Subject: Re: setting ethernet interface hardware address?
To: Kevin Lahey <>
From: Jason R Thorpe <>
List: tech-net
Date: 10/17/2001 11:07:30
On Wed, Oct 17, 2001 at 10:47:44AM -0700, Kevin Lahey wrote:

 > I remember that the reasonably modern (?) version of the Lance that
 > we were using (that was spec'ed long before I had anything to do with 
 > the project, not my fault) would allow multiple multicast addresses, but 
 > wouldn't allow multiple unicast addresses.  I thought that when I 
 > complained bitterly about that, my NetBSD pals laughed and suggested 
 > that most of the NICs were like that.

Yah, most NICs have a hash table to do "almost perfect" multicast
address filtering.  Some have N slots where you can put "perfect"
matches.  E.g. in the DEC Tulip, you have 16 slots, which you usually
fill like:

	Station address
	Broadcast address
	First Multicast addresss
	Last Multicast address

If you have more than 14 multicast addresses, you can then add them
to the hash table, or you can simply do all filtering (including broadcast
and unicast) via the hash table.  Mmm, flexibility :-)

        -- Jason R. Thorpe <>