[I figured it was more than time to change the subject on this thread. ] Ok, I see the confusion here. The backup machine generally does _not_ perform the same functions as the primary machine until a failure occurs. Then, and only then, does it start to 'talk' on the net. Again, this is not something supported by standard OS's, but rather something that requires getting down into the guts of things. In fact, the implementations I have seen of these mantain a high bandwidth link between the primary and secondary machine that is used to keep them in sync until a failure occurs. Bob Ammerman RAm Systems (contract development of high performance, high function, low-level software) ----- Original Message ----- From: Olin Lathrop To: Sent: Monday, September 04, 2000 2:40 PM Subject: Re: [pic]: lousy code protection on F87X !!! Are you kidding me? > > Normally, this is a _very_ bad idea. However, it does allow for a very > slick > > way to provide redundant hosts for a specific function (although normal > > desktop OS's don't support this concept). > > I don't think it's that easy. In theory is wouldn't matter how many MACs > grab the data for the same address, since there is no ACK for ethernet > packets. However, you get into trouble when either or both cards try to > write. This can happen even when not obvious, like in response to certain > broadcasts for example. What if someone simply did a PING to any IP address > supported by either card? I think that would result in major confusion > because sooner or later both cards wouldn't respond identically at the > identical time (well within 100nS). > > > ***************************************************************** > Olin Lathrop, embedded systems consultant in Devens Massachusetts > (978) 772-3129, olin@cognivis.com, http://www.cognivis.com > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > "[PIC]:" PIC only "[EE]:" engineering "[OT]:" off topic "[AD]:" ad's -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:" PIC only "[EE]:" engineering "[OT]:" off topic "[AD]:" ad's