How to send multicast message from PC to router to start multicast

[yangfrank]

Dear All

I have a PC and I want to send the video message out through multicast from the PC. Do you think I need to have some special tool installed in the PC to start the multicast ?  The PC is directly connected with a router

Thank you

Frank

[Peter Paluch]

Frank,

To send, or better said, to stream a multicast from a PC, you just need the proper software that performs the streaming itself. If you already have a software that can be configured to send some video content to a multicast destination then you're good.

Understandably, though, your routers must be configured for IP Multicast routing if you want this streaming to be received by stations behind your router. You do not mention whether your network itself is configured for multicast routing - it is not on by default.

Another thing to watch for is the IP TTL value of packets that carry the multicast stream. Quite often, streaming software defaults to TTL=1 to make sure the multicast streaming is never routed off the subnet of the source station (to not pollute the network with streaming). If your receivers are not in the same network as your sender, not only must your routers be configured for multicast routing but you also make sure that the IP TTL is set to a sufficiently high number so that your multicast packets can reach their destination and not perish somewhere along the way because of "TTL Exceeded". Wireshark is your friend here.

You're welcome to ask further! In that case, though, please try to provide more exact information about the stream itself and the location of sender and receivers.

Best regards,
Peter

[yangfrank]

Hi Peter

Thank you so much for your reply! I know that needs the configuration of the router, but I do not know which software I need to install in the PC to send multicast streaming. Can you suggest one or two software for it ? After installing the software in PC, it can send multicast streaming out if the router has a good configuration ? 

Frank

[Peter Paluch]

Hi Frank,

I have personally used the VideoLAN Client (VLC) to do streaming, and it works very nicely if you have a multimedia file ready you want to stream. You can download VLC from its homepage here:

http://www.videolan.org/

This is a multi-feature player and streamer so it has lots of bells and whistles. This video shows, even though in a quite quick succession, how a streaming is set up:

https://www.youtube.com/watch?v=InxO6tviZOE

Specifically stop at 00:27 and check out the command line that is shown in the window. It contains a string similar to this:

{dst=239.0.0.1:1234}

Your string may be different, containing several arguments before and after this, arguments separated by commas:

{arg1,arg2,arg3,...,dst=239:0.0.1:1234,arg4,arg5,...}

You need to add the TTL specifier here so that the stream is sent with a TTL higher than one. You do that simply by editing that line right in the window as follows:

{arg1,arg2,arg3,...,dst=239:0.0.1:1234,ttl=200,arg4,arg5,...}

One more practical recommendation: if your PC has multiple network cards, make sure that only one of them is enabled when doing the streaming. Otherwise, Windows may decide to start streaming out of a different interface than the one you want it to be streamed through. Again, Wireshark is your friend here.

Happy streaming ;)

Best regards,
Peter

[yangfrank]

Peter

It is very helpful and I also found some info in internet due to your suggestion.

Now, I basically know how to initiate multicast due to your reply. But I am not clear about how user to receive the multicast streaming. Usually we just know IGMP can handle the issue, but I do not know how the end user to receive it. For example, user' PC is connect with the end router. Do we need to setup something in the PC to receive the multicast streaming ? How does the PC know there is multicast streaming coming to the PC at its interface which is connected with the router? Thank you

Frank

[Peter Paluch]

Frank,

To receive the multicast stream, you can use VLC again. On the end PC, just start it and tell it to receive the stream at the precise protocol, multicast group address and port you're streaming it to from the source. When you do this, VLC will automatically instruct your end PC to subscribe to the multicast group. This will cause the PC to send an IGMP Membership Report out its interface, telling the routers in its network that there is a subscriber to the particular multicast group. Now, it is up to the routers and the PIM multicast routing protocol to create a multicast distribution tree between the source and your end PC.

So, again - you just need the VLC on the receiver's PC to act as the stream player, and when you tell VLC where's the stream sent to, it will do the necessary IGMP task.

Note that it's IGMP in IPv4, not ICMP, that takes care of stations subscribing and leaving multicast groups.

Best regards,
Peter

[yangfrank]

Hi, Peter

Excellent explanation! The final question: the first router interface which is toward receiver user is configured with "ip pim dense-mode". how about the interface which is connected with source PC ? What I mean is the interface still needs to be configured with "ip pim dense-mode" or other command ? 

Frank

[Peter Paluch · Accepted solution]

Hi Frank,

You are welcome.

To sum up basic configuration rules for your network as simply as possible to make the multicast fly:

1. You need to have an IGP protocol running (OSPF, EIGRP, IS-IS, RIP) on all your routers and make sure that all networks are duly advertised, both the network where the source streamer is, and the networks where the recipients are located. I suppose you already have this.
2. All routers in your network need to be configured with ip multicast-routing global configuration command.
3. All interfaces on all routers in your network need to be configured with ip pim dense-mode interface level command.

By this, I am suggesting that you run a simple, if somewhat inefficient, version of multicast routing in your network, the so-called PIM Dense Mode. More preferred version of multicast would be PIM Sparse Mode but that one is slightly more difficult to properly configure and troubleshoot so let's start with the simplest option and test whether it works.

Once again, be careful to configure all your routers with ip multicast-routing (it's not sufficient to configure just the first or the last router with this command - all routers on the path between the source and receivers need to use this command) and ip pim dense-mode (all interfaces on these routers, both "upstream" interfaces going back to the source, and "downstream" interfaces going toward the receivers).

Best regards,
Peter

[yangfrank]

Peter

Thank you so much for your excellent explanation! I really appreciate your explanation. 

Frank

[Peter Paluch]

Frank,

You are very much welcome. Please keep me posted whether this worked for you. Thanks!

Best regards,
Peter

[yangfrank]

Hi Peter 

I am still a little confused. Please see the diagram in attachment. I read many documents about multicast, but they always explain like the diagram(see original diagram), and never explain the configuration on interface (like R1, F0/2)connecting source PC1 and interface (R4, F0/1)connecting end PC2. My question is that R1 F0/2 and R4 0/1 need to be configured with multicast ? or directly connected with PC1 and PC2 respectively ? 

Frank