show span

Displays the Spanning Tree Protocol (STP) information for the device.
Syntax
show span [ number |designated-protect | fast-uplink-span | pvst-mode | root-protect ]
show span [ detail [ number | vlan vlan-id [ ethernet stackid/slot/port | lag lag-id ] ] ]
show span [ vlan vlan-id [ethernet stackid/slot/port | fast-uplink-span |lag lag-id ] ]
Parameters
number
Displays only the entries after the specified number.
designated-protect
Displays the designated forwarding state disabled.
fast-uplink-span
Displays the status of ports with Fast Uplink Span enabled.
pvst-mode
Displays STP information for the device Per VLAN Spanning Tree Plus (PVST+) compatibility configuration.
root-protect
Displays the STP root guard state.
detail
Displays the detailed STP information for a port.
vlan vlan-id
Displays the STP information for a VLAN.
ethernet stackid/slot/port
Displays STP information for an Ethernet port.
lag lag-id
Displays STP information for a LAG virtual interface.
Modes

User EXEC mode

The show span command displays the following information:

Output field Description
VLAN ID The port-based VLAN that contains this spanning tree (instance of STP). VLAN 1 is the default VLAN. If you have not configured port-based VLANs on this device, all STP information is for VLAN 1.
Root ID The ID assigned by STP to the root bridge for this spanning tree.
Root Cost The cumulative cost from this bridge to the root bridge. If this device is the root bridge, the root cost is 0.
Root Port The port on this device that connects to the root bridge. If this device is the root bridge, the value is "Root" instead of a port number.
Priority Hex This device or VLAN STP priority. The value is shown in hexadecimal format.
Max age sec The number of seconds this device or VLAN waits for a configuration BPDU from the root bridge before deciding the root has become unavailable and performing a reconvergence.
Hello sec The interval between each configuration BPDU sent by the root bridge.
Hold sec The minimum number of seconds that must elapse between transmissions of consecutive Configuration BPDUs on a port.
Fwd dly sec The number of seconds this device or VLAN waits following a topology change and consequent reconvergence.
Last Chang sec The number of seconds since the last time a topology change occurred.
Chg cnt The number of times the topology has changed since this device was reloaded.
Bridge Address The STP address of this device or VLAN.
Port Num The port number.
Priority Hex The port STP priority, in hexadecimal format.
Path Cost The port STP path cost.
State The port STP state. The state can be one of the following:
  • BLOCKING: STP has blocked Layer 2 traffic on this port to prevent a loop. The device or VLAN can reach the root bridge using another port, the state of which is FORWARDING. When a port is in this state, the port does not transmit or receive user frames, but the port does continue to receive STP BPDUs.
  • DISABLED: The port is not participating in STP. This can occur when the port is disconnected or STP is disabled on the port.
  • FORWARDING: STP is allowing the port to send and receive frames.
  • LISTENING: STP is responding to a topology change and this port is listening for a BPDU from neighboring bridges in order to determine the new topology. No user frames are transmitted or received during this state.
  • LEARNING: The port has passed through the LISTENING state and will change to the FORWARDING state depending on the results of STP reconvergence. The port does not transmit or receive user frames during this state. However, the device can learn the MAC addresses of frames that the port receives during this state and make corresponding entries in the MAC table.
  • DESIGNATED INCONSISTENT: (Shows as DESI-INCONS in the output.) You can disallow the designated forwarding state on a port in STP 802.1D or 802.1W with the spanning-tree designated-protect command. If STP tries to put this port into the designated forwarding role, the device puts this port into a designated inconsistent STP state. This is effectively equivalent to the listening state in STP in which a port cannot transfer any user traffic. When STP no longer marks this port as a designated port, the device automatically removes the port from the designated inconsistent state.
Fwd Trans The number of times STP has changed the state of this port between BLOCKING and FORWARDING.
Design Cost The cost to the root bridge as advertised by the designated bridge that is connected to this port. If the designated bridge is the root bridge itself, the cost is 0. The identity of the designated bridge is shown in the Designated Bridge field.
Designated Root The root bridge as recognized on this port. The value is the same as the root bridge ID listed in the Root ID field.
Designated Bridge The designated bridge to which this port is connected. The designated bridge is the device that connects the network segment on the port to the root bridge.

The show span detail command displays the following information:

Output field Description
Active Spanning Tree protocol The VLAN that contains the listed ports and the active Spanning Tree Protocol. The STP type can be one of the following:
  • MULTIPLE SPANNNG TREE (MSTP)
  • GLOBAL SINGLE SPANNING TREE (SSTP)
Bridge identifier The STP identity of this device.
Active global timers The global STP timers that are currently active, and their current values. The following timers can be listed:
  • Hello: The interval between Hello packets. This timer applies only to the root bridge.
  • Topology Change (TC): The amount of time during which the topology change flag in Hello packets will be marked, indicating a topology change. This timer applies only to the root bridge.
  • Topology Change Notification (TCN): The interval between Topology Change Notification packets sent by a non-root bridge toward the root bridge. This timer applies only to non-root bridges.
Active Timers The current values for the following timers, if active:
  • Message age: The number of seconds this port has been waiting for a Hello message from the root bridge.
  • Forward delay: The number of seconds that have passed since the last topology change and consequent reconvergence.
  • Hold time: The number of seconds that have elapsed since transmission of the last Configuration BPDU.
BPDUs Sent and Received The number of BPDUs sent and received on this port since the software was reloaded.
Examples

The following example shows the STP information. 

