The VideoLAN Forums

I've been working with vlc for some time now, and have successfully set up multiple multicast streams in a home environment, which could succesfully be received on multiple other hosts on this network. Vlc makes this quite easy, but I've had some trouble setting up playlists with multiple items, since it seems to be impossible to to change your streaming settings without readding the item.

However, I'm now trying to do the same on a larger (switched) network with approx. 1500 hosts. Althought interested parties could receive my streams without any problems, it soon became apparant (to the dismay of the network administrator), that the stream was broadcasted to every host.

I've been reading up a bit on the specifications of ip multicasting. It seems that the way multicasting is handled, would be something like this:
* multicast server creates a multicast group based on its multicast adress.
* an interested client joins the multicast group.
* an IGMP request is sent from switch to (upstream) switch, until the server has been reached. Switches that receive this request are being set up to forward multicast packets to the switch that isssued the request until the client is reached.
(the documentation I found mentioned only routers, but it would seem logiscal to assume that this also goes for switches)

now, my problem is, where and why does this multicast stream turn into a broadcast?
Is my assumption incorrect and do switches just pass multicast traffic to any interface, or should something be set up in the switch? I read that multicast support for ip4 is not mandatory; does this mean that the switch should support multicast or would otherwise turn the multicast into a broadcast?

The ip I used was in the 239.13 range; I'd do a retry in the 239.255 range, which seems to be recommended in e.g. http://www.29west.com/docs/THPM/multica ... nment.html

I don't think however that this is the source of the problem. At this point I'm looking for someone that has a bit of experience on setting up multicast streams in a larger network, that could direct me to the correct line of inquiry. Thanks for your time reading this post, I hope you could shine a light on my issue

(PS -- some other small issue I noticed is that the VLM does not seem to accept windows' file paths (with colons and backslahes) as valid ones; I did not see another topic about this, so I wondered if this a known issue. I use six VLC instances at this point for 6 different streams)

Setup:
network: mostly 3com 3300's on a bigIron BI8000; Between the streaming server and the bigIron, there's also a Nortel Baystack 450 and an Avaya P550.
I use VLC version 0.8.5 on windows XP pro with all relevant updates. There is no 3rd party firewall installed and the windows firewall is turned off at this point.

Any hint is appreciated

However, I'm now trying to do the same on a larger (switched) network with approx. 1500 hosts. Althought interested parties could receive my streams without any problems, it soon became apparant (to the dismay of the network administrator), that the stream was broadcasted to every host.

This is what is supposed to happen. At the switch layer, broadcast==multicast. The streams will flood to all ports like any other broadcast.

* an interested client joins the multicast group.
* an IGMP request is sent from switch to (upstream) switch,

Switches are generally layer 2 devices. A IGMP is a layer 3 (IP) level thing. Routers look at IGMP, not layer 2 switches.

(the documentation I found mentioned only routers, but it would seem logiscal to assume that this also goes for switches)

Switch != router, but a router may work by hardware switching.

now, my problem is, where and why does this multicast stream turn into a broadcast?
Is my assumption incorrect and do switches just pass multicast traffic to any interface, or should something be set up in the switch?

You need switches that do 'IGMP snooping'. I do not know if the switch models you mention can do this. It will probably need to be enabled if they do, it may not be done by default.

My network is a nearly 'pure' cisco environment - where all the switches support a propreitory Cisco protocol call CGMP. The router (a cisco processes the IGMP packets as you would expect, but additionly it builds forwarding tables it sends to the switches via this CGMP thing.
Some of our switches also do 'IGMP Snooping' and work out the forwarding themselves.

With out such layer 3 snooping, or a switch-router communication protocol, the layer 2 switches have no choice but to flood multicast data to all ports, as the switch has no way of learning who is actually listening. This is what you are seeing happen.

You may need to replace/upgrade your switches.

Thanks for your comments -- As you may have noticed, network administration at this level is not in my daily routine

I've been able to find out that IGMP snooping is turned on on at least the local switch (the nortel baystack). The main problem seems to be about the BigIron, which brings the multicast signal to every one of the 64 fiber lines -- we will test the igmp snooping feature there later today. I'll keep you posted

Because of some constraints, I was only able to test it in a separate environment, but I got things working the way they should. The config for the bigIron will be changed later on; thanks for solving the problem