With these
changes, that brain dead bridge is recognized and avoided by its neighbors. The system
administrator can, therefore, quickly find the problem and fix it.
This change has been implemented by some vendors and will become part of IEEE
Std 802.1aq. With this change, the chance of permanent forwarding loops is no greater
for bridged networks than for routed networks. The cost of this solution is that the
required configuration makes the bridges no longer ???plug and play.??? This, of course, is
not a problem for Carrier Ethernet provider networks.
Flooded Unicast Frames When a frame is received by a bridge that has a destination MAC
address that is not known to that bridge, the bridge floods the frame on all ports on which
that frame??™s VLAN is enabled. The frame may be eventually flooded on all the ports in the
network configured for that VLAN, presumably meaning all the ports belonging to that
particular customer. This is often perceived as a flaw in bridged networks.
Let??™s look at the problem more closely. First, only one customer is affected by this
flood??”the customer on whose VLAN the frame is being carried. The frame cannot be
flooded to any port not associated with that one VLAN and that one customer.
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