device# show span
VLAN 1 BPDU cam_index is 3 and the Master DMA Are(HEX)
STP instance owned by VLAN 1
Global STP (IEEE 802.1D) Parameters:
VLAN      Root              Root    Root    Prio    Max    He-    Ho-    Fwd     Last     Chg  Bridge
ID        ID                Cost    Port    rity    Age    llo    ld     dly     Chang    cnt  Address
                                            Hex     sec    sec    sec    sec     sec
1         800000e0804d4a00  0        Root    8000   20     2      1      15       689      1   00e0804d4a00
Port STP Parameters:
Port         Prio     Path     State        Fwd     Design    Designated        Designated
Num          rity     Cost                  Trans   Cost      Root              Bridge
             Hex
1            80       19       FORWARDING   1       0         800000e0804d4a00  800000e0804d4a00
2            80       0        DISABLED     0       0         0000000000000000  0000000000000000
3            80       0        DISABLED     0       0         0000000000000000  0000000000000000
4            80       0        DISABLED     0       0         0000000000000000  0000000000000000
5            80       19       FORWARDING   1       0         800000e0804d4a00  800000e0804d4a00
6            80       19       BLOCKING     0       0         800000e0804d4a00  800000e0804d4a00
7            80       0        DISABLED     0       0         0000000000000000  0000000000000000
<lines for remaining ports excluded for brevity>

The following example shows the detailed STP information. 

device# show span detail
======================================================================
VLAN 1 - SPANNING TREE (IEEE 802.1D) ACTIVE
======================================================================
Bridge identifier    - 0x800000a0c9c002a0
Active global timers - Hello: 0 
Topology change not set, Topology change detected not set, Topology change time 35
Number of topology changes: 113
Last topology change occured 46 second(s)  ago on lg40


Port 1/1/1 is FORWARDING
  Port - Path cost: 4, Priority: 128, Port Identifier:128.0, Root: 0x800000a0c9c002a0 Root Bridge Priority:32768
  Designated - Bridge: 0x800000a0c9c002a0, Priority:32768, Interface: 0, Identifier:128.0, Path cost: 0 
  Active Timers - Hold: 0
  BPDUs - Sent: 5968, Received: 0
Port 1/1/2 is DISABLED
Port 1/1/3 is DISABLED
Port 1/1/4 is FORWARDING
  Port - Path cost: 4, Priority: 128, Port Identifier:128.3101, Root: 0x800000a0c9c002a0 Root Bridge Priority:32768
  Designated - Bridge: 0x800000a0c9c002a0, Priority:32768, Interface: 3101, Identifier:128.3101, Path cost: 0 
  Active Timers - Hold: 0
  BPDUs - Sent: 5978, Received: 52

The following example displays STP information for an individual port in a specified VLAN. 

device# show span detail vlan 1 ethernet 1/1/1
======================================================================
VLAN 1 - SPANNING TREE (IEEE 802.1D) ACTIVE
======================================================================
Bridge identifier    - 0x800000a0c9c002a0
Active global timers - Hello: 0 
Topology change not set, Topology change detected not set, Topology change time 35
Number of topology changes: 113
Last topology change occured 6 minute(s) 57 second(s)  ago on lg40


Port 1/1/1 is FORWARDING
  Port - Path cost: 4, Priority: 128, Port Identifier:128.0, Root: 0x800000a0c9c002a0 Root Bridge Priority:32768
  Designated - Bridge: 0x800000a0c9c002a0, Priority:32768, Interface: 0, Identifier:128.0, Path cost: 0 
  Active Timers - None
  BPDUs - Sent: 6152, Received: 0

The following example displays STP information in a VLAN. 

device# show span vlan 100
STP instance owned by VLAN 100 

Global STP (IEEE 802.1D) Parameters: 

VLAN Root             Root Root      Prio Max He- Ho- Fwd Last    Chg Bridge 
 ID   ID              Cost Port      rity Age llo ld  dly Chang   cnt Address 

                                     Hex  sec sec sec sec sec 
 100 8000cc4e24b46fcc 0    Root      8000 20  2   1   15  11      1   cc4e24b46fcc 

Port STP Parameters: 

Port      Prio Path  State       Fwd    Design  Designated       Designated 
Num       rity Cost              Trans  Cost    Root             Bridge 
          Hex 
1/1/1     80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc 

1/1/2     80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc 
1/1/3     80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc 

1/1/4     80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc 

1/1/5     80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc 

1/1/6     80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc 

1/1/7     80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc 

1/1/8     80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc 

lg1       80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc 

lg256     80   4     FORWARDING  1      0       8000cc4e24b46fcc 8000cc4e24b46fcc

The following example shows the port path costs after the 802.1D 2004 path cost method is globally configured. The Ethernet 1/1/5 and 1/1/6 port speeds are 1 Gbps. 

device# show span vlan 100

STP instance owned by VLAN 100

Global STP (IEEE 802.1D) Parameters:

VLAN Root             Root Root      Prio Max He- Ho- Fwd Last    Chg Bridge      
 ID   ID              Cost Port      rity Age llo ld  dly Chang   cnt Address     
                                     Hex  sec sec sec sec sec                     
 100 8000cc4e246eb200 0    Root      8000 20  2   1   15  12739   2   cc4e246eb200

Port STP Parameters:

Port      Prio Path      State       Fwd    Design  Designated       Designated       
Num       rity Cost                  Trans  Cost    Root             Bridge           
          Hex                                                                         
1/1/5     80   20000     FORWARDING  1      0       8000cc4e246eb200 8000cc4e246eb200 
1/1/6     80   20000     FORWARDING  1      0       8000cc4e246eb200 8000cc4e246eb200
History
Release version Command history
08.0.61 This command was modified to add the lag lag-id parameter.
08.0.70 This command was modified to display path cost values from the IEEE 802.1D 2004 standards.
10.0.00 This command was modified to display more topology information details.
Parent topic: Show Commands