01-05-2010 01:58 AM - edited 03-06-2019 09:09 AM
Hi All,
There are 3 switces stacked & spanning-tree root primary for one vlan is configured on it. One of the stack port showing as the STP inconsistance state.
Name Interface Inconsistency
-------------------- ---------------------- ------------------
VLAN0001 StackPort3 Loop Inconsistent
Number of inconsistent ports (segments) in the system : 1
As I beleive the stack port should not be part of spanning tree calculation.
Can anyone help me how to troubleshoot this issue. Till now there is no issue but I fear that there may be a loop if it is not resolved.
Thanks & Regards
Sachi
01-05-2010 03:10 AM
Hi Sachi,
This message is normal and doesnt mean you have any loop inconsistency. Its just because STP makes the Stacking port asof the current state.
You dont have to worry about it, its normal.
HTH,
Mohamed
01-05-2010 03:27 AM
Thanks Mohamed,
But the stack port should always be in forwarding mode right? Do we need to do any specific spanning tree configuration for the master switch.
Thanks
Sachi
01-05-2010 04:07 AM
Hello Sachi,
I've checked on one of our stacks and I have 0 incosistent ports
sh spanning-tree inconsistentports
Name Interface Inconsistency
-------------------- ---------------------- ------------------
Number of inconsistent ports (segments) in the system : 0
sh switch
Current
Switch# Role Mac Address Priority State
--------------------------------------------------------
1 Slave 0013.c35a.c900 10 Ready
2 Slave 0013.c4fc.4680 1 Ready
*3 Master 0013.80b5.b280 9 Ready
4 Slave 0013.c34c.3e00 8 Ready
so something has gone wrong in your stack.
Hope to help
Giuseppe
01-05-2010 04:18 AM
Thanks Giuseppe,
I doubt on the stack cable (UDLD). Let me replace it when I get an outage & check. Otherwise there may be a problem with the stack port itself. In that case I may need to replace the switch.
Thanks
Sachi
01-05-2010 05:00 AM
Guiseppe & Sachi,
The state is irrelevant here, this is Stack port and is used to sync STP information between Stack members.
HTH
Mohamed
01-05-2010 05:27 AM
This could also be a bug:
CSCsx64925 Loopguard config should not be applied to stack ports
CSCee40722 Spanning-tree loopguard causes loops and multiple root ports
Could you attach a show version?
Do you have loopguard enabled globally?
Thanks,
01-05-2010 06:39 AM
Hi,
Pls find the sh ver
QTR-TECH-TBDC-AS-001#sh ver
Cisco IOS Software, C3750 Software (C3750-IPBASE-M), Version 12.2(25)SEE3, RELEA
SE SOFTWARE (fc2)
Copyright (c) 1986-2007 by Cisco Systems, Inc.
Compiled Thu 22-Feb-07 15:04 by myl
Image text-base: 0x00003000, data-base: 0x00EE40E0
ROM: Bootstrap program is C3750 boot loader
BOOTLDR: C3750 Boot Loader (C3750-HBOOT-M) Version 12.2(25r)SEE4, RELEASE SOFTWA
RE (fc1)
QTR-TECH-TBDC-AS-001 uptime is 16 weeks, 16 hours, 4 minutes
System returned to ROM by error - Debug Exception (Could be NULL pointer derefer
ence) Exception (0x2000)!, PC 0x9060D8
System restarted at 20:11:19 DST Mon Sep 14 2009
System image file is "flash:c3750-ipbase-mz.122-25.SEE3.bin"
cisco WS-C3750G-48PS (PowerPC405) processor (revision F0) with 118784K/12280K by
tes of memory.
Processor board ID FOC1107Z5JM
Last reset from power-on
2 Virtual Ethernet interfaces
156 Gigabit Ethernet interfaces
The password-recovery mechanism is enabled.
512K bytes of flash-simulated non-volatile configuration memory.
Base ethernet MAC Address : 00:1B:2A:F0:3E:80
Motherboard assembly number : 73-10216-08
Power supply part number : 341-0108-03
Motherboard serial number : FOC11070C7Q
Power supply serial number : DCA1104A0VR
Model revision number : F0
Motherboard revision number : C0
Model number : WS-C3750G-48PS-S
System serial number : FOC1107Z5JM
Top Assembly Part Number : 800-26853-01
Top Assembly Revision Number : B0
Version ID : V05
CLEI Code Number : CNMWN00ARC
Hardware Board Revision Number : 0x09
Switch Ports Model SW Version SW Image
------ ----- ----- ---------- ----------
1 52 WS-C3750G-48PS 12.2(25)SEE3 C3750-IPBASE-M
2 52 WS-C3750G-48PS 12.2(25)SEE3 C3750-IPBASE-M
* 3 52 WS-C3750G-48PS 12.2(25)SEE3 C3750-IPBASE-M
Yes Loopguard is enabled globaly.
Thanks
Sachi
01-05-2010 06:49 AM
I think the bug CSCsx64925 due to which stack ports are blocked by loopguard configured globaly. which first found in 12.2(46). My switch image is 12.2(25). It is fixed in 12.2(50)
Thanks a lot for the input I will upgrade the image.
Thanks & regards
Sachi
01-05-2010 10:24 AM
The hardware of the stack port cannot block, and they cannot introduce a loop either. BPDUs are sent across the stack port to synchronize STP across the members of the stack, but the forwarding across the stack does not rely on STP at all. In fact, there are several normal scenarios where the state of the stack port will be blocking. In fact, you should not see them at all in your show spanning-tree output. It's there only because you enable "debug spanning-tree event", the whole stack port should be hidden.
Now, I don't know of a case where a stack port ends up "loop inconsistent". That might well be a bug indeed, as mentioned earlier. All I can say is that your fear of loops across the stack are not realistic;-) Don't worry!
Regards,
Francois
01-05-2010 06:54 AM
You could also try to remove global loopguard and enable them individually on interfaces except on the Stack ports
HTH,
Please rate useful posts!
07-12-2011 04:42 PM
I experienced a spanning-tree meltdown related to this bug. A link-flap triggered it, causing two different switches in the stack to assume root-bridge for all their vlans. This resulted in a loop that took down the network. I saw the loop inconsistent state recently on a 3-stack of 3750's, which we cleared by rebooting. I'd recommend an upgrade to 12.2(50) to get around it.
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