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hatlen
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[SOLVED] SwOS IGMP Snooping hijacking mrouter role!!

Wed Apr 10, 2019 6:52 pm

Hi, all!

Disclaimer: I really don't get multicast and all the terminology, but I do know the IGMP Snooping on Mikrotik kills all TVs up- and downstream, while HP Arubas don't.

On HP (Aruba 2530), I just enable "ip igmp" on the VLAN. Everything works as intended.
On MikroTik, I enable IGMP Snooping on VLAN and also under "System". If anybody knows the difference/correlation, please do enlighten me.

Anyhow, the huge problem. When I turn both these checkboxes on (one on vlan + under System tab), the Mikrotik takes the role as Mrouter on my core router upstream! I see this on the Cisco core C6509e, and suddenly the Mikrotik, currently CRS317, takes the role as mrouter. (Command on Cisco: show ip igmp snooping mrouter, returns the interface where the MT switch is. With only 1 TV connected.) What's up with that? Now all the TVs in my entrire network, up- and downstream, tries to ask the Mikrotik for TV channels, which obviously breaks the whole TV system.

When turning off IGMP snooping, all TVs up- and downstream works again, but now downstream from MT it's going to flood multicast, which is kinda what IGMP should stop.

Isn't this really PIM, Layer3-stuff, and not L2 IGMP Snooping? Or is there a L3 IGMP snooping, and that's what MT uses?
UPDATE: It's IGMP Querier role, which is a L3/L2 role..

Can anyone please tell me how to just enable L2 IGMP Snooping without breaking hundreds of TVs again? Thanks in advance!
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Last edited by hatlen on Wed Apr 24, 2019 1:32 pm, edited 1 time in total.
 
hatlen
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Topic Author
Posts: 4
Joined: Wed Dec 06, 2017 10:26 am

Re: [SOLVED] SwOS IGMP Snooping hijacking mrouter role!!

Wed Apr 24, 2019 10:10 am

SwOS acts as a querier when set in IGMP Snooping-mode. This is confirmed from MikroTik support per April 15th 2019;
Currently, SwOS will act as an IGMP querier when IGMP Snooping is enabled and there is no option to disable this. We are planning to add a configurable IGMP querier option within the SwOS and some other options for further SwOS releases, but I cannot provide any ETA yet.
After doing some packet capturing I can also see that it sends out IGMP Querier messages from the IP 0.0.0.0, which makes it take priority over any other IGMP Querier in the subnet. This is picked up upstream and therefor breaks multicast for the entire broadcast domain.

Hope this helps others.

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