Mutlicast Failing without Adding route

John Wood jwood at
Thu Aug 26 18:38:02 UTC 2010

That exactly what I am seeing, with my route added I found that it seems to be working as expected using an external machine running wireshark.  Originally, all I could see was my loopback packet which appeared to have the interface IP so I was not sure if routing was changing the mcast IP to the interface IP but this does not appear to be the case.

Thanks a lot,

From: Till Straumann [mailto:strauman at]
Sent: Thursday, August 26, 2010 2:33 PM
To: John Wood
Cc: rtems-users at
Subject: Re: Mutlicast Failing without Adding route

This may give some insight:

-- Till

On 08/26/2010 12:09 PM, John Wood wrote:
Greetings all,

I am using rtems 4.9.2 on a custom PCB with 2 Ethernet interfaces.  If I don't add a route my multicast sends fail.  Is this the correct behavior?
I am not particularly familiar with multicast.  I have loopback enabled and when I receive the message it has the IP address of my interface as
Opposed to the broadcast address which seems incorrect to me but is it possibly correct.

I tried setting the interface using the IP_MULTICAST_IF but this does not appear to help.

Thanks for any insight,


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