When the PortFast feature is enabled, the port
changes from a blocking state to a forwarding state
without making the intermediate spanning-tree state
changes.
Switch#show running-con?¬?g
interface type slot/port
Indicates whether PortFast has been con?¬?gured on a port.
It can also be used to show if con?¬?guration has occurred
on an EtherChannel link by specifying port-channel
channel_number in place of type slot/port.
100Base-T
10Base-T
Root Bridge
Default Priority 32768
MAC 0c00.1111.0000
Port 1 Port 1
Port 0
Default Priority 32768
MAC 0c00.1111.2222
Default Priority 32768
MAC 0c00.1111.1111
Port 0
Switch Z
Switch X Switch Y
Port 1 Port 0
Improving Performance with Spanning Tree 55
The following describes the STP port states illustrated in Figure 2-26:
?– The root bridge is switch Z, which has the lowest BID.
?– The root port is port 0 on switches X and Y. Port 0 is the lowest-cost path to the root
on both switches.
?– The designated ports on switch Z are port 0 and port 1. All ports on the root are
designated ports. Port 1 of switch X is a designated port for the segment between
switch X and switch Y. Because switch X and switch Y have the same path cost to the
root bridge, the designated port is selected to be on switch X because it has a lower BID
than switch Y.
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