Networking devices (HUB,SWITCH,ROUTER) are responsible for unicasting/multicasting/broadcasting ?

[pankajdav]

Networking devices (HUB,SWITCH,ROUTER) are responsible for unicasting /multicasting /broadcasting ?

[Peter Paluch]

Hi,

Can you perhaps clarify your question?

When you talk about unicasting/multicasting/broadcasting, it is not entirely clear what you mean by these terms. Keep in mind that the categories of "unicast", "multicast", and "broadcast" refer first to how a datagram (a frame or a packet) is intended to be delivered (unicast = precisely one recipient, multicast = a precise group of recipients, broadcast = everyone). This in turn influences what address is used as the destination address, and finally, how network devices take care of delivering this datagram. However, the choice of whether the datagram is going to be a unicast, multicast, or broadcast is made by its sender, not by the network. The sender decides whether it wants to talk to a single recipient, a group of recipients or to anyone, and then sends its datagram accordingly. Network devices such as switches and routers only take care of delivering that datagram to its appropriate recipient(s), but they do not change the type of the datagram anymore - unicast stays unicast, multicast stays multicast, broadcast stays broadcast.

Best regards,
Peter

[pankajdav]

I Heard that, Hub do broadcast,switch do multicast and router do  broadcast.

i want to know the correct answer.

[devils_advocate]

Peter has given you the correct answer, its not as simple as saying that one 'does' each.

[Peter Paluch]

Hello,

Oh, I see what you mean. What you refer to is a popular explanation of how networking devices work, but it is not very precise.

A hub takes a signal coming in through one of its ports, regenerates it and sends it out through all remaining ports, regardless of who is the intended recipient of the transmission. The resulting effect is that a hub is "broadcasting" all received data; however, a hub does not understand the data nor the addressing - it is a Layer1 device and it is concerned only with signals - and is simply flooding the signal everywhere. Everyone connected to the hub receives all data passing through the hub as if the hub was "broadcasting", but the hub has no idea about unicast/multicast/broadcast frames. What it does is broadcasting the signal, and as a direct consequence, broadcasting the data encoded in it. Once again, the way a hub operates has nothing to do with frame addressing.

Switches and routers pay attention to the addressing of received datagrams - switches check frame addresses (MAC addresses), routers check packet addresses (IPv4/IPv6 addresses). Depending on the actual destination address, each of these devices makes a forwarding choice and either forwards the datagram through a single path, or it replicates it and sends it on multiple paths. Delivering data through switches and routers is therefore controlled, not unrestrained as with a hub.

Would this explain your question? Please feel welcome to ask further!

Best regards,
Peter

[Joseph W. Doherty]

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Posting

Just wanted to add a note that switches, if they don't know where to send a unicast or multicast (for non-IGMP snooping switches) frames, behave like a hub, i.e. they flood the frame to all their ports, except the ingress port.  (NB: on a VLAN capable switch, all ports within the same VLAN).

Routers, however, if they don't know where to send a packet, drop it.  Also, switches flood broadcast frames while routers generally drop broadcast packets.

So, as Peter has noted, hubs replicate everything, but switches and routers analyze ingress frames/packets, and depending on their configuration, and state, determine whether to forward the frame or packet, and if they do forward it, they also determine how it will be forwarded.