Multicast, PIM-SM, and IGMP Snooping

This video describes Multicast, how PIM-SM works, and why IGMP Snooping is important.

[@agaspar9276]

One of the best explanations of Multicast, PIM-SM, and IGMP Snooping

[@BarbaraAnne]

Thank you!

[@RP-xs9ty]

I gotta say this is the best explanation I have ever come across on this.

[@BarbaraAnne]

Thank you! I appreciate that!

[@jonathondavis5513]

Agreed. Thank you for posting this. I found your explanation very helpful.

[@ajko000]

Amazing high level explanation! It really puts into perspective why and how everything works together the way it does.

[@BarbaraAnne]

Thanks!

[@mikkio5371]

nice and well explained !

[@BarbaraAnne]

Thanks!

[@usaiatawakevou6582]

Exactly the explaination im looking for. Simple and easy to understand. Thank you !

[@BarbaraAnne]

Glad it was helpful!

[@obstbrei]

Concise and helpful :) Thank you very much :)

[@BarbaraAnne]

Glad it was helpful! Thanks!

[@ItsRiley3]

This was amazing. Thank you

[@BarbaraAnne]

Thanks!

[@mtnsolutions]

Awesome! thanks so much! keep the videos coming

[@BarbaraAnne]

Thanks Micah!

[@SPJJ72]

Once we are receiving multicast traffic through the RP, it’s possible to switch to the SPT (Source Path Tree). From the diagram , dont see any other alternative paths toward 4 switches.

[@Carcadia_]

Great video Barbara. Just one question, do large scale content delivery companies like Netflix, Stan etc. actually use multicast to deliver packets? These types of companies are always used as multicast examples but do they actually do it that way? I have heard of Netflixes OCA infrastructure but is that just a combination of unicast/anycast?

[@BarbaraAnne]

Thanks Carcadia - with IP TV, everyone is watching the same show at the same time - the exact same packets are being streamed everywhere - that's why you need multicast. For video on demand, through the cable companies or for services like Netflix, those really are more unicast streams. You may be the only person in the world who started that show at exactly that time - there really isn't the need for multicast. For Netflix, it's more important to have video servers closer to the end customers to service the unicast traffic.

[@BeCaffe]

If I understood correctly, PIN-SM (sparse mode) with multiple trees by source would be lighter, generally speaking, as with PIN-DM (dense mode) the traffic is greater in the PIN area as it assumes all the Hosts want the data from the Rendez-vous points. In what scenarios this wouldn't be the case?

[@BarbaraAnne]

Think about a cable company forwarding each channel as a separate multicast group. There's some big sports event happening that everyone is watching. You don't want to be forwarding all the other channels to everyone in the network, as no one is watching. There would be lots of cases where only a few channels are being watched and you don't want to forward the traffic from all the channels. With dense mode, the routers have to keep pruning themselves out of the tree.

[@nico1234abcd]

thanks I finally understand xd

[@BarbaraAnne]

Great! Thanks

[@rifleman542]

The multicast destination mac address displayed on the lower left side of the video is incorrect. The multicast MAC address is a special value that begins with 01-00-5E in hexadecimal. The remaining portion of the multicast MAC address is created by converting the lower 23 bits (in binary) of the IP multicast group address into 6 hexadecimal characters.

[@BarbaraAnne]

Thank you for pointing this out. I meant to discuss the different addressing and forgot to, in the end. I wanted to discuss the numbering in the conversion and how addresses need to be considered carefully when converting IP multicast addresses to Ethernet multicast addresses. As you say, the last 3 numbers in the IP multicast address are converted to HEX but the high order bit in the 2nd IP address number is dropped. Then that HEX number is prepended with 0x010053. Therefore, if you have a multicast IP address of 224.1.0.2 and another with the multicast IP address of 224.129.0.2, they would both covert to Ethernet multicast address HEX 01:00:53:01:00:02. You don’t want 2 Multicast addresses where the last 3 digits are identical except the 2nd number is off by 128 because that will give you the same Ethernet multicast address. Thank you for raising a very good point.

[@amvk99]

Good video, Mutlicast mac seems wrong

[@BarbaraAnne]

Thanks. Ethernet addresses with a 1 in the least significant bit of the first octet are treated as multicast traffic. So the 01: makes it a multicast address. Thanks for the feedback.