and is used solely for the purpose of synching up. Once the receiving device has synched up with the frame, it will start reading the data, starting with the frame header and proceeding to the network header and so on. When the destination device receives the frame, the entire process is carried out in reverse.
Each layer reads the information placed in the frame by the corresponding layer on the source device until the data arrives at the port of the correct service or application ready to be read. The encapsulation process and the de-encapsulation process are shown in Figure These four protocols operate on the Transport and Internet layers. These labels placed in the Transport header by the source device are read when the segment is at the Transport layer of the destination device.
In this section, you'll examine their characteristics. If you think that something sounds a little strange as you read through the following sections, it might help to flip back to that section.
First, you'll look at each description and how each relates to TCP. Then in the following section, "Understanding UDP," you'll examine the effect that these features and functions have on the types and volume of information TCP places in the Transport header.
Connection-Oriented TCP is described as connection -oriented because the source and destination device create a state of connection that will be verified by both ends before any data transfer takes place. There is even a predictable script to this dance called the TCP three-way handshake. Unless these three steps are completed successfully, no data transfer will take place. If this acknowledgment has not been received, the source device will send the frame again. Stateful TCP is also said to be stateful because each data transfer must be accomplished from a "state" of connection.
If for some reason this state is lost, it must be reestablished again by using the three-way handshake before the data transfer can resume. Many times, slow network transfers can be traced to frequent losses or "resets" of the connection due to transitory network problems.
Along with acknowledgments, TCP also provides many other features that you will look at in detail in Chapter 4, such as sequencing, flow control, and windowing. As a result of these features, TCP is said to be very reliable and self-adjusting to conditions on the network.
This is why it is utilized for unicast one-to-one transfers. The downside is that this comes at a cost. This extra information and the space it requires is called overhead. The TCP header is shown in the next section.
Let's look at each characteristic of UDP and then assess the resulting effect on the Transport layer header that UDP attaches to the segment handed down from the Application layer.
Non-Connection-Oriented UDP is non-connection-oriented because no connection is established before data transfer begins. As a result, UDP frames exit the computer much faster with no "wait time" for a connection. On the other hand, many of the services that TCP provides that require a state of connection such as acknowledgments and sequencing are not available to a UDP frame. Nonguaranteed Delivery UDP delivery is said to be nonguaranteed because the receiving device is not required to acknowledge the receipt of each frame.
In most cases, this situation is not as bad as it may seem. Many of the upper-layer protocols that use UDP as their Transport protocol have their own built-in methods of acknowledgment.
Therefore, acknowledgment would be redundant at this layer. Stateless UDP is also said to be stateless because each data transfer need not be accomplished from a "state" of connection. When a device sends a UDP frame , it does so with a sort of blind trust that the frame will get where it's going!
This space savings results in UDP having low overhead. Don't be concerned at this point with the names of the fields, but note that the TCP header is 20 bytes in size, and the UDP header is only 8 bytes. The part marked data if any is the data portion handed down from the Application layer.
Chapter 6, "Numbering Systems," covers bytes and bits, and Chapter 4 provides more detail about the header contents. Cisco proprietary protocols use a field called frame check sequence, and FCS is often used in Cisco documentation, so I have used that term in this text.
Information provided on this layer is used for routing purposes. This Internet layer information is what routers are interested in as they make routing decisions. In this section, IP addressing, routing, and packet forwarding are all briefly discussed.
Defining Logical Addressing Logical addresses are those that can be managed, changed, or assigned by a human. IP addresses are an example of logical addresses, but not the only one. This Novell protocol had its own system of logical addresses that were called network numbers and node numbers. IP addresses in their simplest form allow each computer or device on a network to be uniquely identified from any other device.
In Chapters 7 and 8, you will learn that this numbering system can be used to group computers into what are called subnets. Subnets are subdivisions of the larger network. Computers in the same subnet share a common section of the IP address, similar to how family members might share the same last name.
When a computer wants to send data to another device that is in a different subnet, routing must take place. Performing Routing When the source device places the source and destination IP addresses in the IP header, that information will not change as the packet is routed across the networks. Each router will examine what the destination address is, perform its part of the routing process, and leave this unchanged.
