Multicast on loopback?

Multicast on loopback?

Post by Erik G. Burrow » Thu, 15 Feb 2001 08:03:23



In developing multicast applications, I would like to be able to test
locally over the loopback interface. This does not work without adding a
bogus route statement to get the kernel to hand up the packets from
loopback to my waiting application.

This route statement is not necessary with other network drivers, so I
assume that adding some logic to the loopback driver would fix this
problem. Is it possible to get this added?

-Erik G. Burrows

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Multicast on loopback?

Post by Alan Co » Thu, 15 Feb 2001 08:12:09


Quote:> locally over the loopback interface. This does not work without adding a
> bogus route statement to get the kernel to hand up the packets from
> loopback to my waiting application.

The multicast ABI includes the ability to toggle loopback of multicast
datagrams. Use the socket options instead

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Multicast on loopback?

Post by Erik G. Burrow » Fri, 16 Feb 2001 04:16:21


Quote:> > locally over the loopback interface. This does not work without adding a
> > bogus route statement to get the kernel to hand up the packets from
> > loopback to my waiting application.

> The multicast ABI includes the ability to toggle loopback of multicast
> datagrams. Use the socket options instead

I read that multicast loopback is by default enabled, and I have witnessed
this, when having my application bind to my ethernet interface, but the
datagrams do not seem to be looped back when I bind to the 'lo' interface.

Could this possibly be a conflict with the inherently 'looped back'
behavior of the loopback net driver?

As far as toggling the flag, or even reading it, I cannot, as I am
developing in Java.

For developing, I can easily kludge it to work, by adding a fake route
statement, forcing the packets back up to the application, but I want to
make sure the differing behavior is not a bug in the kernel networking
code.

-Erik G. Burrows

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Multicast on loopback?

Post by Alan Co » Fri, 16 Feb 2001 04:54:04


Quote:> I read that multicast loopback is by default enabled, and I have witnessed
> this, when having my application bind to my ethernet interface, but the
> datagrams do not seem to be looped back when I bind to the 'lo' interface.

I wouldnt expect them to be. The lo interface does not support multicasting.
I dont think this is a bug

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1. multicast packet on a loopback address

Hello:

    I have a question about the sequence of operations I am trying out.

    This is on a Linux box.

-  A UDP server is started on the local machine listening on address
INADDR_ANY and port 9001.

-  A socket is created and bound on the 'loopback' address (127.0.0.1)
and on port 9002.

-  The server socket has an option set to listen to multicast address.

    The client (bound on loopback address) sends data on the machine's
IP address. This data is received at the server. The client then sends
data on the multicast address to which the server is listening to. The
server does not get the multicast packet.

    If the same program is run on SOLARIS the multicast packet is
received.

    Here are my questions -

1)  Can I send a multicast packet on a socket bound on the IP loopback
address.

2)  If yes, then does LINUX implement this functionality.

3)  If I get the packet on the server, how can I find out if it came on
the multicast address or on the unicast address.

    I know that I am setting the server socket options correctly,
because when I bind the client to the local IP address and send the
multicast packet the packet is received at the server.

Thanks for your answers and time.

Regards,

Chinmay
(I dont speak for my company in this email)

Sent via Deja.com http://www.deja.com/
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