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List:       netbsd-tech-net
Subject:    Re: multicast on interfaces which don't support it
From:       Ignatios Souvatzis <ignatios () theory ! cs ! uni-bonn ! de>
Date:       2003-01-06 10:24:24
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Hello,

On Sat, Jan 04, 2003 at 06:56:33PM +0100, Pavel Cahyna wrote:

> Would be possible to emulate the missing
> multicast support by setting promiscuitous mode and selecting only those
> packet that are relevant? I've heard Linux does this. This may apply to
> Ethernet also.

I can't tell what Tokenring hardawre or the the specific card can do, but in
NetBSD, this would be a function
of the network hardware driver (e.g., the hardware driver would need to count
the number of multicast addresses, enable promiscuious receive mode if > 0, 
and set the IFF_MULTICAST and IFF_ALLMULTI modes. 

The filtering is then done at the network (e.g. IP, IPv6) level. It is done
anyway because even multicast-filtering hardware does no perfect filtering,
but hasing, and so is leaking.

Somebody please corret me if I'm wrong.

	-is

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