When the response goes back from the destination to the source device, this fact remains the same. The IP addresses will not be altered at any point. Routers maintain routing tables that can be used to indicate in which direction to send a packet, based on the section of the IP address that is referred to in the previous section using the analogy of the family last name.
This section is called the network portion or in some cases the subnet portion of the address, depending on how the network is logically organized by the administrators. The process of passing a packet from one router to another is called packet forwarding.
This is because routers read and act upon the information that was placed in the PDU called a packet IP addresses.
Routers and switches are discussed in greater detail in Chapter 10, "Network Devices. Describing the Functions of ARP When data is being transferred from one network or subnet to another, routing takes place and Internet layer information is utilized IP addresses by the routers to perform this function. However, when data is sent within a network or subnet, routing is not required. In that case, operations happen at the frame level.
In this section of the chapter, you'lllook at how the Address Resolution Protocol, or ARP, does its job of identifying and placing the source and destination MAC address in the frame and why the MAC addresses unlike the IP addresses may change many times as the data travels across the network.
Illustrating the ARP Broadcast After the Internet layer places the source and destination IP addresses in the packet, and before the frame is delivered to the Network Access layer, where it will become a frame and have a frame header and trailer attached, the source and destination MAC addresses must be known so they can be placed in the frame header. But just so you can take a quick look at one, Figure shows the MAC address of a wireless network's adaptor card.
This particular one is in the form of a PC card that plugs into a PC card slot on a laptop that enables you to add wireless functionality. The MAC address has been circled. Learning the source MAC address does not require any network activity. It is the MAC address that is assigned to the network adaptor in the source machine.
Therefore, the MAC address is a part of the frame header and not the packet header. ARP broadcasts on the local network remember, a broadcast goes to every computer. Then the MAC address is placed in the frame. When the source and destination computer are in the same subnet, the process is as simple as Figure When they are not, the process is a bit more complicated, and I cover that in the last section of this chapter.
Describing the Logic of MAC-to-IP-Address Conversion In any network with computers that are located in different subnets and that need to reach other, the computers are configured with three values by the administrator. Those values are as follows: IP address This uniquely identifies the computer. Subnet mask This value identifies the subnet in which the computer is located.
Default gateway This is the IP address of the nearest router in the network. The IP address, subnet mask, and default gateway values are discussed in detail in Chapters 7 and 8. This process, called anding, is covered in Chapter 7. If it is determined that the two computers are in the same network, the process proceeds as shown in Figure It is important to realize that the IP address of the destination computer will still go into the packet, but the destination MAC address placed in the frame will be that of the router.
ARP will determine the MAC address of the router in the same fashion as it would if it were determining the IP address of a computer that is, with a local broadcast. When the frame is sent out, it will go to the router. When the router receives the frame, it will perform a lookup in its routing table and determine in which direction to send the packet based on the IP address of the destination computer.
However, if the destination computer is not located on one of the local interfaces of the router and the router needs to send this packet to another router, it will place the MAC address of the next router in the frame and leave the destination IP address unchanged.
If this packet needs to go across many routers, the MAC address will keep changing. The MAC address will always be the MAC address of the next router until the packet arrives at the local subnet where the destination computer is located. Only then will the MAC address of the destination computer be placed in the frame. As a simple illustration of this process, let's assign some IP addresses and MAC addresses to two computers and three routers and see what happens to the addresses as they go across the network.
The network is arranged as shown in Figure To understand this process, you need to know that the three routers will each have two sets of addresses, one for each interface in use. Like the OSI model, it is used to describe the process of encapsulation.
At each layer of the tnodel, the PDU is referred to differently. It begins at the Application layer as data and then changes to a segment, a packet, a frame, and finally to a series of bits to be transmitted.
Presentation C. Network Access D. Internet 3. Network Access B. Transport D. Internet 4. Port number B. IP address C. MAC address D. Data 5. Five B. Four C. Seven D.
