# Where's the multicast data?

## zzaappp

I did a fresh install on a new machine using Gentoo 2005.1 on a box using INTEL PRO NIC cards. A tcpdump shows streams of multicast data on all 3 devices, but only 2 of the 3 devices is allowing the multicast data to come through to userland applications.

I have tried a number of things - swapping cables, moving the cards around, changing out all the INTEL cards for Syskonnect. But the problem persists: I can get multicast data from only 2 of the 3 devices at any one time.

My old installation used a gentoo 2004 release; 2005.1 had big changes in /etc/conf.d/net.

Could there be a problem with the new network configuration? Garsh sakes, I just don't see how. How can promiscuous mode show the data, but userland only be able to get at multicast data on 2 of 3 devices?

I'm out of ideas. I have multicast turned on in the kernel. Is there something I need to do on a per-device basis to get multicast through to userland?

Suggestions?

-z

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## magic919

Sounds like a possible quirk/feature/bug of the kernel.  

But first a few Qs.  Are you checking that multicast is on?  Just because promisc mode can see it but no means ensures that the IF is listening for it under normal circumstances.  I'm assuming ifconfig will show this up.

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## mrtsufo

Thank you for the reply.

The bug has been found.  It is an IRQ conflict between 1 of the three NIC cards.  All of the cards come up.  The one card in question shows data is going to the card (via ifconfig), but we couldn't get to it.

Because of this issue, I started another thread to see if there was anyway to change the IRQ number assigned to that NIC card remotely (through the Gentoo side).  We may end up swapping out that machine, though I wish there was another solution.  We don't have the ability to see the BIOS on this box.  Just bad luck.

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