The two interconnection devices par excellence are routers and switches. It is important to clearly differentiate the interconnection function in each one of them.
§ The switches transfer data between devices located within the same network . § Routers transfer data between devices that are located in different networks, that is, transfer data between different logical networks. From a theoretical point of view, these functions are not interchangeable, that is, a switch can never communicate equipment located in different networks and a router can never communicate equipment within the same network. However, in practice there are exceptions ... "Hybrid" devices Indeed, the above statement is true only in the theory of networks, since in practice there are switches with routing functions, called level 3 switches , and there are routers that include several Ethernet ports together making the functions of a switch, for example the residential routers usually include 4 Ethernet ports, ie a 4 - port switch. Other functions of the routers Routers, in addition to their function as routers of network traffic, can provide many other functionalities. Here we will briefly describe some of them: § Adaptation of the data between different transmission technologies . The most typical case is the residential routers that connect residential networks with the networks of telecommunications operators to provide Internet connection services. These routers are able to exchange data between the residential user's network that uses typical local network technologies (Ethernet and Wi-Fi) and the operator's access network, which will use last-mile technologies such as ADSL, cable (HFC) or fiber. Optical (FTTH). § Provide the network configuration parameters . This function is carried out by means of a service called DHCP and it greatly simplifies the connection of a device to the network since all the network parameters are configured automatically. This function has gained special importance in residential networks, especially with the tendency to use wireless devices. § Data filtering . Data filtering is carried out mainly for security reasons. Broadly speaking, this process consists of establishing criteria under which the data can pass or not from one network to another. This filtering function is carried out by means of an element known as a firewall . § Translation of network addresses . Currently, due to the scarcity of IP addresses, practically all networks use a network address translation mechanism known as NAT that allows the use of private addresses in networks connected to the Internet. This function is implemented in many cases by routers, especially in residential routers. § Other features that can be implemented in the router currently: § Wireless access point (Wi-Fi) § Port redirection § Proxy server § Load / traffic balancing § Management of VPN connections Routers and the Internet As we have already said, when we talk about a router everyone has in mind the router that we have at home and that provides us with Internet access, however, from the point of view of interconnection, this type of router is the simplest since they only have to join two networks, the home network with the operator's network.Enterprise router is a basic product for any business/enterprise However, when we enter companies and organizations with large communications infrastructures, the picture is quite different since it increases exponentially both the traffic that is exchanged and the number of networks that must be interconnected. The same goes for the companies that provide connectivity, that is, the ISPs, operators and large Carriers. Their networks are enormously complex and require that the exchange of data between networks be fast, efficient, with a high level of availability and flexibility. Well, in these cases, routers must be fast, efficient and intelligent devices. In these cases, the function of "routing" the data becomes the highest priority. Internet itself is considered a large network of networks, that is, a large network formed by the interconnection of millions of networks. Routers have a fundamental function in this interconnection function. In fact, without the efficiency and performance of the current routers used in Internet backbones (known as core routers ), the Internet itself would not be possible as we know it.
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