"Communication" of computers among themselves includes many devices, and one of them is a gateway. What is this? What types exist? What is their principle of operation?
What is a gateway
This is the name of a hardware router, as well as software that is used to connect computer networks. A prerequisite is the ability to use different types of protocols (for example, local or global). The gateway mask is used for recognition. This is a kind of identifier in the global network. It is considered that the gateway is installed if there is a transfer of data that is useful from the user's point of view.
What is it
The gateway converts protocols from one type to another. A good example is when the local computer and the World Wide Web are connected. Then the network gateway is used. To provide a hardware example, I suggest looking at something else. A router (router), a very popular and used device, is the same hardware network gateway. They can work with all popular operating systems. The main task performed by the network gateway is the conversion of protocols between different networks. He can acceptprocess and send packets. Moreover, data transfer can be performed both on one protocol and on several.
Gateways are such subjects of technical systems that can be implemented as a hardware or software solution, or connected together (which is the most common). But usually they mean applications installed on the router and / or computer. Gateways are devices that must understand all protocols with transmitted data. They must be able to encrypt and decode all information received and sent. Speaking about the disadvantages of gateways, it should be noted that they usually work much slower than conventional routers, switches and network bridges. They can act as a node or endpoint of the Internet. Speaking of the latter, it is necessary to distinguish between hosts and gateways. It is very important. So, the former provide web pages to computer users, and the latter connect different networks. The latter include a server that controls traffic when exchanging data between company computers and the Internet. For large volumes, the gateway is usually integrated with a firewall and proxy point. To manage the distribution and conversion of packets, it is combined with a router. Speaking of software, it can be installed both on a server and on a computer.
Gateway functions
It establishes the routes for transmitting data packets over various heterogeneous network interfaces. It can also localize all processed traffic. May be a subnet gateway, or a data link. There is also morea specific function that is not yet widely used. Now let's talk about the voice gateway. It is necessary to transmit audio traffic. The voice gateway is used in phones.
Working principle
How is it going? Gateways are devices that can run on all popular operating systems. Let's look at the data path from the moment when the user clicked on the "Submit" button. First, an explanation is carried out using machine languages, which requires a computer. Then all information is encoded in binary code. It is broken down into data packets. Each of them contains information about what it is a part of and where it needs to be. Encryption is in progress. The route is then determined and the data packets are sent to the destination. When they arrive at their destination, then the above processes occur in reverse order, with the exception that decryption is carried out. That is, this device works as a gateway router. Now let's look at what types of gateways exist.
Default gateway
In protocols, this is the address where all traffic that cannot be routed is sent. For this property, it is also called the gateway of last resort. To determine where to send data, a special routing table is used. If it is not possible to determine the ultimate goal, then they are transferred to it. I found the use of gateways of last resort in networks where the centralrouters, in their client segments, as well as just small in size. In the table, it is defined by the following entry: "network 0.0.0.0 with mask 0.0.0.0". Setting up the gateway for this is not a difficult task (usually it is configured when installing the drivers).
Call gateway
Looking ahead, I will inform you that it is not used in IDT. A characteristic feature of this gateway is that it has a WC field. Therefore, it is possible to pass 25=32 words at once to the procedure that is called via the stack.
Task Gateway
Its important advantage is its versatility - it can work in all three descriptor tables. But there are no offset fields used here, so they can take on any value. Also, as a segment, TSS has found application here. Setting up a gateway, despite its versatility, is not the easiest thing to do.
Interrupt Gateway
Used exclusively in IDT. It can reset the IF interrupt flag when it enters a processing routine. Since the previous value of the register is always stored on the stack, when the task being executed exits, it returns to its original position. An important advantage is that this gateway can handle some of the interrupts that occur in CLI mode.
Trap Gateway
It is also used exclusively in IDT. At the same time, he was awarded the title of the simplest gateway. So, when interrupts arrive, it goes to the processing procedure. If necessary, it can even be switchedstack. Let's take a closer look at one of the samples presented in the article.
Additional options for using default gateways
In general, what are they and what role do they play in data transmission? Only one possibility was outlined above, but it does not give a complete idea of what and how. So, the default gateway allows you to simplify the coordination of traffic. How? To do this, it sends all the received data to the central routers, which can see a more “voluminous” picture, and, accordingly, they have a greater chance of finding the recipient. You also need to consider what the workstation's routing table is made up of. So, it has loops, a local network segment, and the default gateway itself. The role of the latter is to receive all the traffic that the first two recipients have not de alt with. When multiple instruments or pieces of equipment are connected to the same router, using the default gateway is the only form of data addressing available. When multiple connections are used, this form of data exchange loses its value. In this case, it is not necessary to configure the default gateway.
Why does it have that name
How did it happen? It should be noted that the application varies depending on the field, although there is no difference in functionality. The term "default gateway" is used at workstations. Its use in these cases is the standard mode of operation of this piece of equipment. The term "gateway of last resort" is applied to routers where the occurrencethis situation is not considered normal, since this device must always know where to deliver information packets.
Conclusion
Summarizing, we can say that the topic of gateways is extremely capacious. If you undertake to describe in detail what and how in relation to them, then even the smallest text will exceed this article in size. But such a detailed level of presentation is still not needed by ordinary users and even those who configure them. This information may be needed only if a person himself wants to develop such a device, but here it is already necessary to write the material for a whole book.
