Looking for IGMP (multicast) server-client solution
Hi, I have following issue to solve: The network have one server which sends multicast streams to several multicast groups. I would like it to stop streaming if no client is listening, and start streaming again when client is joining multicast group. I see from sniffing, that clients indeed send IGMP join group protocol message , and I wonder how to make linux server to handle this join and manage multicast group. I saw that kernel have provisions to manage multicast groups through setsockopt(), but I did not find how to get join/leave group notification at user space. I know that there are multicast routers , like mrouted and pimd and I am trying to configure thema at they moment but I doubt that I can configure only one interface because it contradict routing concept, isn't it ? Thanks , Lev = To unsubscribe, send mail to [EMAIL PROTECTED] with the word unsubscribe in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Looking for IGMP (multicast) server-client solution
On Mon, Sep 22, 2008 at 11:38 AM, Lev Olshvang [EMAIL PROTECTED] wrote: Hi, I have following issue to solve: The network have one server which sends multicast streams to several multicast groups. I would like it to stop streaming if no client is listening, and start streaming again when client is joining multicast group. Normally for multicast the server never receives any notification if there are clients or not. It just sends data and if the clients want it, they ask for it. To control the server actual sending you need an external protocol to notify the server that there is a new client and when the client leaves. If the clients are connected to the server without a router between them, you could implement a program that listens on the interface for the IGMP messages and controls the server when to send and when not. If there is a router between the server and the clients you are out of luck as the router expects the multicast packets to just be sent constantly to its interface for it to consider this multicast group active at all. A router will not send IGMP messages to you! I see from sniffing, that clients indeed send IGMP join group protocol message , and I wonder how to make linux server to handle this join and manage multicast group. If you send data to the interface the clients will receive it, I'm not sure what is your problem statement here. I saw that kernel have provisions to manage multicast groups through setsockopt(), but I did not find how to get join/leave group notification at user space. I know that there are multicast routers , like mrouted and pimd and I am trying to configure thema at they moment but I doubt that I can configure only one interface because it contradict routing concept, isn't it ? mrouted and pimd will monitor for IGMP messages and control the kernel multicast routing fabric. They will instruct the kernel where to forward multicast packets, but you only need that if you have multiple interfaces on your computer or to make a multicast router that sits between your multicast server and clients. If the server app is on a machine and the clients are connected to it directly (as in with a switch or a hub) you don't need mrouted. Thanks , Lev Baruch
Re: Looking for IGMP (multicast) server-client solution
Hi Baruch, Thanks for response, I will put my comments close to your statements, please see below Thaks, Baruch Even wrote: On Mon, Sep 22, 2008 at 11:38 AM, Lev Olshvang [EMAIL PROTECTED] wrote: Hi, I have following issue to solve: The network have one server which sends multicast streams to several multicast groups. I would like it to stop streaming if no client is listening, and start streaming again when client is joining multicast group. Normally for multicast the server never receives any notification if there are clients or not. It just sends data and if the clients want it, they ask for it. To control the server actual sending you need an external protocol to notify the server that there is a new client and when the client leaves. As such, I think IGMP serves this matter. IGMP defines host - router conversation and I see IGMP messages from a host (in my terms client). ( client application use setsockopt( IP_ADD_MEMBERSHIP) ) . The server box have as linux kernel + mrouted counting for this groups and making proper entries in /proc/net/igmp, /proc/net/ip_mf_cache ,... If the clients are connected to the server without a router between them, you could implement a program that listens on the interface for the IGMP messages and controls the server when to send and when not. Since the kernel have this information - which group are active on every interface, it is very logically to suppose that kernel may easily filter out the multicast packets to the non-active group. It seems to me it should work this way. But these functionality should be implemented in kernel space ( it is similar to netfilter,) the question is how to turn it on ? If there is a router between the server and the clients you are out of luck as the router expects the multicast packets to just be sent constantly to its interface for it to consider this multicast group active at all. A router will not send IGMP messages to you! I think you wrong here, I see mrouted is taking the responsibility of querier and periodically ask the interface neighbours to confirm every registered multicast group relationship. I see from sniffing, that clients indeed send IGMP join group protocol message , and I wonder how to make linux server to handle this join and manage multicast group. If you send data