Router
A router, router (from English router), or router > is a device that allows interconnecting networks with different prefixes in their IP address. Its function is to establish the best route for each data packet to reach the network and the destination device. It is widely used to connect to the Internet since it connects the network of our home, office or any network to the network of our provider of this service. Most of the routers that are used for home and offices have other additional functions incorporated into the router, such as: wireless access point, which allows you to create and connect to a Wi-Fi network; modem, which converts analog signals to digital and vice versa; Switch, which connects various devices via cable, creating a local network.
History
The first device or hardware that had fundamentally the same functionality as what we understand today as a router, was the Interface Message Processor or IMP. IMPs were the devices that made up the ARPANET, the first packet-switched network. The idea for a router (called a gateway at the time) initially came from an international group of computer networking researchers called the International Network Working Group (INWG). Created in 1972 as an informal group to consider technical issues involving the interconnection of different networks, it became a subcommittee of the International Federation for Information Processing that same year.
These devices differed from previously existing packet switches in two ways. On the one hand, they connected different types of networks, while on the other hand, they were connectionless devices, which did not ensure reliability in data delivery, leaving this role entirely to the hosts. This last idea had already been raised in the CYCLADES network.
The idea was further investigated, with the intent of creating a prototype system as part of two programs. One was the one promoted by DARPA, a program that created the TCP/IP architecture in use today, and the other was a program at Xerox PARC to explore new networking technologies, which produced the system called PARC Universal Packet. Due to the intellectual property that concerned the project, it received little attention outside of Xerox for many years.
Some time after 1974, Xerox got the first working router, although the first true IP router was developed by Virginia Stazisar at BBN, as part of that DARPA-sponsored effort, during 1975- 76. In late 1976, three PDP-11-based routers entered service on the experimental prototype of the Internet.
The first multi-protocol router was developed simultaneously by a group of researchers from MIT and Stanford in 1981. The Stanford router is credited to William Yeager and the MIT router to Noel Chiappa. Both were based on the PDP-11. Since virtually all networking now uses IP at the network layer, multi-protocol routers are largely obsolete, even though they were important in the early stages of the growth of computer networks, when various protocols other than TCP/ IPs were in widespread use. Routers that handle IPv4 and IPv6 are multiprotocol, but in a much less variable sense than a router that handled AppleTalk, DECnet, IP, and XeroX protocols. From the mid-1970s and into the 1980s, general-purpose minicomputers served as routers.
Today, high-speed routers are highly specialized, as specific hardware is used to speed up more specific routing functions, such as packet routing, and special functions such as IPsec encryption.
Operation
The basic operation of a router or router, as can be deduced from its name, consists of sending network packets along the most appropriate path or path at all times. To do this, it stores the packets received and processes the origin and destination information they contain. Based on this information, it forwards the packets to another router or to the final host, in an activity called 'routing'. Each router is responsible for deciding the next hop based on its forwarding table or routing table, which is generated by protocols that decide which is the most appropriate or shortest path, such as protocols based on Dijkstra's algorithm.
Because they are the elements that make up the network layer, they have to be in charge of fulfilling the two main tasks assigned to it:
- Packages forward: when a package arrives at the entry link of a router, it has to pass the package to the appropriate exit link. An important feature of the routers is that they do not spread diffusive traffic.
- Package wrapping: by using laminating algorithms you have to be able to determine the path that packages should follow as they flow from a transmitter to a receiver.
Therefore, we must distinguish between forwarding and routing. Forwarding consists of taking a packet at the input and sending it through the output indicated by the table, while routing means the process of making that table.
Physical architecture
Four components can be identified in a router:
- Input ports: performs the functions of the physical layer consisting of the termination of a physical entry link to a router; performs the functions of the data link layer necessary to interoperate with the functions of the data link layer on the remote side of the input link; performs also a search and forward function so that a package forwarded within the commutation framework of the router emerges in the appropriate output port.
- Switching input: connects the ports of entry of the router to its ports of departure.
- Output ports: stores the packages that have been forwarded to you through the switch port and transmits them to the exit link. It then performs the reverse function of the physical layer and the layer of link that the port of entry.
- Lamping processor: executes the ip encamination protocols, maintains the encamination information and the forwarding tables and performs network management functions within the router.
Routing types
Both routers and hosts maintain a routing table. The routing daemon on each system updates the table with all known routes. The system kernel reads the routing table before forwarding packets to the local network. The routing table lists the IP addresses of networks known to the system, including the system's default local network. The table also lists the IP address of a gateway system for each known network. The gateway is a system that can receive outgoing packets and forward them one hop beyond the local network.
Static routing
Small hosts and networks that get routes from a default router, and default routers that only need to know about one or two routers.
Routing determination
The routing information that the router learns from its routing sources is placed in its own routing table. The router uses this table to determine which output ports to use to forward a packet to its destination. The routing table is the router's primary source of information about networks. If the destination network is directly connected, the router will already know which port to use to forward packets. If the destination networks are not directly connected, the router must learn and calculate the most optimal route to use to forward packets to those networks. The routing table is built using one or both of these two methods:
- Manually, by the network administrator.
- Through dynamic processes that run on the network.
Static routes
Static routes are administratively defined and establish specific routes that packets must follow to get from a source port to a destination port. Precise routing control is established based on administrator settings.
Static default routes specify a gateway of last resort, to which the router should send a packet destined for a network that does not appear in its routing table, that is, it is unknown.
Static routes are commonly used in routing from a network to a stub network, since there is only one route in and out of a stub network, thus avoiding the traffic overhead it generates a routing protocol. The static route is configured to achieve connectivity to a data link that is not directly connected to the router. For end-to-end connectivity, it is necessary to configure the route in both directions. Static routes allow manual construction of the routing table.
