Hello,

The Wiki says that using multicast-helper=full will make the DST-MAC to be changed to the one of the receivers wlan interface, allowing it to be send at max modulation.

I have an AP with 27 CPE conected to it, and say 5 of them use multicast OSPF packets. If the DST-MAC gets replaced from a multicast one to the one of the receiver, how many copies of the same multicast packet will travel through the air? As I see it, 5 of them will fly from the AP, one for each DST-MAC.

Anyone can shed some light about this?
Thanks a lot.

Why only five copies? If you have 27 clients connected, I would expect 27 unless some other process exists to alter the forwarding of the multicast traffic, like IGMP. I don't know of anything that exists on Mikrotik to change the forwarding, so I would expect one multicast packet -> 27 unicast data packets, with 802.11 ACKs, and possible retries. This is data amplification.

If you can sniff wifi traffic, you would see this process and know for sure. Even if you can't sniff from an external device, a Mikrotik can usually sniff this wifi traffic if you have an extra radio.

If you don't use multicast-helper=full, the DST-MAC of a multicast packet should be multicast type MAC (i.e. 01:00:5E:00:00:00 for OSPF) and wireless interface will only send ONE copy of the packet regardless of how many conected clients it has, albeit at the slowest basic rate set on the AP.

To overcome that limitation, multicast-helper can be used but I just don't know how many copies will travel by the air in that case. I was wondering if multicas-helper would somehow "filter" and send multicast packets only to the stations that may need it.

In the 27 stations example, supposing that a multicast packet will be sent 27 times regardless of how many stations do need that packet (i.e. suppose just two use OSPF), I think it's better to not use multicast-helper and send 1 packet at slowest rate than sending 27 copies of it.

Where is multicast helper located?
I purchased a hap to use as a customer cpe for multicast specifically, and can't find the helper under advanced wireless any where...
I even tried to update it to whatever teh current latest build is, and that bricked the unit. So now I'm really out of luck.

Where is multicast helper located?

It is at the bottom of the "Wireless" tab in the wireless interface settings dialog. If you don't see it make sure you have switched to Advanced Mode (click the "Advanced Mode" button on the right side of the same dialog).

Alternatively, you can set it via command line at /interface wireless set wlan1 multicast-helper=full

Multicast package must be installed

Pretty sure i added that package. Either way i bricked it after an update to the latest rc. No links lights now. Its in the garbage can.

Multicast package must be installed

I do not believe this is correct - Multicast package is for PIM and IGMP Snooping.

This topic is relating to OSPF Multicasts and Wireless handling of the packets.

In Winbox under Wireless you need to enable the advanced button to see the Multicast settings.