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

Sat Jan 18, 2020 6:57 pm

Is there any way to turn off querier on switchos but leave IGMP snooping on? I'd like to actually put an actual RP so don't want the switch to be a querier, but would like to have IGMP Snooping on to avoid multicast -> broadcast.
 
hatlen
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Re: [SOLVED] SwOS IGMP Snooping hijacking mrouter role!!

Mon Jan 20, 2020 10:17 am

Is there any way to turn off querier on switchos but leave IGMP snooping on? I'd like to actually put an actual RP so don't want the switch to be a querier, but would like to have IGMP Snooping on to avoid multicast -> broadcast.
No, that is exactly the problem here. I do believe it might work on routerOS though, but I cannot say as I haven't tried. But it does NOT work on SwitchOS. It's on MikroTik's "ToDo"-list, but noone knows when it'll get fixed.
 
dreamnet
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Re: [SOLVED] SwOS IGMP Snooping hijacking mrouter role!!

Tue Jun 02, 2020 8:22 am

Any news about fuxing this bug?
Interesting , but on older revisions of RB260gs or RB250 ( NOT CSS106xx ) IGMP snooping working perfectly , without hijacking mrouter role.
 
RobstarUSA
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Re: [SOLVED] SwOS IGMP Snooping hijacking mrouter role!!

Thu Jun 04, 2020 6:35 pm

I actually have turned IGMP snooping back on my CRS317.

Cisco switches have a bug that let 0.0.0.0 win the querier election see CSCub33602

As per RFC4541:

b) The arrival port for IGMP Queries (sent by multicast routers)
where the source address is not 0.0.0.0.

The 0.0.0.0 address represents a special case where the switch
is proxying IGMP Queries for faster network convergence, but is
not itself the Querier. The switch does not use its own IP
address (even if it has one), because this would cause the
Queries to be seen as coming from a newly elected Querier. The
0.0.0.0 address is used to indicate that the Query packets are
NOT from a multicast router.

After upgrading my cisco switches and turning igmp snooping back on & setting one as the querier, everything is working fine for me.

0.0.0.0 is a valid source address for an IGMP query, but should never win an election as per the above RFC. If your switch lets 0.0.0.0 win the election you need to have the switch manufacturer fix it.
 
4920441
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Re: [SOLVED] SwOS IGMP Snooping hijacking mrouter role!!

Sun Jun 07, 2020 3:48 pm

I actually have turned IGMP snooping back on my CRS317.

Cisco switches have a bug that let 0.0.0.0 win the querier election see CSCub33602
That is not the only problem when connecting a(at least a) CSS326 which only runs SwOS 2.11 to a trunk port of a DELL 7024 Switch which already has an IP Address in the same VLAN and a manually set up querier 1.1.1.2 - the same thing happens.
You see on the dell that the Mikrotik Joins, the Mikrotik says it snooped the Multicast Addresses and then the Mikrotik sends IGMP Leave messages to the dell and the connection faints away -
BUT the CSS 326 still thinks he's jonied correctly and receives something, which isn't the case. (You cannot see much in the Webinterface, only waht is displayed in the IGMP tab)

The most annoying thing is, that Mikrotik does not do anything about its strange behaviour in bigger Environmets with other switches.
Even more annoying is, that you could buy a 20 $ Netgear GS105E which works flawlessy from the beginning, though it can only handle Multicast on a single (but chooseable) VLAN...

Cheers

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

Mon Jun 08, 2020 2:58 am

The Mikrotik should only be forwarding leave messages, not sending them itself. Are you sure the subscriber didn't send the leave message? AFAIK You can't do a static join on switchos. Perhaps the best way to do it is to turn off all IGMP on SwitchOS. Then in theory it should "work" even though it will just broadcast everywhere.

I have another unrelated problem....I was troubleshooting all this because of miniupnpd plugin (opnsense). When the daemon starts on opnsense, I see it send traffic to 239.255.255.250 but never actually join the group. I had to create a static join on the switch port itself for upnp to actually work......argghhh...

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