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I've been dealing with a persistent network loop for the past month, trying different things. Now I see in one of my network interfaces that it recorded 1.6 million multicasts, and roughly half a million broadcasts. Can these cause network loops? And how do I solve this?

Device: Mikrotik RouterBoard 2011UAiS

The interface on which there's the most Multi- and Broadcasts is the one with Omnitik sender dish installed on.

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(As seen here, I don't have any standalone L2 switches)

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If multicasts or broadcasts caused network loops, they wouldn't exist or be used by anything.

I've seen buggy off-brand network equipment mishandle multicasts and broadcasts by sending them back on the port they came in on, which would initially look to an observer to be a lot like a network loop. Maybe look to see if your OmniTik or something else is doing that.

Because this buggy behavior is generally done by devices acting as bridges/switches (including APs), and because such devices forward frames without modifying the frames' source or destination MAC addresses, you can't blame the devices that own those MAC addresses without additional evidence.

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  • Of course multicast can loop, it's easily done in an non IGMP snooped environment. Without traffic capture I cant comment on what's going on in the above setup. But multicast can absolutely loop, I've seen it taking down large backbones when it happens.
    – Intenso
    Commented Jan 5, 2017 at 17:32
  • @Intenso The question was whether multicasts could cause network loops. Not whether or not they could ever loop on a broken network. Of course multicasts will loop in a loop-connected, non-STP network.
    – Spiff
    Commented Jan 6, 2017 at 0:46

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