Incomplete MST configuration

[walfors]

Hi there,

I noticed an incomplete MST configuration when troubleshooting a client's network for packet drops:
what are the implications if the "name of the region" and the "revision number" are omitted?

The MST seems to experience topology changes so something strange is going on, but it is due to the missing parameters.

They have a core of Cisco switches (IE-5000-12S12P-10G), and none Cisco switches at the edge. 

Best ones,
L Walfors

[balaji.bandi]

Post the configuration and IOS running on the device.

also, post the output you see as a problem for us to understand correctly the issue.

#show spanning-tree mst configuration
#show spanning-tree mst

[walfors]

Hi,

spanning-tree mode mst
spanning-tree extend system-id
spanning-tree mst 0 priority 20480

The problem description was "packet drops" but it is the topology changes that caught my attention. For instance:
  #show spanning-tree vlan 1 detail
  MST0 is executing the mstp compatible Spanning Tree protocol
  <>
  Number of topology changes 112 last change occurred 1d17h ago
  from GigabitEthernet1/1

The interface in question is a "P2p Edge port" so I'm not sure about the spanning tree function:
interface GigabitEthernet1/1
 description Server
 switchport trunk allowed vlan 1
 switchport mode trunk
 spanning-tree portfast edge trunk
 spanning-tree bpdufilter enable

They use VLAN 1 as the management network. Yes, a bit odd configuration!

IOS version is 15.2(7)E3.

Thanks,
L Walfors

[MHM Cisco World]

can I see the 
show spanning tree in cisco SW?

[balaji.bandi]

The problem description was "packet drops" but it is the topology changes that caught my attention.

sure if your STP is not configured as expected and where the root bridge is, you see a lot of STP topology changes when ever there is an issue with adjacency switches and depends on your network size.

make sure you have the right device root bridge to solve this issue. (especially using vlan1 as the default vlan in Cisco device) any device added to the network claim they are root bridge (depends on the STP root election process.)

[walfors]

Thanks you for your answers!

Attached is "sh spanning-tree".
The Te1/25-27 are to other Cisco switches, the rest of the interfaces are access ports.
(and here I noticed Gi1/13 & Gi1/25 are missing the portfast command)

Thanks,
L Walfors

[MHM Cisco World]

Gi1/13              Desg FWD 20000     128.13   P2p 
Gi1/15              Desg FWD 20000     128.15   P2p 
Te1/25              Desg FWD 2000      128.29   P2p 
Te1/26              Root FWD 2000      128.30   P2p 
Te1/27              Desg FWD 2000      128.31   P2p  

which of these port connect to non-cisco SW 

[walfors]

Te1/27              Desg FWD 2000      128.31   P2p

This interface is to a non-Cisco.

[MHM Cisco World]

show spanning-tree interface Te1/27 <<- share this please

[balaji.bandi]

Thank you for sharing the config:

when you congfiguring spanning tree edge ( follow below rules)

The Te1/25-27 are to other Cisco switches, the rest of the interfaces are access ports.
(and here I noticed Gi1/13 & Gi1/25 are missing the portfast command)

• portfast edge is used to configure a port on which an end device is connected, such as a PC. All ports directly connected to end devices cannot create bridging loops in the network. Therefore, the edge port directly transitions to the forwarding state, and skips the listening and learning stages. However, the specific command configures a port such that if it receives a BPDU, it immediately loses its edge port status and becomes a normal spanning-tree port.
• You use the portfast network on trunk ports to enable bridge assurance feature which protects against loops by detecting unidirectional links in the STP topology. But normally bridge assurance is enabled by default.
• A spanning tree normal port is one that functions in the default manner for spanning tree. Under normal circumstances it will transition from the Listening, Learning, Forwarding stages based on the default timers.

This switch is not root bridge - how is your network looks like any diagram ?

Do you have Loops in the network ?  ( as per output does not show any block ?)

[walfors]

Hi guys,

I went thru all the ports, and added some missing "portfast edge".
I also found a "P2p Bound (RSTP)" to one of the non-Cisco switches: MST was not activated on that port of the non-Cisco, which of course was a major mistake.

The network has become stable now.

Thanks for the assistance,
L Walfors