Specifications

Ethernet Data Frames 4-11
Ethernet Data Frames
The 00-00-1D manufacturer ID belongs to Cabletron Systems. When a
specific Ethernet address is used as the destination address in a packet,
that packet will be decoded only by the station with that specific address.
Multicast Addressing
At times it is necessary to communicate with many devices on a network
simultaneously. For instance, a network management station might poll or
query a group of devices to determine their status. Instead of keeping a list
or table of unique addresses a group address can be used. This type of
group addressing is accomplished using a multicast address.
A multicast address is formed by modifying the manufacturer ID portion
of the destination address. As shown in Figure 4-5, the least significant bit
of the first byte is changed from a 0 to a 1. The net result is to turn a
Cabletron Systems address of 00-00-1D... into a multicast address of
01-00-1D... A multicast address is destined for devices from a particular
manufacturer.
Figure 4-5. Ethernet Multicast Address
Broadcast Addressing
A broadcast address is an address that is meant to be heard by all stations
on the network. Certain protocols running on workstations will
occasionally send out broadcast messages to servers on the network to let
the servers know that the node is on-line.
00-00-1D-00-26-A3
01-00-1D-00-26-A3
Address
Multicast Address
0000 0000
0000 0001
Lowest bit of the first byte
changes from 0 to 1
1913-09