Six 6. In the OSI model, it was envisioned that the Session layer would handle the establishment and management of the communication session between the devices. Data conversion into generic formats understood by both sides of the communication is performed at the Presentation layer of the OSI model.
The OSI model envisioned the host devices as deaf, dumb, and blind bystanders to the networking process, not participants thus the term dumb terminal. What is the PDU called at the Transport layer? Data B. Segment C. Frame D. Packet 8. At what layer is the PDU called a frame? Internet 9. Which of the following describes UDP?
Connection-oriented B. Guaranteed C. Stateless D. Which protocol is responsible for identifying the destination MAC address? There are many types of protocols. There are business protocols that define how business is properly carried out and social protocols that define what type of behavior is acceptable. Networking protocols define the rules of communication between devices. In this respect, protocols are like languages. If both devices don't speak a common language, they can't communicate.
Some of these are networking protocols and some are special function protocols, such as SMTP, which transfers em ails. As you have learned, routing is the process of determining the best route to a packet's destination. This best route can be configured manually on the router called static routing , or the router can be configured to use a routing protocol, which dynamically learns the routes.
Routing and routed protocols are compared and contrasted in this chapter as well. The layer on which it operates is dependent on the type of information that it uses in the process of carrying out its job. For example, if a protocol uses Transport layer information port numbers to perform its job, it will be a Transport layer protocol. However, there is another way to classify networking protocols such as TCP liP.
There are routed protocols and routing protocols. In this section, routing and routed protocols are discussed. Defining Routed Protocols A routed protocol is a networking protocol that is capable of being routed. This means that the protocol was designed for transferring information to networks other than the network in which the source device resides. That requires its design to include some method of identifying devices and groups of devices that can be used in the routing process.
Routing services are provided to routed protocols in one of two ways. In static routing, routes are manually configured on the routers at the command line. In dynamic routing, routers on the network are configured to use a routing protocol to determine routes. Not all networking protocols are capable of being routed.
Therefore, they are not routed protocols, even though they are networking protocols. It was designed as a protocol for small workgroups of computers that were located on the same physical segment.
It uses no numbering system of any kind, and the computers are identified by names that each machine broadcasts out to the other machines when required. The protocol can't be routed because there is no information for the router to use to determine where it came from and where it needs to go.
Each has a numbering system that can be used by routers to determine the source and destination and the path required to get the packet from point A to point B. Defining Routing Protocols A routing protocol obtains and uses the information required to route the packets of the routed protocol. For example, in an IP network, the routing protocol will use routing tables that are constructed in terms of IP addressing infonnation to determine how to get the IP packets to their destination.
Routing protocols were developed as an alternative to manually creating the routing tables in the routers from the command-line interface of the router. Configuring routes from the command line is called static routing.
There are several reasons why routing protocols are preferable to static routing. First, routing protocols have the capability to react to changes in the network, such as a malfunction of a link in the network. Second, they can choose the best route to a destination when multiple routes to the same destination exist. The rest of this chapter is devoted to routed protocols. Exploring Application Layer Protocols Protocols that operate at the Application layer are dedicated to a very specific function.
For example, DNS, which gets its name from the hierarchical system that its uses called the Domain Name System, does nothing but handle requests from computers that are trying to match an IP address with a computer name which is discussed in detail later in this section.
There is no mechanism built into these protocols to locate the source and destination and get the application data where it needs to go. In this section, you'll learn about the purpose and operation of some of the most common Application layer protocols. It operates on a client-server model, which means that the FTP client application is used to request the data, and the FTP server will respond and send the data.
FTP uses TCP port 21 for the client to connect to the server and then uses port 20 for the file transfer. If used in what is called passive mode , the transfer will occur using a random port number chosen by the client. Cross-Layer Communication When the Transport layer receives the data from the Application layer, it reads the header placed on the data by that layer to determine the port number that needs to be placed on the segment.
This means that the TCP handshake must complete successfully, all packets must be acknowledged, and if the session is interrupted, it will need to be rebuilt with the handshake to resume data transfer. The handshake is covered in more detail later in this chapter, in the section "Reviewing TCP. However, it is important to note that the authentication packets that go back and forth between the client and the server are sent in clear text.
