Subject: Re: bpf write() to local host
To: Curt Sampson <>
From: David Laight <>
List: tech-net
Date: 01/23/2003 12:08:57
> > Adding an alias really requires that the ethernet hardare support
> > multiple MAC addresses, some modern ones do.
> All that I have ever seen do. You have to have this to support multicast.

No you don't...
Multicast is often supported by hashing [1] received multicast mac address
and looking up in a 64 bit table.
Most chipsets also have a 'promiscuous for multicasts' bit - when they
will receive all multicasts and packets for the stations own mac address.

Full promiscuous and software filtering can stop an otherwise
working card being able to do anything useful.  It is a bad, bad idea.
(unless your want to sniff the network...)


[1] usually 6 bits of the crc register after the MAC address has
been processed.

David Laight: