mas@bridge2.ESD.3Com.COM (Mike Smith) (11/11/89)
In article <12710002@hpspdra.HP.COM> jpeck@hpspdra.HP.COM (Joe Peck) writes: >> The Sniffer comes with a file of many > >Anytime the first byte of the Ethernet address is odd, the multicast bit >is set. This allows more than on node to receive the packet, provided >they're set up to accept it. . . . > >Joe Peck For multi-destination addresses, the least significant bit (LSB) of the first byte of the six byte address indicates the address as a group address. This is this first bit of the address that comes down the wire. If the next bit (U-bit) is set, it is a globally administered address. If all 48 bits are set, it is a broadcast address. Broadcast is the only type of group address that is specifically defined at the 802.3 MAC layer. All other types of group addresses are called multicast and are defined by higher layers of the various protocol stacks (IDP, IP, LLC, et RP, ARP, LLC, etc). Every station has to be able to recognize at least the broadcast type of address. I don't know where global address administration is defined.
pat@hprnd.HP.COM (Pat Thaler) (11/14/89)
> / hprnd:comp.dcom.lans / mas@bridge2.ESD.3Com.COM (Mike Smith) / 11:36 am Nov 10, 1989 / > In article <12710002@hpspdra.HP.COM> jpeck@hpspdra.HP.COM (Joe Peck) writes: > >> The Sniffer comes with a file of many > > > >Anytime the first byte of the Ethernet address is odd, the multicast bit > >is set. This allows more than on node to receive the packet, provided > >they're set up to accept it. . . . > > > >Joe Peck > > For multi-destination addresses, the least significant bit (LSB) of the first > byte of the six byte address indicates the address as a group address. > This is this first bit of the address that comes down the wire. If > the next bit (U-bit) is set, it is a globally administered address. If > all 48 bits are set, it is a broadcast address. Broadcast is the only type of > group address that is specifically defined at the 802.3 MAC layer. All other > types of group addresses are called multicast and are defined by higher > layers of the various protocol stacks (IDP, IP, LLC, et RP, ARP, LLC, etc). > > Every station has to be able to recognize at least the broadcast type of > address. I don't know where global address administration is defined. > ---------- You will find the use of the individual/group bit (group = multicast) and the universal/local bit (universal = global) defined in 3.2.3.1 of the IEEE 802.3 standard. It is also covered in 802.2 LLC. Xerox administered global addresses in the past. They have since turned administration over to IEEE. Pat Thaler