Root Port - Cisco Catalyst 2000 Configuration Handbook

128 Cisco LAN Switching Configuration Handbook
c. Follow the root port toward the root bridge.
The port is in the portfast mode
...(output removed)...
Interface Gi0/1 (port 67) in Spanning tree 534 is FORWARDING
Port path cost 3004, Port priority 128
Designated root has priority 8000, address 00d0.0457.3a15
Designated bridge has priority 32768, address 00d0.ff8a.2a15
Designated port is 7, path cost 2
Timers: message age 3, forward delay 0, hold 0
BPDU: sent 3, received 2967537
Interface Gi0/2 (port 75) in Spanning tree 534 is FORWARDING
Port path cost 4, Port priority 128
Designated root has priority 8000, address 00d0.0457.3a15
Designated bridge has priority 49152, address 0005.32f5.45ef
Designated port is 75, path cost 3006
Timers: message age 0, forward delay 0, hold 0
BPDU: sent 2967519, received 1
switch#
Remember that a switch has only one root port, and that port leads toward the
root bridge. A switch can have many designated ports, and those lead away from
the root bridge. Our goal is to find the neighboring switch that connects to the

root port.

IOS shows the root port as a logical port number (port 67). The port number is an
index into the interfaces according to the STP. You can either page through the out-
put until you find the interface with the port number, or you can use the EXEC
command show spanning-tree brief | begin VLANvlan to see only the port num-
ber associated with the specific VLAN number. An example of this follows:
switch# show spanning-tree brief | begin VLAN534
VLAN534
Spanning tree enabled protocol IEEE
ROOT ID Priority 8000
Address 00d0.0457.3a15
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec