Stupid multicast question

RouterOS General
1

I’ve never trusted multicast I’m afraid, so don’t have any experience of how it’s supposed to work, other than vague notions of magic. It would, however, simplify one project I’m working on

I have 2 mikrotik 1100AHs, linked together with a single gigabit cable on ether1, making about 15 of the ports into a simple bridged network

I am transmitting a 12mbit video stream from ether2 on mikrotik 1, and I’m subscribing on another port on router 2 on ether3

All works fine.

However if I look at the traffic stats on ether4 on mikrotik 1, or indeed any other port in the bridge on either mikrotik, I see a 13mbit transmission. It’s effectively being broadcast.

Is that correct?

I don’t need to route the traffic, but would like to avoid the broadcast if possible, mainly as I was hoping to have a total of about 60mbit of multicast traffic floating around and some devices on the network are only 100mbit. An alternative would be to redo the network to remove the 100mbits and place on another subnet, but as it’s 4000 miles away from where I am, and 6000 miles away from home, that would be a bit risky.

(Both routers Running MikroTik RouterOS 6.1 (c) 1999-2013 http://www.mikrotik.com/)

Thanks

2

you can create router topology over bridges using tunnels, for example EoIP, and pass multicast data over the tunnels. Because bridge in RouterOS adhere to RFC request - all multicast packets should be sent out on all ports except ingress.

3

If the setup is static and you simply want to dump the traffic on ports where it is not required you could use bridge filters.

Some layer 2 switches use higher layer helper apps like IGMP snooping to determine which ports actually need the multicast traffic.

4

there is a little problem with snooping - it is not governed by any standard, so all vendors of snooping can choose how to brake IGMP/multicast and any of them does that in their own way.