Re: [mh] Audrey Question - FIlter Multicast Packets

[Jim D. <ji...@du...>]

Michael,

When I start sending multicast packets into my local network, the 
audrey's, on the same network, have trouble playing sounds from a 
misterhouse server on the same network.  When I stop the multicast 
traffic, the audreys work fine.

I know that it's truly multicast traffic, sent by a pulseaudio server, 
sending rtp traffic to address 224.0.0.56.  I can see the traffic in 
tcpdump.

I'm assuming that the little audrey usb adapters are not filtering the 
multicast packets in hardware, as I would expect them to, and sending 
them into the QNX network stack on the audrey itself.  The little usb 
network adapters must be either operating in promiscuous mode (which I 
doubt) or have decided that broadcast and multicast addresses are 
similar (which it shouldn't).

In any event, the multicast traffic is causing the audrey's to misbehave.

I could solve this problem by purchasing a managed 10/100 switch, to 
replace my unmanaged switch, and use the manager to block the multicast 
packets to the audrey ports.  This would cost money :-(

I could also solve this problem by creating another "audrey" subnet and 
using my misterhouse server as a router and block the traffic that way. 
  I do have a spare networking interface I could use for that.

I was hoping that someone might have seen this issue and found a way to 
resolve it by using either a switch on the audrey io-net command or 
using some other filter in the audrey networking command, or some other 
switch for the usb network adapter.

Thanks for all the information.  It could be as simply as purchasing a 
different brand of usb network adapter.  I'll look into that aspect.

Jim

Michael Stovenour wrote:
> Generally there is no way to filter multicast or broadcast on a LAN segment.
> Some switches have a "snooping" feature that allows them to learn which
> ports are interested in the multicast packets, but AFAIK, none of the
> consumer grade switches will do this.
> Normally the MAC layer hardware in the LAN adaptor will be "armed" by the
> software to only receive MAC addresses that are interesting to the software
> applications.  The card's own MAC address and the broadcast address
> (ff:ff:ff:ff:ff:ff) are normally the only ones armed.  True multicast
> traffic uses a completely different set of MAC addresses specifically
> associated with the multicast groups.  Most LAN adaptors will not receive
> those packets, or bother the higher software layers, unless the software
> layers specifically tell the MAC layer to listen to one or more of the
> multicast MAC addresses.  Listening for "all" MAC addresses is called
> promiscuous mode on most adaptors and familiar to folks that run ethereal or
> wireshark.
> If the Audrey hardware is designed like most other LAN adaptors, then this
> would imply that the Audrey will not even hear the multicast traffic.  What
> I don't know is if the USB adaptors generally perform this filtering in
> hardware and if there are better adaptors that can filter locally.  This
> functionality is so fundamental to Ethernet that I have a hard time
> believing that any Ethernet implementation would push this into software.
> Are you sure these packets are multicast and not broadcast
> (ff:ff:ff:ff:ff:ff)?  If they are broadcast then I would say that the
> application generating them is badly written.  Application writers must
> understand that a broadcast packet causes extra work by "every" Ethernet
> device on the network because the upper software layers are notified of the
> packet and must decide if the packet requires any action.  Applications like
> xAP/xPL create a CPU "tax" on every Ethernet device on the network
> regardless of their interest in the protocol.  A better implementation is to
> use multicast because then only the applications that are interested in the
> packets are armed to process them eliminating the CPU tax on those Ethernet
> nodes that are not interested in the packets.
> 
> Michael
> 
> -----Original Message-----
> From: mis...@li...
> [mailto:mis...@li...] On Behalf Of Jim
> Duda
> Sent: Saturday, April 19, 2008 12:11 PM
> To: mis...@li...
> Subject: [mh] Audrey Question - FIlter Multicast Packets
> 
> Does anyone know if there is a way to disable multicast packets on the 
> Audrey?  I have some multicast traffic on my local LAN which appears to 
> be overwhelming my audrey(s).  I'm wondering if there is a way to filter 
> them out in the external USB adapter?
> 
> Jim
> 
> 
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