All around the world people using internet for different purposes generally says for information purpose that can be in the form of email, image text, animation etc. whenever you send email to a person it reach to the destination, although there are millions of nodes attached with the internet. Truly said, Internet is made up of router, router is the machine which moves the packet from source to destination, basically router is a processing machine which moves the packet (Protocol data unit at third layer, network layer) among different network.
Router works at network layer of OSI or internetwork layer of TCP/IP model. The router has the ability to process the protocol data unit called packet. Packets enter through the router incoming interface consist of multiple fields in packet header but the field which are most important are packet source and destination IP address. All the routing decision depends upon these two fields. Router consist of IOS (operating system of router) for configuration purpose, user can statically configure packet path or enable the routing protocol such as RIP,IGRP,EIGRP,ISIS etc to exchange updates packets for dynamically update routing table when any change in configuration or topology occurs.
Routing table or forwarding table is database of the router all the destination network addresses are stored in it. Router compares destination address of packet with the table entry and check out whether destination address is directly connected or it should be forwarded to next router or next hop. Most of the time there are multiple path for the same destination, router find the optimal path based on the metric used by the routing protocol.
Routing protocol enable in the IOS of the router calculates the routing metric based upon hop count, distance, delay and bandwidth etc. RIP routing protocol uses hop count; less the number of hope count better the path.
Router can be accessed remotely by telnet, remote updates related to the router health and changes in configuration can be received by Simple network management protocol (SNMP).Router not forward the broadcast of data link layer that the reason it is used in the VLAN for interVlan routing purpose.