Support Support Downloads Knowledge Base Service Request Manager My Juniper Community

Knowledge Base

Search our Knowledge Base sites to find answers to your questions.

Ask All Knowledge Base Sites All Knowledge Base Sites JunosE Defect (KA)Knowledge BaseSecurity AdvisoriesTechnical BulletinsTechnotes Sign in to display secure content and recently viewed articles

Resolution Guide - EX - Troubleshoot Spanning Tree Protocol (STP)

0

0

Article ID: KB22774 KB Last Updated: 05 Mar 2017Version: 3.0
Summary:

This article will assist with Spanning Tree Protocol (STP) troubleshooting in a step-by-step approach with EX Series Ethernet switches configured as a Layer 2 switch.

Spanning Tree Protocol was introduced as 802.1D to have a loop-free network.


Symptoms:

Symptoms:

  • Loop has been formed in the network
  • Topology changes have increased
  • Layer 2 traffic is disrupted
  • Interface goes into BLOCK state causing traffic to be dropped
  • Traffic is flooding

Cause:

Solution:

Perform the following steps to troubleshoot:


[Map out network topology]

Step 1. Map out the network topology and identify the following components.   For an example topology with definitions, refer to KB22832 - Example Spanning Tree Network Topology with EX switches.



[Spanning-Tree Protocol Flavor Check]

Step 2.  Verify that all the switches connected in the network are running the same Spanning-Tree Protocol flavor (i.e RSTP, MSTP, STP, or VSTP).

To do this, run the command:   show spanning-tree bridge
The Spanning-Tree Protocol favor can be found under the 'Enabled protocol'. For more information, refer to KB22775 - Confirm the flavor of the Spanning Tree Protocol (STP) running on the switch.

Are all the switches connected in the network running the same Spanning-Tree Protocol flavor?



[Root Bridge Interface Check]

Step 3.  Starting on the Root Bridge in your network, are all the interfaces on this Root switch in the Forwarding (FWD) state?

To verify, run the command:   show spanning-tree interface
In STP, all connected ports on a Root Bridge should be in FWD state.
For more information on the output of the above command, refer to http://www.juniper.net/techpubs/en_US/junos11.4/topics/reference/command-summary/show-spanning-tree-interface-spanning-trees-ex-series.html

  • Yes - Continue to Step 4
  • No - Call your technical support representative.  This is a basic requirement.


[Topology Change Check] 

Step 4.  On this switch, do you see the 'Number of topology changes' increasing?

To verify, run the command:   show spanning-tree bridge detail
When the 'Number of topology changes' increases, it typically means that the physical state of a port on the switch is changed (like a non-edge port coming up). For more information, refer to KB22776 - Identify if a topology change has taken place in a Spanning-Tree network.

  • Yes - Continue to Step 5
  • No - Jump to Step 7 (to do Basic Loop Check)


Step 5.  On this switch, verify if the non-edge interfaces have changed state. 

Run the following commands and analyze the output to verify if an interface has changed state. For a definition of non-edge interface and how to tell if an interface has flapped, refer to KB22803 - Identify an interface that has flapped on an EX series switch.

show log messages
show interfaces <interface-name> extensive

Do you see that a non-edge interface has changed state?

  • No - Continue to Step 6
  • Yes - Troubleshoot the interface that has flapped, and the STP should stablize:
    • Check for any loose cables.
    • Check for any outage.
    • Check if any configuration change has been made.



Step 6.  Since the cause of the topology change was not identified in Step 5 on the current switch, we need to move to the next node in the Spanning Tree to trace the source of the topology change.

The next node in the Spanning Tree can be determined from the value of the 'Topology change Initiator' field; it is the node from which the current switch received the topology change. 

Run the command:   show spanning-tree bridge detail

Switch@juniper>show spanning-tree bridge

STP bridge parameters
Context ID : 0
Enabled protocol : RSTP <--
Root ID : 32768.28:c0:da:3d:50:40
Hello time : 2 seconds
Maximum age : 20 seconds
Forward delay : 15 seconds
Message age : 0
Number of topology changes : 2
Time since last topology change : 3218 seconds 
Topology change initiator : ge-0/0/4.0   <-------------
Topology change last recvd. from : 2c:6b:f5:8b:23:04
Local parameters
Bridge ID : 32768.28:c0:da:3d:50:40
Extended system ID : 0
Internal instance ID : 0

a.  Connect to the switch off of the interface identified in the 'Topology Change initiator' output. 

b.  Go to
Step 4 and repeat Steps 4-5 (Repeat Steps 4-5 on the switch from which the topology change is received.)        



[Basic Loop Check]

Step 7.  Analyze the traffic interface activity for unusually heavy traffic.

To do this, run the following command, and compare the output with the baseline output when traffic is normal.

