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
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