At 08:37 AM 6/18/02, Tim Potier wrote: > > Unicast means a specific address. The first bit of the > > destination MAC > > address (which is the first bit transmitted) is a zero. > > > >In terms of the definitions, I was reading through the Perlman book and >noted question of the "necessity to distinguish between multicast and >broadcast". I agree that the terms a concretely defined, but whether Cisco >subscribes to those definitions might be in question
The terms are well defined and Cisco uses them correctly in the documents I have seen. Perlman doesn't argue with the definitions, but she does make the point that broadcasts are kind of silly since they go to every station regardless of the protocols running on that station. The station takes in the broadcast and looks at the EtherType or SAP to see if the frame really needs to be accepted. If the sender had used a protocol-specific multicast, then this could be avoided. Since there are no protocols in existence that really need to go to all stations, broadcasts are theoretically not necessary. BPDUs can just go to bridges and switches. CDP can go to just Cisco devices. NetBIOS could just go to NetBIOS stations. ARP could go to just IP stations, etc. She also has an interesting discussion on why it's necessary to identify multicast addresses. She says that theoretically it's not necessary to reserve a bit in the address to differentiate group and individual addresses. Ideally, the software would tell the chip all the different addresses to listen for. But what would be the max number of these? The chips are designed such that they look for a set of multicasts, but they may actually receive more than the applications registered for. But note that she isn't discussing the terminology. She's discussing protocol and chip implementations. That's somewhat valuable to this group, whereas arguing about fundamental concepts is not. ;-) Some stuff is black and white. Priscilla >Thanks again... your info certainly cleared this mess up. ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=46912&t=46839 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
