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domotile
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Joined: Tue Feb 09, 2021 1:35 pm

SWOS 2.13 IGMP seems to work but it does not

Wed Feb 23, 2022 3:47 pm

Hi Dears,
I am using differnet switches (CRS328-24P-4S+ and CRS318-16P-2S+) all in swos 2.13 for an IPTV based system.
I enabled IGMP snooping on VLAN 10 (IPTV) and checked in IGMP TAB, that the IPTV streams are well distributed along all the switches.
On each switch, the IGMP tab shows me which port is forwarding multicast trafic, and everything is fine.
As soon as a client subrcibes to a multicast stream, the port shows me that the multicast adress changes for the new one.
So aparently everything works pretty well.
But,
If I plugin my computer on an access port on IPTV VLAN and check with wireshark what is going on this port, then I can see that all IGMP streams are comming on that port eventhought no one on the network has subscribed to this stream.
MEaning that IGMP is not used by the switch at all eventhought it seems to.

Has anyone been able to make IGMP work properly on SWOS 2.13?
 
domotile
just joined
Topic Author
Posts: 2
Joined: Tue Feb 09, 2021 1:35 pm

Re: SWOS 2.13 IGMP seems to work but it does not  [SOLVED]

Thu Feb 24, 2022 7:10 am

After deeper investigations, it seems that in fact IGMP really works but...
Just after starting aswitch, this one will send all multicast packets of every stream to all ports on the VLAN. Eventhought no one has subscribed to the stream.
As soon as a client unsubscribes to a stream, then this stream is no more broadcasted to all the vlan ports. And only the subscribers are receiving the multicast stream.
So all I have to do in oreder to have a working IGMP is on a client to parse every channells, then the switch sees unsubscribe IGMP Packets and forwards every streams only to client subcribers.

Pros:
This is nice in one way that if a switch accidentally restarts, the TV channel will be stopped on the subscriber while the switch is off, but as soon as it is on, the TV will receive the stream and display the channel.
Whereas if the multicast was not broadcasted after switch restart, then the TV would not receive the stream after the switch restart as it would not have subscribed to it. The client would have to change the channel in order to subscribe to the stream and receive it once again.

Cons:
If we have a lot of HD streams let's say 100 channels HD,this would generate a trafic of 500 to 600 Mbps to all the ports associated to IPTV VLAN after a restart.
Will every switch handle this? or will we see them crash?

Anyhow, I love Mikrotik

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