Multicast very slow



  • So, trucking along with Fog. Now trying multicast.

    I’ve got the one Fog server, which unicasts flawlessly. Network is flat, hooked up via numerous Netgear GSM7248v2 switches. These all have IGMP snooping and query enabled, as thats what I’ve seen recommended for multicast.

    Unicast speeds are approx 3.5 GiB/min to the client.

    Multicast speeds are approx 3.4 MiB/min to the clients.

    I’ve replaced all network cables that can be easily replaced (switch patch cords, cords to clients, etc) with new to verify them. Did a cable check on the main links between the switches, all come up fine. All cables are Cat6 or better.

    Any suggestions to try?


  • Developer

    To a certain point, yes multicast is faster in performance, but it uses UDP with broadcasting all the “image’s” packets across your network. Unicast uses TCP directing the traffic to that particular machine. If on a separate network you will not see any issues either way. If on the same network (using multicast) you will find that your “bandwidth” will be effected throughout the entire network.



  • http://fogproject.org/wiki/index.php?title=Multicasting
    The information is the same due to a merge of the pages.[/quote]

    That’s what I’m doing right now, mostly. and honestly, it works. I just hoped with Multicast it would take less time.


  • Developer

    You could also run unicast in groups. Connect them all to the switch, register, add them all to “group1”, and tell the group to download.

    Multicast is http://fogproject.org/wiki/index.php?title=Multicasting
    The information is the same due to a merge of the pages.



  • 2 clients, since this was just a test. I tried two different ones, in a different chunk of the building on a different switch, same result.

    Unicast is uniformly fast. I haven’t ran into one that is slower. We’re gig across the board, and it has helped out alot.

    that was my understanding of Multicast too, either 100% or nothing. Hence the confusion.

    I’ll dig through the troubleshooting. For now, I’m just Unicast and queing, but doing a whole group in one shot would be fantastic. We’re 1:1 laptops, and I’d love to be able to hook up a whole room to the switch,s tart, go for coffee, and come back.


  • Developer

    How many clients? Did you try different clients? Just two as a start…

    Is unicast fast with each and every single client?

    From my experience multicast just does NOT work if configured incorrectly but it wouldn’t be a bottleneck. Please correct me if someone has got a different voice on this.

    Maybe this is of any help too: http://fogproject.org/wiki/index.php?title=Troubleshooting_a_multicast


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