Routers are the critical part of all the networks and can be both security aid and security vulnerability. A router basically has more network interfaces through which network traffic is forwarded. Or it might be blocked. The router decides when to forward packets between the networks based on internal routing table.
Routers connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router.The term “layer 3 switch” often is used interchangeably with router, but switch is a general term without a rigorous technical definition. In marketing usage, it is generally optimized for Ethernet LAN interfaces and may not have other physical interface types.
Routers operate in two different plane:
1) Control plane:= in which the router learns the outgoing interface that is most appropriate for forwarding specific packets to specific destinations,
2) Forwarding plane:= which is responsible for the actual process of sending a packet received on a logical interface to an outbound logical interface.
Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network, electronic data networks (such as the Internet), and transportation (transport) networks. This article is concerned primarily with routing in electronic data networks using packet switching technology.
Routing, in essence, is the act of finding a path from one place to another on which a packet can travel. To find this path, we need algorithms. They will generally be distributed among many routers, allowing them to jointly share information.
Routing is said to contain three elements:
* Routing protocols:= the things that allow information to be gathered and distributed
* Routing algorithms:= to determine paths
* Routing databases:= to store information that the algorithm has discovered. The routing database sometimes corresponds directly to routing table entries, sometimes not.