wifi Multicast flood

RouterOS General
1

Hello!

Resume of my setup:
hAP ax2
ether1 WAN
ether 2, 3, 4, 5, wifi1 and wifi2 BRIDGE

PPPoE over vlan6 for internet
vlan2 for IPTV
vlan3 for VoIP
(Movistar Spain)

For IPTV, we need IGMP Proxy, with vlan2 upstream and bridge downstream. IGMP Snooping enabled on bridge.

As I have the TV Box connected via wifi1 (5Ghz), multicast-enhance is enabled on that interface.

I can see some strange behavior with that setup, that I think isn’t correct. At least, it doesn’t happen with my Asus router.

For example, if I am seeing a live TV channel, and I see an Rx rate of 7Mbps on vlan2 and ether1, wifi1 has a Tx of that 7Mbps multiplied by number of devices connected to the interface. Let’s say I have the TV Box, my iPhone and my Macbook in wifi1. So Tx on wifi1 is 21Mbps.
If I use Wireshark on my Macbook, I can see all UDP multicast packets coming in.

I think only TV Box should receive that traffic. Am I right?

2

That feels like a bug.

I think the Mikrotik radio should likely have its own multicast subscriber list and send it to only its subscribed stations.

3

Yes, I think the same.

4

Tested with 7.14.3, 7.15.2 and 7.16beta4. Same results. Reported to support.

5

This sounds like expected behavior - if you look at the help filehttps://help.mikrotik.com/docs/display/ROS/Wireless+Interface,


full - all multicast packet mac address are changed to unicast mac addresses prior to sending them out

It doesn’t say anything about a filter. I think what you want is a link for this function to something like an IGMP snooping table but I don’t think it exists. So adding more clients will increase the amount of traffic since each multicast frame is then copied to each client individually. Multicast-to-unicast conversion doesn’t scale for this reason. In small amounts it can overcome some issues with 802.11 group traffic but nothing is free. Another option: do a high density WiFi design so you can have a high minimum basic rate setting and disable the unicast conversion. That will reduce the net impact of transmitting group traffic at low basic rates and allow only a single group frame to be sent.

6

So, maybe the Asus do a trick? I can’t see the multicast traffic in my laptop when using the Asus.

To mitigate that, I’ve created a virtual SSID only for the TV Box.

7

So, maybe the Asus do a trick? I can’t see the multicast traffic in my laptop when using the Asus.

Maybe, would be interesting to know. Can you get an OTA packet capture (monitor mode)? Behavior would be clear with a good capture to compare what they are doing. Doesn’t need to be decryptable since the destination mac addresses are not encrypted in the wireless frames.