Subject: RE: [MMUSIC] specifying the multicast interface

From: "Matthew Heaney" <[email-masked]>
Date: Fri, 17 Oct 2003 12:41:27 -0400

> -----Original Message-----
> From: Magnus Westerlund [mailto:[email-masked]] 
> Sent: Friday, October 17, 2003 10:13 AM
> 
> I have some problem of understanding why you need to specify the 
> outgoing interface to use. Is this multihomes servers that 
> you have an 
> interest of ensuring that the transmissions are made using the right 
> sender address? A little more explanation on the needs and 
> advantages to 
> specify the sending interface would be appreciated. Especially if we 
> should consider adding anything to the RTSP standard.

I don't know the exact reasons why our customer asked for the feature,
but we do have machines here with two interface cards.  In our case each
card is on a completely different network.  

Suppose a client on one network is interested in joining the multicast
session.  If the server does not specify the local interface from which
to send, then do we have any guarantee that the datagrams will reach the
client?  (I still have to run this test.)  

Suppose the "default" interface (the one chosen by the kernel if we
don't explicitly specify) is the one attached to the other network.
Does this mean that the client (who isn't on the network to which the
"default" interface is attached) doesn't ever see any of those packets?

It just seems odd that RTSP allows you to specify the TTL
(IP_MULTICAST_TTL), but provides no way to specify the local interface
for sending (IP_MULTICAST_IF) or whether local loopback occurs
(IP_MULTICAST_LOOP).

> Then I would also recommend you to skip the "X-" from your parameter 
> name, as if it would be standardized in the future you don't have to 
> change the implementations, to also support the new name. The only 
> consideration is that if someone in the future registers this name is 
> that the proprietary use are responsible for updating there 
> feature or 
> giving it a new name.

Server mods are easy enough for me.

I just realized, though, that it might be nice to allow the admin user
to specify either the IP of the interface or its name.  Maybe I need to
two headers?  Here are some ideas:

interface
local-interface
multicast-interface
interface-address
interface-name
multicast-interface-address
multicast-interface-name
etc

-Matt

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---

From: Tom Marshall <[email-masked]>
Date: Fri, 17 Oct 2003 10:00:52 -0700

> for sending (IP_MULTICAST_IF) or whether local loopback occurs

I'm not really familiar with your application, but our server is written to
always use the same interface for the transport and control connections. 
This should solve the problem of the "default" interface.  Do you or your
customer have other reasons for wanting to specify the interface?

-- 
Beware of Programmers who carry screwdrivers.
        -- Leonard Brandwein