System Configuration
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device (except for the root device) which incurs the lowest path
cost when forwarding a packet from that device to the root device.
Then it selects a designated bridging device from each LAN
which incurs the lowest path cost when forwarding a packet from
that LAN to the root device. All ports connected to designated
bridging devices are assigned as designated por ts. After
determining the lowest cost spanning tree, it enables all root por ts
and designated ports, and disables all other ports. Ne twork
packets are therefore only forwarded between root ports and
designated ports, eliminating any possible network l oops.
Once a stable network topology has been established, all bridges
listen for Hello BPDUs (Bridge Protocol Data Units) transmitted
from the root bridge. If a bridge does not get a Hello BPDU afte r a
predefined interval (Maximum Age), the bridge assumes that the
link to the root bridge is down. This bridge will then in itiate
negotiations with other bridges to reconfigure the network to
reestablish a valid network topology.