Undoubtedly, the best multicast explanation available on the Internet. I was hooked for straight 4-6hrs of back to back videos... Awesome stuff.. Will definitely check out other videos... Channel name is very apt... Decoding Packets indeed!!!
It's been 14 years since I have been into networking and I was always afraid of it due to its complexity but your videos makes it piece of cake. Thanks for such a high quality content.
Awesome video for sure ! A true reference for those who want to deep dive into this complex protocol! I haven't see explanation about "PIM Forwarder" or "Designated Forwarder" . When more than one routers are making the Last Hop Segment, which router forwards the stream to the final receiver. Speaking about LHS , since Snooping switches only have a single Querier port , all Join/Leave will be sent to this querier port , therefore to the Designated Querier ( by default elected with lowest IP) , which by nature will be different from the designer Router ( elected by highest IP ?) .. so it becomes quite likely that the Designated querier is a different router than the designated Router.. How is it possible to have one router getting the information about the receiver interest (IGMP) and the other sending the PIM Join to the RP ? Thanks for your answer, and sorry if this piece of info was already n your video, I could not find it.
Excellent series on Multicast. quick question at 13:12, you mention that the destination field in the IP header will be the RP address but before you also mentioned that the source and destination will be the source address and destination will be the mcast group so how does the inital IP header packet with S,G in source destination field inside the PIM register message get translated to the source and RP as destination IP. Thanks
Hi I have a question regarding the Null Register Message. In the steady state the traffic is flowing down the S,G tree and RP is already learning about the S,G in the data plane then why do we need Null Register Message in the steady state?
No problem but the original comment is still valid within the context of slide 105. It was incorrect in that video. I have added a reply to your original comment indicating the same.
Great video! I have a question about RP decision: if RP does not have a (*,G) state yet, and there are two different sources connected to two different FHRs which register these sources, what will happen when PIM Join is received for (*,G) on RP? Will RP try to send PIM Join towards both sources? MC traffic from which source will the RP forward down the (*,G) tree?
Yes, as long as the sources are registered for the same Group as the one signalled in the RPT (*,G). If that happens to be the case, then the RP will initiate an STP (S,G join) to both the sources. It will also forward the streams from both the sources on the *,G tree towards the receiver. The receiver is then essentially receiving two multicast streams.
Mike Condon The RP has a timer/timeout associated with the Register state (S, G) which is reset every time the Null Register message is received. If the reception of these messages ceases for a time longer than the timeout, the state is simply discarded by the RP. HTH.
You rock. Such quick replies! One followup for clarity. When you say the state is discarded, you mean the (S.G) is removed from the RP? Correct? Actually, now I had a scenario pop up in my head. Maybe you can share your insight. the (S,G) is well established, MC traffic is flowing, and steady-state null register messages are happening between the FHR and RP. MC traffic continues to flow, but for some reason the null register messages are getting lost inbetween the FHR and the RP. When the RP times out the null register messages and removes the (S,G) will it not take into account there is incoming MC traffic for that (S,G) or will it not care, remove the (S,G) state, and start discarding the MC packets? Thanks again for your amazing series!
Mike Condon No problem. I like to help out as much as my time allows. Short version - Correct. Longer version - we need to qualify your statement by stating if the S, G state was a result of the Registration process alone, then you are correct. But suppose the RP was in the path of an S, G and the state was on the RP was a result of PIM Join message, then no. But in the very simple case where there are no receivers and the state was caused by registration alone, your assumption remains correct.
In all your lectures and the example, you always mentioned the receiver wishes to join the (*, G) group. And if I understand ICMPv3 correctly, it allows receiver to signal LHR to join a (S,G) group. What happens then? Does LHR (DR) sends a PM join message to the RP? If yes, would all the intermediate MHR nodes create (S,G)? Would really appreciate if you could explain that example. Thank you.
The videos on the channel so far only discuss Any Source MC or ASM. Once we go into the IGMPv3 realm and the receiver signals the intent to join a specific source, the router essentially has to run SSM or Source Specific Multicast. SSM does not have a concept of an RP or (*,G)/RPT because they are no longer needed. The LHR knows about the S from the get go so it can send S,G Joins directly towards the S. All the MHRs will then only have the S,G and no notion of *,G. HTH.
Undoubtedly, the best multicast explanation available on the Internet. I was hooked for straight 4-6hrs of back to back videos... Awesome stuff.. Will definitely check out other videos... Channel name is very apt... Decoding Packets indeed!!!
Thank you for your kind words. I am glad you are finding the content useful.
It's been 14 years since I have been into networking and I was always afraid of it due to its complexity but your videos makes it piece of cake. Thanks for such a high quality content.
Awesome video for sure ! A true reference for those who want to deep dive into this complex protocol!
I haven't see explanation about "PIM Forwarder" or "Designated Forwarder" . When more than one routers are making the Last Hop Segment, which router forwards the stream to the final receiver.
Speaking about LHS , since Snooping switches only have a single Querier port , all Join/Leave will be sent to this querier port , therefore to the Designated Querier ( by default elected with lowest IP) , which by nature will be different from the designer Router ( elected by highest IP ?) .. so it becomes quite likely that the Designated querier is a different router than the designated Router.. How is it possible to have one router getting the information about the receiver interest (IGMP) and the other sending the PIM Join to the RP ? Thanks for your answer, and sorry if this piece of info was already n your video, I could not find it.
Excellent series on Multicast. quick question at 13:12, you mention that the destination field in the IP header will be the RP address but before you also mentioned that the source and destination will be the source address and destination will be the mcast group so how does the inital IP header packet with S,G in source destination field inside the PIM register message get translated to the source and RP as destination IP. Thanks
Hi I have a question regarding the Null Register Message. In the steady state the traffic is flowing down the S,G tree and RP is already learning about the S,G in the data plane then why do we need Null Register Message in the steady state?
Love it!!
Ignore my comment in Lecture 8. I think you addressed the slide error LHR -> FHR error :)
No problem but the original comment is still valid within the context of slide 105. It was incorrect in that video. I have added a reply to your original comment indicating the same.
Great video! I have a question about RP decision: if RP does not have a (*,G) state yet, and there are two different sources connected to two different FHRs which register these sources, what will happen when PIM Join is received for (*,G) on RP? Will RP try to send PIM Join towards both sources? MC traffic from which source will the RP forward down the (*,G) tree?
Yes, as long as the sources are registered for the same Group as the one signalled in the RPT (*,G). If that happens to be the case, then the RP will initiate an STP (S,G join) to both the sources. It will also forward the streams from both the sources on the *,G tree towards the receiver. The receiver is then essentially receiving two multicast streams.
Great, thank you very much for such a quick reply!
You are very welcome.
Great series, it has helped me a lot.
Quick question, what does the RP do if it stops receiving null register messages from the FHR? Does it care?
Mike Condon The RP has a timer/timeout associated with the Register state (S, G) which is reset every time the Null Register message is received. If the reception of these messages ceases for a time longer than the timeout, the state is simply discarded by the RP.
HTH.
You rock. Such quick replies!
One followup for clarity. When you say the state is discarded, you mean the (S.G) is removed from the RP? Correct?
Actually, now I had a scenario pop up in my head. Maybe you can share your insight.
the (S,G) is well established, MC traffic is flowing, and steady-state null register messages are happening between the FHR and RP. MC traffic continues to flow, but for some reason the null register messages are getting lost inbetween the FHR and the RP. When the RP times out the null register messages and removes the (S,G) will it not take into account there is incoming MC traffic for that (S,G) or will it not care, remove the (S,G) state, and start discarding the MC packets?
Thanks again for your amazing series!
Mike Condon No problem. I like to help out as much as my time allows.
Short version - Correct.
Longer version - we need to qualify your statement by stating if the S, G state was a result of the Registration process alone, then you are correct. But suppose the RP was in the path of an S, G and the state was on the RP was a result of PIM Join message, then no.
But in the very simple case where there are no receivers and the state was caused by registration alone, your assumption remains correct.
In all your lectures and the example, you always mentioned the receiver wishes to join the (*, G) group. And if I understand ICMPv3 correctly, it allows receiver to signal LHR to join a (S,G) group. What happens then? Does LHR (DR) sends a PM join message to the RP? If yes, would all the intermediate MHR nodes create (S,G)? Would really appreciate if you could explain that example. Thank you.
The videos on the channel so far only discuss Any Source MC or ASM. Once we go into the IGMPv3 realm and the receiver signals the intent to join a specific source, the router essentially has to run SSM or Source Specific Multicast.
SSM does not have a concept of an RP or (*,G)/RPT because they are no longer needed. The LHR knows about the S from the get go so it can send S,G Joins directly towards the S. All the MHRs will then only have the S,G and no notion of *,G.
HTH.