This is an arp table entry remembering.  5 min timeout is typical.
(their side, not yours).

Two options, don't change computers attached directly or
get a little appliance router thingy.  Basically, keep
one box attached to the cable bridge.

Quoting Nathan de Klepper (nathandeklepper@optushome.com.au):
> No, a cable modem of mine seems to be remembering MAC address's or something
> odd.
> Switching machines works when you leave the modem off for a while, but not
> if you switch it off for only a minute or so.
> Its for an Axil 320 (a sun clone).
> 
> ----- Original Message -----
> From: "David Laight" <david@l8s.co.uk>
> To: "Chuck Yerkes" <chuck+nbsd@snew.com>
> Cc: "Nathan de Klepper" <nathandeklepper@optushome.com.au>;
> <netbsd-users@netbsd.org>
> Sent: Tuesday, July 30, 2002 5:51 AM
> Subject: Re: manually setting MAC address
> 
> 
> > >
> > > What is it you are after?  Why would you need to change MAC addresses?
> > > (the ONLY time I've ever needed it was with an HA/Failover situation).
> >
> > In order to run decnet???
> > Requires locally administered addresses.  IIRC top 14 bits (after
> > multicast/unicast and locally/globally administerd) are the network
> > and bottom 32 the machine number.
> >
> > David
> >
> > --
> > David Laight: david@l8s.co.uk