A router is an interconnection equipment computer networks to ensure the routing of packets between two or more networks in order to determine the path that a data packet will take.
When a user calls a URL, the Web client (browser) queries the name server, which shows him in return the IP address of the target machine.
Her workstation sends the request to the nearest router, that is to say, the network default gateway on which it is located. This router will thus determine the next machine to which the data will be routed so that the chosen path is the best.
To do so, the routers keep updated routing tables, a real mapping of routes to follow in relation to the intended address. There are many protocols dedicated to this task.
In addition to their routing function, routers are used to manipulate the data flowing in the form of datagrams to ensure the transition from one type of network to another. But since the networks do not have the same capabilities in terms of size of data packets, routers are tasked with fragmenting packets to allow their free movement.
Appearance of a routerThe first routers were simply computers with multiple network adapters, each of which was connected to a different network. Current routers are mostly hardware dedicated to the routing task, usually in the form of 1U servers.
A router has multiple network interfaces, each connected to a different network. It thus has many IP addresses from different networks on which it is connected.
Wireless RouterThe principle of a wireless router is the same as that of a conventional router, except that it allows wireless devices (WiFi stations for example) to connect the networks to which the router is connected by wire connections (typically Ethernet).
Routing algorithmsThere are generally two types of routing algorithm:
- The type of router distance vector (distance vector) Establish a routing table identifying calculating the "cost" (in terms of number of hops) for each of the routes and then transmit that table to neighboring routers. At each connection request router selects the least expensive route.
- The type of router link state (link state routing) Listen to the continuous network in order to identify the various elements which surround it. From this information each router calculates the shortest path (in time) to neighboring routers and distributes this information in the form of packet update. Each router then builds its routing table by calculating the shortest paths to all other routers (using the algorithm Dijkstra).
- Routing principle
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