to the interface the clients will receive it, I'm not sure what is your problem statement here. I do not want to overload LAN in a data nobody is interesting (no clients running) I saw that kernel have provisions to manage multicast groups through setsockopt(), but I did not find how to get join/leave group notification at user space. I know that there are multicast routers , like mrouted and pimd and I am trying to configure thema at they moment but I doubt that I can configure only one interface because it contradict routing concept, isn't it ? mrouted and pimd will monitor for IGMP messages and control the kernel multicast routing fabric. They will instruct the kernel where to forward multicast packets, but you only need that if you have multiple interfaces on your computer or to make a multicast router that sits between your multicast server and clients. I expected them to turn outgoing packet filtering on the base of active group information kernel has. If the server app is on a machine and the clients are connected to it directly (as in with a switch or a hub) you don't need mrouted. Thanks , Lev Baruch = To unsubscribe, send mail to [EMAIL PROTECTED] with the word "unsubscribe" in the message body, e.g., run the command echo unsubscribe | mail [EMAIL PROTECTED]
Re: Looking for IGMP (multicast) server-client solution
On Mon, Sep 22, 2008 at 1:39 PM, Lev Olshvang [EMAIL PROTECTED] wrote: Hi Baruch, Thanks for response, I will put my comments close to your statements, please see below Thaks, Baruch Even wrote: On Mon, Sep 22, 2008 at 11:38 AM, Lev Olshvang [EMAIL PROTECTED] wrote: Hi, I have following issue to solve: The network have one server which sends multicast streams to several multicast groups. I would like it to stop streaming if no client is listening, and start streaming again when client is joining multicast group. Normally for multicast the server never receives any notification if there are clients or not. It just sends data and if the clients want it, they ask for it. To control the server actual sending you need an external protocol to notify the server that there is a new client and when the client leaves. As such, I think IGMP serves this matter. IGMP defines host - router conversation and I see IGMP messages from a host (in my terms client). ( client application use setsockopt( IP_ADD_MEMBERSHIP) ) . The server box have as linux kernel + mrouted counting for this groups and making proper entries in /proc/net/igmp, /proc/net/ip_mf_cache ,... Yes. If the clients are connected to the server without a router between them, you could implement a program that listens on the interface for the IGMP messages and controls the server when to send and when not. Since the kernel have this information - which group are active on every interface, it is very logically to suppose that kernel may easily filter out the multicast packets to the non-active group. It seems to me it should work this way. But these functionality should be implemented in kernel space ( it is similar to netfilter,) the question is how to turn it on ? It has it but multicast routing doesn't work this way. There is no way to turn it on simply because there is no such functionality. The multicast sender will continue to send its data on the output interface regardless of any routing rules. The routing rules can only add additional interfaces to send to. If there is a router between the server and the clients you are out of luck as the router expects the multicast packets to just be sent constantly to its interface for it to consider this multicast group active at all. A router will not send IGMP messages to you! I think you wrong here, I see mrouted is taking the responsibility of querier and periodically ask the interface neighbours to confirm every registered multicast group relationship. That's the router-client communication. I meant that the router will not send the multicast sender an IGMP join request. I see from sniffing, that clients indeed send IGMP join group protocol message , and I wonder how to make linux server to handle this join and manage multicast group. If you send data to the interface the clients will receive it, I'm not sure what is your problem statement here. I do not want to overload LAN in a data nobody is interesting (no clients running) Then the case is closed. Implement your own protocol on top to notify the server when to stop transmission. There is one way you can try but it's likely not to work. If you send your data to a tun device that has no output or a loopback device it might be that mrouted will properly forward from it to the external interfaces when clients show up there but the multicast sender will continue to send and burn cpu time, you just won't see the output on the network. I saw that kernel have provisions to manage multicast groups through setsockopt(), but I did not find how to get join/leave group notification at user space. I know that there are multicast routers , like mrouted and pimd and I am trying to configure thema at they moment but I doubt that I can configure only one interface because it contradict routing concept, isn't it ? mrouted and pimd will monitor for IGMP messages and control the kernel multicast routing fabric. They will instruct the kernel where to forward multicast packets, but you only need that if you have multiple interfaces on your computer or to make a multicast router that sits between your multicast server and clients. I expected them to turn outgoing packet filtering on the base of active group information kernel has. That never happens. Baruch
