Digital Tulip Design

Donald Becker
Sat Apr 29 14:01:08 2000

On Sat, 29 Apr 2000, Ed Clarke wrote:

> > The only common hardware that supports multiple station addresses is the
> > Digital Tulip design.  That feature isn't included in most of the Tulip
> > work-alikes.
> So which current production cards use this chip?  I really don't care
> what they cost; the price of twenty or so cards will disappear into the
> noise when compared to the other stuff we buy.  A good switch is a
> couple of grand, a router twenty to thirty grand.

First, to clarify: Every Ethernet card type can temporarily change its
station address to a new one.  This feature is the ability to
*simultaneously* filter-accept several unicast station addresses.

It means that you can literally do a perfect emulation of being several
machines on the LAN, not just an IP-level emulation.  Unless you are running
DECnet, you should almost never need this feature.  If you think you do, you
should probably re-think the source of your need.

The feature is closely related to the design of the excellent Tulip
multicast filter.  The Tulip has 16 addresses that it does a address match
against.  Two are taken by broadcast and the normal station address, leaving
up to 14 for matching multicast addresses.  If you have more than 14
multicast addresses you must switch to the hash-filter mode, like most other
chips.  Even there the Tulip has 512 filter bins, rather than the 64 bins of
most other chips.

> Which are the "good digital tulip" cards?  We're using a LOT of multicast.

Search for MC_HASH_ONLY in the driver.

The ASIX and ADMtek work-alikes have only 64 bit hash filters.
The 21143 and PNIC-2 have the full list + 512-bit-filter

Donald Becker
Scyld Computing Corporation
410 Severn Ave. Suite 210
Annapolis MD 21403

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