20 June 2013

HUB, SWITCH and ROUTER


 HUB: - 

This is the least intelligent device on the network. It copies the packet arrived on one port to all of its other ports except the port that it came from. So there is no difference in broadcasting and a normal packet.

If computers are connected in bus topography and if that line is connected to hub, all the computers on that bus reads the packet which is placed by hub at the same time which mean the packet travels to the end of the bus replicating a copy to each node on the bus.

SWITCH:- 

A switch does essentially what a hub does but more efficiently. By paying attention to the traffic that comes across it, it can "learn" where particular addresses are. For example, if it sees traffic from machine A coming in on port 2, it now knows that machine A is connected to that port and that traffic to machine A needs to only be sent to that port and not any of the others. The switch now records the IP or MAC in its table.

If any multicast packet or a packet (MAC or IP) which is not known to it arrives on the port it replicates that packet to all its ports except the port that the packet arrived from.

 The net result of using a switch over a hub is that most of the network traffic only goes where it needs to rather than to every port. On busy networks this can make the network significantly faster.

ROUTER: -  

These are the most intelligent and complex devices on the network. It routes the packet according to the routing table recorded in it. It also may add additional headers to the packet for efficient routing.

When ever it routes the multicast packet to another network it reduces the packets TTL by one. When the TTL becomes 0 the packet will no more be forwarded by the router. It drops the packet. 
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