Multicasting is the networking technique of delivering the same packet simultaneously to a group of clients. IP multicast provides dynamic many-to-many connectivity between a set of senders at least 1 and a group of receivers. The format of IP multicast packets is identical to that of unicast packets and is distinguished only by the use of a special class of destination address class D IPv4 address which denotes a specific multicast group.
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Unlike broadcast transmission which is used on some local area networks , multicast clients receive a stream of packets only if they have previously elect to do so by joining the specific multicast group address. Membership of a group is dynamic and controlled by the receivers in turn informed by the local client applications. The routers in a multicast network learn which sub-networks have active clients for each multicast group and attempt to minimise the transmission of packets across parts of the network for which there are no active clients.
The multicast mode is useful if a group of clients require a common set of data at the same time, or when the clients are able to receive and store cache common data until needed. The majority of installed LANs e. Ethernet are able to support the multicast transmission mode.
The earliest LAN network interface cards had no specific support for multicast and introduced a big performance penalty by forcing the adaptor to receive all packets promiscuous mode and perform software filtering to remove all unwanted packets. Most modern network interface cards implement a set of multicast filters, relieving the host of the burden of performing excessive software filtering. The Ethernet network uses two hardware addresses which identify the source and destination of each frame sent by the Ethernet.
Each computer network interface card is allocated a globally unique 6 byte address when the factory manufactures the card stored in a PROM. This is the normal source address used by an interface. A computer sends all packets which it creates with its own hardware source address, and receives all packets which match its hardware address or the broadcast address.
When configured to use multicast, a selection of multicast hardware addresses may also be received. So I have a message. I give it to the morse code operator.
Understanding Ethernet MAC Addresses
He sends it. The message is given to my friend. My friend nor I understand morse code. I would not agree with you about a couple of things. First of all, there are big differences between how the hubs and the switches operate, hubs would not ever be able to distinguish between a broadcast or a multicast frame, neither a unicast one, hubs flood the frame out of all its ports without being able to read the mac addresses, instead switches are able to, and they flood the frame out of all its ports except the port on which the frame has been received if it is a broadcast frame, and to the interested ports only in case of a multicast frame.
That decision would depend on the destination mac address used inside the frame. The other thing is that switches "speaks" mac address language, meaning that the switch forwards the frame based on the destination mac address not the ip address.
MAC Address Mapping
The fact that a device on the network would answer to the arp request with its mac address tied to its ip address would not mean that the switch would be able to pass any frame to the ip address, instead it does still comunicate via mac addresses, because what the switch would learn is the mac address of that device not its ip address and will know on which port it would forward frames sent to that device connected to it. To external ports, and to the internal port towards the internal IP level, if it exists. For a proprietary MAC control plane, I would not be surprised that there are some exceptions.
Advanced switches perform a trick called IGMP snooping. When a PC issues a IGMP join request the switch makes a note so he knows that there is a multicast client on the port. So when a multicast packet arrives on the switch it knows only to send it to the specific port. Broadcasts will go to all ports in the VLAN.
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Please type your message and try again. Oct 18, 6: Hi Can anyone plz tell me the difference between multicast ethernet frames and broadcast ethernet frames?? This content has been marked as final. Show 12 replies. Broadcast Frame: Then the multicast frame is the same as a broadcast frame ,then why different terminology?? Hi SN Pretend switches are hubs so do nothing except send the frame to everybody. Every PC sees the frame. It looks at the destination MAC.
If broadcast passes it to IP.