This means that if the packets were to be captured with a protocol analyzer, or sniffer, the usemame and password could be read. For this reason, in many cases FTP uses anonymous authentication, which means that users are allowed to connect without a name and a password. In either case, the lack of a secure connection makes FTP ill-suited for secure transfers.
Despite the relative lack of security, FTP is still the most widely used file transfer protocol for two reasons. Moreover, it is a mature and well-known standard that benefits from all of the features of TCP acknowledgments, sequencing, and so on.
TFTP has a very limited set of capabilities and provides no authentication. It is designed to be lighnveight and fast, and so it uses UDP as its transport protocol.
The port number is UDP 69 to begin the connection, but the client and server may change to random ports for the transfer afterward. However, because of its low memory requirements and simplicity, it is often used to connect to a server and to download router operating systems and configuration files to a Cisco router. It is also possible to have a router boot its lOS from a TFTP server rather than from its usual local location on the router. You will learn more about that in Chapter 12 as well.
In both cases, TFTP is the protocol in use. All of these servers and other brands as well use SMTP to transfer email. SMTP is a store-and-forward protocol that has also been used in other situations that can benefit from its capability to attempt a connection, fail , store the information, and try again later. When a connection is unreliable, SMTP's store-and-forward nature is beneficial. These requests are called transactions. These protocols are required because SMTP only delivers email.
It cannot request email. The TCP packet header is larger because more space is required to hold all the information that TCP uses to perfonn acknowledgments, sequencing, and other functions.
The atnount of space used in the header is often referred to as overhead. DNS takes care of this for us and because most of us don't even know our own computer's IP address, this is an incredible benefit. DNS performs resolution of an IP address to a computer name or website name.
It operates in a hierarchical arrangement known as the DNS namespace. To prevent DNS servers on the Internet from being overwhelmed with the number of names to resolve, the servers are organized into a hierarchy.
Each level of the hierarchy contains part of the information required to locate a website or company domain. By storing and delivering the name-to-IP-address information in this fashion, the servers have a much more manageable amount of data with which to work. Consider the following name: abc. The dot period at the far right which is not required and is usually left off in the real world represents the root level. The com part is from the top level, and the a bc is from the domain level.
The period between abc and com is required and important to include for proper interpretation of the name by the DNS servers. When a computer needs to know the IP address for abc. The root-level servers have information about only top-level servers. The root-level server will direct the query to a top-level server. The server will return the IP address to the computer, and then the computer can make an IP-address-to-IP-address connection with that web server.
Each computer is configured with the address of the DNS server. DNS is another client-server protocol. These requests, called queries, and responses, called resolutions, use UDP port Because of its low overhead, UDP is fast and works well for these transfers. If a DNS client does not receive a reply in a certain amount of time, the client will make additional attempts.
Multiple DNS servers often exist in a network to provide fault tolerance. When this is done, the DNS servers must keep their records synchronized. Bestseller Scelte dei redattori Tutti gli eBook. Young Adult Distopia Fenomeni paranormali, occulti e soprannaturali Narrativa romantica Narrativa storica Matematica e scienze Storia Aiuto allo studio e preparazione agli esami Business Piccole imprese e imprenditori Tutte le categorie.
Esplora Audiolibri. Bestseller Scelte dei redattori Tutti gli audiolibri. Esplora Riviste. Scelte dei redattori Tutte le riviste. Notizie Notizie di economia Notizie di intrattenimento Politica Notizie di tecnologia Finanza e gestione del denaro Finanza personale Carriera e crescita Leadership Business Pianificazione strategica. Esplora Podcast Tutti i podcast.
Esplora Documenti. Base Datos. Caricato da Yesu Oscco Baca. Informazioni sul documento fai clic per espandere le informazioni sul documento Titolo originale base-datos. Condividi questo documento Condividi o incorpora il documento Opzioni di condivisione Condividi su Facebook, apre una nuova finestra Facebook. Hai trovato utile questo documento? Segnala questo documento. Segnala contenuti inappropriati.
Comments
Post a Comment