SwitchA> monitor interface traffic

For example, below is the output of SwitchA with normal network activity:
Interface    Link  Input packets        (pps)     Output packets        (pps)
 ge-0/0/0    Down              0          (0)                0          (0)
 ge-0/0/1    Down              0          (0)                0          (0)
 ge-0/0/2    Down              0          (0)                0          (0)
 ge-0/0/3    Down              0          (0)                0          (0)
 ge-0/0/4    Down              0          (0)                0          (0)
 ge-0/0/5    Down              0          (0)                0          (0)
 ge-0/0/6    Down              0          (0)                0          (0)
 ge-0/0/7    Down              0          (0)                0          (0)
 ge-0/0/8    Down              0          (0)                0          (0)
 ge-0/0/9    Down              0          (0)                0          (0)
 ge-0/0/10     Up             37          (0)             5570          (0)
 ge-0/0/11   Down              0          (0)                0          (0)
 ge-0/0/12   Down              0          (0)                0          (0)
 ge-0/0/13   Down              0          (0)                0          (0)
 ge-0/0/14   Down              0          (0)                0          (0)
 ge-0/0/15   Down              0          (0)                0          (0)
 ge-0/0/16   Down              0          (0)                0          (0)
 ge-0/0/17   Down              0          (0)                0          (0)
 ge-0/0/18   Down              0          (0)                0          (0)
 ge-0/0/19   Down              0          (0)                0          (0)
 ge-0/0/20     Up             88          (0)             1646          (0)
 ge-0/0/21   Down              0          (0)                0          (0)
 ge-0/0/22   Down              0          (0)                0          (0)
 ge-0/0/23     Up            122          (0)             1639          (0)
 vcp-0       Down              0                             0
 vcp-1       Down              0                             0
 ae0           Up            125          (0)             7216          (0)
 ae1         Down              0          (0)                0          (0)
 ae2         Down              0          (0)                0          (0)
 ae3         Down              0          (0)                0          (0)
 ae4         Down              0          (0)                0          (0)
 ae5         Down              0          (0)                0          (0)

Bytes=b, Clear=c, Delta=d, Packets=p, Quit=q or ESC, Rate=r, Up=^U, Down=^D

Below is the example output of SwitchA when it is experiencing abnormal activity:  

(Note:  The packet rates below may be normal for another switch.  The key is to create a baseline and capture the packet rates during normal periods, so you can compare packet rates when experiencing problems.)

Interface    Link  Input packets        (pps)     Output packets        (pps)
 ge-0/0/0    Down              0          (0)                0          (0)
 ge-0/0/1    Down              0          (0)                0          (0)
 ge-0/0/2    Down              0          (0)                0          (0)
 ge-0/0/3    Down              0          (0)                0          (0)
 ge-0/0/4    Down              0          (0)                0          (0)
 ge-0/0/5    Down              0          (0)                0          (0)
 ge-0/0/6    Down              0          (0)                0          (0)
 ge-0/0/7    Down              0          (0)                0          (0)
 ge-0/0/8    Down              0          (0)                0          (0)
 ge-0/0/9    Down              0          (0)                0          (0)
 ge-0/0/10     Up             37          (0)             5593          (1)
 ge-0/0/11   Down              0          (0)                0          (0)
 ge-0/0/12   Down              0          (0)                0          (0)
 ge-0/0/13   Down              0          (0)                0          (0)
 ge-0/0/14   Down              0          (0)                0          (0)
 ge-0/0/15   Down              0          (0)                0          (0)
 ge-0/0/16   Down              0          (0)                0          (0)
 ge-0/0/17   Down              0          (0)                0          (0)
 ge-0/0/18   Down              0          (0)                0          (0)
 ge-0/0/19   Down              0          (0)                0          (0)
 ge-0/0/20     Up             88          (0)         35162079    (1116047)
 ge-0/0/21   Down              0          (0)                0          (0)
 ge-0/0/22   Down              0          (0)                0          (0)
 ge-0/0/23     Up       35160729    (1116048)             1640          (0)
 vcp-0       Down              0                             0
 vcp-1       Down              0                             0
 ae0           Up            125          (0)         35167672    (1116048)
 ae1         Down              0          (0)                0          (0)
 ae2         Down              0          (0)                0          (0)
 ae3         Down              0          (0)                0          (0)
 ae4         Down              0          (0)                0          (0)
 ae5         Down              0          (0)                0          (0)

Bytes=b, Clear=c, Delta=d, Packets=p, Quit=q or ESC, Rate=r, Up=^U, Down=^D

Is this switch encountering unusually heavy traffic activity on the interfaces?

  • Yes - Continue to Step 8
  • No - End of workflow.  The basic STP checks (a Topology Change Check and a Basic Loop Check) are good.  If you are still encountering a Spanning Tree Protocol issue, jump to Step 9


Step 8.   Is Spanning-Tree Protocol enabled?   For more information on how to check, refer to KB22775 - Confirm the flavor of the Spanning Tree Protocol (STP) running on the switch.

  • No - Enabling Spanning-Tree Protocol will mitigate loops, so if possible, enable Spanning-Tree Protocol on the devices in the network segment where the loop is observed.  For more information on how to do this, refer to KB22775 - Confirm the flavor of the Spanning Tree Protocol (STP) running on the switch.
  • Yes - Run the following commands to help troubleshoot this switch around the abnormal traffic flow.   If the cause cannot be identified, continue to Step 9.

  • show system processes
    show interfaces <interface-name> extensive
    show log messages


[Data Collection for further troubleshooting]

Step 9.  If the above steps do not resolve the problem, then collect the following information and open a case with your technical support representative:

  • Network Topology/Diagram labeling spanning-tree roles of each device

  • Collect the logs on the EX device:

  • show spanning-tree bridge
    show spanning-tree bridge detail
    show spanning-tree interface
    show spanning-tree interface detail
    show spanning-tree statistics interface <int>
    show spanning-tree statistics interface <int> detail

    show ethernet-switching interfaces
    show ethernet-switching table

    show interface
    show interface extensive

    show log messages

  • Request Support Information:

  • request support information all-member | no-more


Comment on this article > Affected Products Browse the Knowledge Base for more articles related to these product categories. Select a category to begin.

Security Alerts and Vulnerabilities

Security Alerts and Vulnerabilities Product Alerts and Software Release Notices Problem Report (PR) Search Tool EOL Notices and Bulletins JTAC User Guide Customer Care User Guide Pathfinder SRX High Availability Configurator SRX VPN Configurator Training Courses and Videos End User Licence Agreement Global Search