asked on Meaning of Port number in Show spanning Tree
Meaning of Port number in Show spanning Tree
in the output of the command below I see:
Port 1 (Ethernet0/0)
I wonder what Port 1 means? I thought the port is the same as interface.
Thank you
in the output of the command below I see:
Port 1 (Ethernet0/0)
I wonder what Port 1 means? I thought the port is the same as interface.
Thank you
SW1#sh spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol ieee
Root ID Priority 24596
Address aabb.cc00.0400
Cost 200
Port 1 (Ethernet0/0)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32788 (priority 32768 sys-id-ext 20)
Address aabb.cc00.0100
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Et0/0 Root FWD 100 128.1 Shr
Et0/1 Altn BLK 100 128.2 Shr
SW1#
Networking ProtocolsSwitches / HubsNetwork Architecture
Last Comment
jskfan
Port <number> is part of switch internal port numeration on device that is needed to establish STP port identifier. Physical port numeration does not need to match exact physical port number (and sometimes even can't match since device can have more than one line card). Typically, physical port count starts with 1 and each next port increases by 1, but it may depend on hardware model and line card that is in use.
In the case above port eth0/0 is port 1 and eth0/1 is port 2. If you want to check each port number on device you can do it by issuing command show spanning-tree detail. Port number in example above is showing which port is chosen to be STP root port on local device.
Port priority (default value is 128) and port number together make port identifier (the same way as STP priority and MAC address create STP bridge ID). Port identifier is last option that can/will be used in determination of port which will be unblocked, if all other previous steps in STP election fail to determine best path to root bridge (example would be 2 switches connected to each other with two or more links - port identifier is option of last resort that can be used to determine which port should be elected as root port (will be in forwarding state) on device which lost STP root bridge election).
In the case above port eth0/0 is port 1 and eth0/1 is port 2. If you want to check each port number on device you can do it by issuing command show spanning-tree detail. Port number in example above is showing which port is chosen to be STP root port on local device.
Port priority (default value is 128) and port number together make port identifier (the same way as STP priority and MAC address create STP bridge ID). Port identifier is last option that can/will be used in determination of port which will be unblocked, if all other previous steps in STP election fail to determine best path to root bridge (example would be 2 switches connected to each other with two or more links - port identifier is option of last resort that can be used to determine which port should be elected as root port (will be in forwarding state) on device which lost STP root bridge election).
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Thank you Guys
https://www.cisco.com/c/m/en_us/techdoc/dc/reference/cli/nxos/commands/l2/show-spanning-tree.html