IGMP Version 2

Lessons Discussion
1

This topic is to discuss the following lesson:

2

Rene,

Great lesson, I have a question about 224.0.1.40 what is that IP address? I heard in the video you mentioned it is an auto rp. What is RP and why we need this? Please clarify.

 

Hamood

 

3

Hi Hamood,

PIM is the protocol we use between multicast-enabled routers to forward multicast traffic, it has three modes:

- sparse
- dense
- sparse-dense

When we use any of the two sparse modes, we use a central point in our traffic where we forward multicast traffic to. This is called the RP (Rendezvous Point).

This RP can be statically configured or it can be learned through auto RP.

Auto RP uses the 224.0.1.40 multicast address.

Once I write about the PIM modes, I’ll cover this in detail.

Rene

4

Thank you… Rene. It is a great tutorial. May I ask if you have a tutorial on bidirectional pim?

5

You are welcome Vicchester. I don’t have one yet but I’m currently working on multicast material…stay tuned :slight_smile:

6

Hi Rene,

First of all, thank you for this easiest way to explain this cours,
I have some questions, i would like to know what

Updating EXCLUDE group timer for 239.1.1.1

and

Switching to INCLUDE mode for 239.1.1.1 on GigabitEthernet0/1 means exactly.

I know that the first one is when there is still some members for the groupe and the second one is when no more member is interested for this group, but i didn’t understand the meaning of ‘EXCLUDE’ and ‘INCLUDE’

Also, do you use a switch between the PCs and the router ?

Thank you

7

Hi Ismail,

Include and exclude mode are used in IGMP version 3:

  • Include mode means that the receiver announces that it wants to join a certain multicast group but ONLY from the specified IP addresses.
  • Exclude mode means that the receive announces that it wants to join a certain multicast group but NOT from the specified IP addresses.

It seems the debug output for IGMP version 1/2/3 is the same.

I’ve explained this a bit in this lesson:

IGMP Version 3

I did most of these examples in VIRL so the client (another router) was directly connected to the router.

Rene

8

Hi Rene,

Thank you for your response,
So the “include” and “exclude” debug don’t make sense for IGMP2 ?

9

That’s right. Only IGMPv3 is able to request multicast traffic from certain sources.

10

hi thank you for your article

as i see this post, i have a one question

in this situation, if host 2 was silently shut off, how does the switch delete igmp snooping table?

if host1 was silently shut off, host2 don’t receive igmp membership report because of longer mrt, host2 send igmp memgership report message to router…

in the situation that hosts with longer mrt was silently shut off, how do the switches delete igmp snooping table???

thanks

11

Hi Mungi,

It is explained in the IGMP snooping lesson. Take a look at the “Maintaining Groups” section.

IGMP version 1 has the same issue as you describe, there are no group leave messages. IGMP snooping will have to rely on the general query / report mechanism.

Rene

12

Hi Rene,

Have a question. In the diagram mentioned, the router interface is connected to a segment where two hosts are connected? Is the segment here is nothing but a switch?

13

Hello Ananth.

That’s exactly right. The segment is nothing but a switch. This is confirmed by the fact that the router interface and both hosts are in the same subnet.

I hope this has been helpful!

Laz

14

Hi Rene,
Have Question about report suppression.
If both hosts within same multicast group (239.1.1.1) wants to receive the multicast traffic then both will send membership report, but why only HOST1 with lower MRT is able to send membership report and other host2 can not (as it receives membership report from other host1)
I think it is required for each host to send membership report to receive multicast traffic.
In above case if HOST 2 won’t send report (as it receive report from HOST1) to router then how it will receive the traffic.

Please advise.

thanks.
Amit

1 Like
15

Hi Rene,
Have Question about report suppression.
If both hosts within same multicast group (239.1.1.1) wants to receive the multicast traffic then both will send membership report, but why only HOST1 with lower MRT is able to send membership report and other host2 can not (as it receives membership report from other host1)
I think it is required for each host to send membership report to receive multicast traffic.
In above case if HOST 2 won’t send report (as it receive report from HOST1) to router then how it will receive the traffic.

Please advise.

thanks.
Amit

1 Like
16

Hi Rene,
Thanks for your valuable effort as always :slight_smile:

I have one question, why we will put the command “ip pim sparse-mode” on user connecting port as we know PIM Protocol is used to route Multicast Traffic between Multicast Router but no PIM router on the end on port Fa0/1. just like OSPF no need to enable ospf on port(we can but not mandatory) that there is no OSPF router on the other end . Please clarify me once again dear .Thanks

br/zaman

17

Hi Zaman,

Enabling ip pim sparse-mode on the interface will do the job but there is a “risk” that you form PIM neighbor adjacencies.

If the interface connects to end users, it is better to use the ip pim passive command. This will still process IGMP packets but it won’t send or receive PIM packets from other routers (and thus not form neighbor adjacencies with other routers).

When you use the passive command, your router automatically becomes the DR for the segment so you have to be 100% sure there are no other PIM routers on that segment, or you will have duplicate PIM messages that are sent upstream.

18

hi mr Rene!!!
my internet or in the company which i work when i open the page the place of video or diagram gives an error message message and does not display what should i do case there will be lots of good points in the video but other contents is working good some time it brings the vidoe

19

Hi @mozamel-ccie,

Which error message do you see? Any chance you can share a screenshot?

21

I have bit confusion about IGMP V1 and V2 , as we know that V1 and V2 has different ways of query and membership so what how it works in Dense and sparse mode , if we use Spare-mode with IGMP V1 so what would be the tree shape ?? . RP is there due to spare-mode but with IGMP V1, so even in the presence of RP still the there would be flooding and pruning due to IGMP V1 , this is the point of confusion for me .

Regards…