These addresses are of the form, 01-80-C0-00-00-0x
(hexadecimal), where the last 4 bits (x) range from 0 through F. A non-VLAN bridge
never forwards a frame from one port to another if it has one of these addresses as its
destination. Stations should never use these addresses, except when running protocols
defined to use these addresses, generally between the station and the nearest bridge.
Bridging versus Routing
Bridging has been presented so far as a natural progression based on the characteristics
of the original Ethernet media and the need for plug-and-play interoperability. It is
now time to step back and see what the essential differences are between bridges and
routers, which are a somewhat more familiar technology to many readers.
The essential characteristics of a bridged LAN and some of the differences between
bridged networks and routed networks include the following:
?– Bridges operate on 48-bit Ethernet MAC addresses, not 32- or 128-bit IP addresses.
MAC addresses are, in essence, globally unique manufacturers??™ serial numbers.
Unlike IP addresses, MAC addresses convey no information about where a device
is located.
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