spanning tree error ??

Unanswered Question
Sep 6th, 2010

i m getting the following error message from my core switch, c3560G.

what could be the reason ??

no changes were done on the switch these few days.

the error pop out suddenly this morning on my syslog server

X-Mailer: Cisco Network Assistant System Messages Notification Mailer

Device: BRCORE02-32nd-3560G
7w1d: %SPANTREE-2-UNBLOCK_CONSIST_PORT: Unblocking GigabitEthernet0/42 on VLAN0001. Port consistency restored.



 

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Giuseppe Larosa Mon, 09/06/2010 - 02:04

Hello Yeow,

this messages tells you that STP has re-enabled a port gi0/42 for Vlan 1. The port had been put in an inconsistency state by an STP protection mechanism like root guard or loop guard.

STP has automatically recovered from the problem.

without the protection  mechanism the port could have progressed to forwarding state or to consider itself as designated port on segment for example for having missed 3 STP BPDUs in a row that should be received by intended designated port.

If this is the first occurrency of this event I would suggest no action.

If the event happens many times you may need to investigate further.

By experience, I recommend to avoid to shut the port: let STP to handle the event or when re-enabling the port you can face a worse issue. (we had a bridging loop)

In our case, we had a trouble on 10GE link and we solved with an IOS upgrade on the C6500 side. For us it was the C4500 side that was showing events like this. The problem was that WS-6708 8 tengiga port was not correctly supported in 12.2(18)SXF and after moving to 12.2(33)SXH2 we solved.

Hope to help

Giuseppe

yeow_km Mon, 09/06/2010 - 05:14

this particular port is connected to another core switch.eg. core switch 01 to core switch 02.

this error start coming up this morning non stop.

r u saying that i should just shutdown this interface ??

both switch are WS-C3560G-48TS using IOS 12.2(35)SE5  and WS-C3560G-48PS using 12.2(53)SE.

Jon Marshall Mon, 09/06/2010 - 05:16

Perhaps you could post a few more details ie.

1) configuration on the ports on both switches for this interconnection

2) details of any other interconnections between these 2 switches

Jon

yeow_km Mon, 09/06/2010 - 05:48

interface GigabitEthernet0/41
description Uplink to BRCOR02-32ND-C3560G Gi0/42
switchport trunk encapsulation dot1q
switchport trunk native vlan 3
switchport trunk allowed vlan 1-7
switchport mode trunk

interface GigabitEthernet0/42
description Uplink to BRCORE01-32nd-C3560G Gi0/41
switchport trunk encapsulation dot1q
switchport trunk native vlan 3

switchport trunk allowed vlan 1-7
switchport mode trunk

there are no other connection bet these 2 switches

Giuseppe Larosa Mon, 09/06/2010 - 06:41

Hello Yeow,

>> r u saying that i should just shutdown this interface ??

I said the opposite : do not touch the link based on our experience

post

show spanning-tree interface gi0/42 detail

I would like to understand if there are additional STP features configured and enabled or not

given your configuration it looks like there are not additional features

but they could have been configured at global level

Hope to help

Giuseppe

yeow_km Tue, 09/07/2010 - 20:05

login to the switch to check on the logs.

luckily the error is not showing now.

apparently the cisco network assistant keep trigging the historical error logs and send out emails relating to the error.

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