Description

This KB explains an interface-down scenario which happens due to a BPDU[Bridge protocol data unit] error and explains the steps to fix the same. Additionally, KB also highlights ways to find out if the end device is sending BPDU or not.

Symptoms

Interface connected to an end device will be down with no signs of Physical layer or configuration issue.

Solution

An interface configured as an edge port within RSTP/VSTP/MSTP is not expected to receive BPDU from the end device connected. It will transition itself to a non-edge port unless bpdu-block-on-edge is configured within RSTP/VSTP/MSTP.

However, a rogue end device may start sending BPDU on an edge port with bpdu-block-on-edge configured which will bring the interface down. 

To verify that the interface went down due to a BPDU error check the below Output on the EX/QFX device:-

user@device> show interfaces xe-0/0/8:0
Physical interface: xe-0/0/4:0, Enabled, Physical link is Down
 Link-level type: Ethernet, MTU: 9192, LAN-PHY mode, Speed: 10Gbps, BPDU Error: Detected

As highlighted "BPDU Error: Detected" will be seen in the output of the "show interfaces <interface name>"

To clean this error state execute the below command:-

 

user@device>clear ethernet-switching recovery-timeout interface <Interface-name>

 

This will bring up the interface on the QFX/EX device.



In a scenario where the end device sends BPDUs intermittently, the firewall filter below can be used to confirm if BPDU is being received on the end device or if the issue is on the EX/QFX side.

set firewall family ethernet-switching filter count_stp interface-specific
set firewall family ethernet-switching filter count_stp term 1 from destination-mac-address 01:80:c2:00:00:00/48
set firewall family ethernet-switching filter count_stp term 1 then accept
set firewall family ethernet-switching filter count_stp term 1 then count c1
set firewall family ethernet-switching filter count_stp term 2 then accept

If the firewall counter increments then the end device needs to be investigated but if the counter is zero then EX/QFX needs to be further investigated. Please  open a case with JTAC:-


If the scenario requires to keep some interfaces configured under the spanning tree protocol as Edge, but the configuration is not specific and all interfaces are configured as Edge as per example below, the same may cause trunk ports to go down if the other devices in the topology are running spanning tree and sending BPDUs. Assuming that all interfaces need to be participating in spanning tree but some of them are trunk, you may just delete the stanza "edge". 
set protocols rstp interface all edge
set protocols rstp bpdu-block-on-edge

Modification History

2024-03-07 : Article Created

Related Information

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/statement/edge-edit-protocols-stp.html

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/statement/edge-edit-protocols-stp.html