Multicast troubleshooting

[ddod]

I have three machines trying to connect to a multicast stream. All three machines are running windows XP and have the same version of VLC installed. They are also all sitting on the same subnet and none of them are running a firewall. However only one out the three will play multicast streams using VLC. I have not been sure where to start the troubleshooting since multicast is a fairly new topic for me. I started with sniffing the traffic using ethereal. All three behave very differently. The address we want to access is 239.25.16.X. They all start out by sending a dns query based on the multicast address (ie, Standard Query AAAA 239.25.16.X.domain.com) which of course return nothing.

The one that works then sends an IGMP V2 Membership Report packet to the specified multicast address. After that packet VLC start playing the video and I see the UDP video packets in my sniff with the source IP being the video source and the destination being the multicast address.

Client 2 (which does not work) sends an IGMP V2 Membership Report packet to the multicast address 239.255.255.250. It keeps trying again with the same packet and nothing. No video ever appears. VLC just sits there.

Client 3 (which also does not work) sends an IGMP V3 Membership Report packet to the multicast address 224.0.0.22. It keeps trying again with the same packet and nothing. No video ever appears. VLC just sits there.

I have no idea what would be causing these three machine to behave so differently. Any ideas?

Thanks.

[kellysp]

Are all three servers connected to the same switch or are they spread across a network?

IGMP is the message protocol used to notify the network a device wants to join a group/stream or is a source for a group/stream. This IGMP packet should be received by the local router so it can send a PIM message to the rest of the network requesting the multicast stream your server requested. If two of the three server are not receiving the video than the IGMP message is not getting to the router. Check that multicast is enabled on the switch and upstream router. After this you will need to verify the switch and router are receiving the igmp packet.

Thanks
Shawn

[ddod]

Thanks for the response. All three are connecting to the Cisco switch on the same port (via local netgear switch). IN other words all three machines are sitting right next to each other. The packets I described below are the packets being sent by the clients to the router. One client is sending the correct packet which the router can and does respond to. The other clients are sending th wrong information. The question is not whether the router is configured correctly but why the machines are all behaving differently. How does VLC make the multicast request. Does it build and send the packet itself or does it trust some underlying windows API. If the second is the case, these API is responding differently to the same VLC request. SO the question is, how can we reconfigure the boxes so that they respond appropriately.

Once again thanks for your response.

[ddod]

I have discovered the problem. One solution was pretty simple, it involved users that had configured their Cisco VPN to have its stateful firewall on at all times, even when they were not using it.

The second was a simple fix in XP but is proving a bit more difficult in VIsta. It was effecting machines with multiple interfaces (physical and virtual). In XP, ensuring that the main interface (with access to the multicast feeds) was set as the first priority in the binding order fixes the problem. In Vista, that doesn't seem to have any effect. It seems to be choosing the interface on it owns, somehow. Which inevitably is the wrong interface. Now I can go in and change the routing table to give the interface I want a higher priority (giving the route a lower metric) and that fixes the problem as well. However, I need to discover a simpler solution for my end users. Any ideas?

It seems likely to me that this is a bug in Vista. Is there any possibility that this might be a VLC issue though?

Thanks.