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milsty
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Joined: Thu Apr 23, 2020 3:37 pm

Multicast routing issue on RB3011

Thu Apr 23, 2020 3:53 pm

Hello,

For more than two weeks I am struggling to turn on reliable multicast routing on RB3011. By reliable, I mean that I expect the router to not lose packets. I tested everything available on RouterOS in this matter and in any case the router loses some packets (between 0.1% and 0.01%). The configuration was tested on 6 concurrent streams of IPTV channels. The thing that bothers me the most is that RouterOS does not report any packet loss on any interfaces.

The issue was discovered by mirroring input and output traffic with Wireshark. The output streams lacked some of the packets which were available at the input.

Thank you in advance for any suggestions.
 
pwuk
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Posts: 51
Joined: Wed Aug 01, 2012 8:51 pm

Re: Multicast routing issue on RB3011

Tue May 12, 2020 6:21 pm

I've seen Juniper SRXs silently dropping unicast traffic. I haven't got any concrete proof that mikrotiks are dropping packets silently, but I've suspected. I do know some routers - like the CCR1036 - are prone to reordering packets, especially when there are queue trees involved.

I'm glad someone else is looking into packet loss at low levels.

I boot a lot of multicast traffic around via mikrotiks over wan links (3rd party mpls etc links), rarely see packet loss. Looking at one 20mbit stream over a BT EAD (so 170 million packets a day), I last had one lost packet (ignoring reordering) on 5th April, so no loss. Looking for the last 26 billion packets over this year, total of 294 lost packets - 1 in 90 million, all on April 5th apart from 7 on April 5th, almost certainly something dodgy with the fibres. That is with a CCR 1036, but does confirm that you shouldn't be seeing such high loss with routeros as a whole.

If I send a 400mbit stream through a 2011 (I don't have a 3011) in software switching mode, I get occasional packet loss in iperf, and that's without any firewall rules. At a lower bitrate (say 10x10mbit streams) I don't see losses in unicast UDP mode. In Multicast, I see some loss with multiple streams, but single stream again is fine.

Is your loss regular (so 1 ever 50,000 packets), or is it clumpy (say 10 losses in a row every 500,000 packets)

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