Dynamic routing
Dynamic routing allows routers to adjust, in real time, the paths used to transmit IP packets. Each protocol has its own methods for defining routes (shortest path, use peer-published routes, etc.).
Dynamic routing algorithms
- Remote Vector: Each router has a table where the best distance is stored and the communication line that should be used to reach the origin.
- State - Client: Discover the neighbors and get the network addresses of these.
Introduction to RIP
RIP (Routing Information Protocol) is one of the oldest routing protocols used by IP-based devices. Its original implementation was for the Xerox protocol in the early 1980s. It gained popularity when it was shipped with UNIX as the routing protocol for that TCP/IP implementation. RIP is a distance vector protocol that uses routing hop count as a metric. RIP's maximum hop count is 15. Any route that exceeds 15 hops is labeled unreachable by setting the hop count to 16. In RIP routing information is propagated from one router to the other neighbors via a IP broadcast using UDP protocol and port 520.
RIP Configuration Process
RIP version one is a classful routing protocol that does not support the publication of netmask information. The RIP version 2 protocol is a classless protocol that supports CIDR, VLSM, route summarization, and security using plain text and MD5 authentication.
Types of routers
Routers can provide connectivity within enterprises, between enterprises and the Internet, and within Internet Service Providers (ISPs). Larger routers interconnect ISPs and these devices are often called metrorouters, and can be used in large company networks
Connectivity in small offices and homes
The routers are used in homes to connect to broadband services, such as IP over cable, ADSL or fiber optics. A router used in a home can allow connectivity to a business through a virtual private network.
Although functionally similar to routers, residential computers use network address translation instead of addressing. This is because instead of connecting local computers directly to the provider's network, a residential router should make the local computers appear to be one piece of equipment.
Enterprise router
Routers of all sizes can be found in enterprises. While the most powerful tend to be found in ISPs, academic and research facilities, but also in large companies.
The three layer model is in common use, not all of them need to be present in other smaller networks.
Access
Access routers, including SOHO, are located at customer sites such as branch offices that do not need hierarchical routing of their own. Usually, they are optimized for the low cost.
Distribution
Distribution routers aggregate traffic from multiple access routers, either at the same location, or from obtaining data streams from multiple sites at a major business location. Distribution routers are often responsible for QoS enforcement across a WAN, so they must have considerable memory, multiple WAN interfaces, and substantial intelligence transformation.
They can also provide connectivity to server groups or external networks. In the latter application, the router's operating system must be careful as part of the security of the overall architecture. Separate from the router may be a firewall or VPN hub, or the router may include these and other security features. When a business is primarily based on campus, there may not be a clear tier distribution, other than perhaps off-campus access.
In such cases, the access routers, connected to a local area network (LAN), are interconnected through the core router.
Core
In enterprises, the core router can provide a "backbone" interconnecting the distribution of router levels to multiple buildings on a campus, or to large local enterprises. They tend to be optimized for high bandwidth.
When an enterprise is widely distributed with no central location, the core router role can be taken over by the WAN service that the enterprise subscribes to, and router distribution becomes the highest level.
Border
Border routers link autonomous systems to Internet backbones or other autonomous systems, they have to be prepared to handle the BGP protocol and if they want to receive the BGP routes, they must have a large amount of memory.
Wireless routers
Although traditionally routers used to deal with fixed networks (Ethernet, ADSL, ISDN...), in recent times routers have begun to appear that allow an interface between fixed and mobile networks (Wi-Fi, GPRS, Edge, UMTS, Fritz!Box, WiMAX...) A wireless router shares the same principle as a traditional router. The difference is that it allows the connection of wireless devices to the networks that the router is connected to through wired connections. The difference between this type of routers is given by the power they reach, the frequencies and the protocols in which they work.
In Wi-Fi these different differences occur in denominations such as class a/b/g/ and n.
Home Equipment
The equipment that is currently sold to the customer as routers is not just that, but is called Customer Premises Equipment (CPE). CPEs are made up of a modem, a router, a switch and optionally a WiFi access point.
This equipment covers the basic functionalities required in the 3 lower layers of the OSI model.
Routers in the OSI model
In the OSI model there are different levels or layers in which machines can work and communicate to understand each other. In the case of routers we find two types of interfaces:
- Interfaces directed: are level 3 interfaces, accessible by IP. Each corresponds to a different subnet address. IOS is called "IP interface". Two subtypes are distinguished in turn:
- Physical interfaces: those accessible directly by IP.
- Virtual interfaces: those that correspond to a VLAN or a CV. If such interface corresponds to a single VLAN is called Switch Virtual Interfaz (SVI), while if it corresponds to a trunk link or a CV, they act as subinterfaces.
- Switched interfaces: these are level 2 interfaces accessible only by the switching module. In IOS they receive the name of switching ports. There are two types:
- Access ports: support only traffic of a VLAN.
- Ports trunk: support traffic of several different VLANs.
These configuration possibilities are only available in modular equipment, since in fixed-configuration equipment, the ports of a router always act as routed interfaces, while the ports of a switch always act as switched interfaces. Furthermore, the only possible ambiguity in configurable equipment occurs in switching modules, where the ports can act in both ways, depending on the interests of the user.
Switches vs. Routers
A switch, like a router, is also a store-and-forward packet switching device. The fundamental difference is that the switch operates at layer 2 (link layer) of the OSI model, so it relies on a MAC address to send a packet, unlike a router that uses the IP address.