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New Member

Have I got a STP problem?

Hello. Any help appreciated with this problem ...

We had a user complaining about a temporary dropped network connection. Looking at the log on the switch the host PC connects to I can see the dropped connection, and it was for a short time (about 20 secs). Now we checked the copper cabling end to end and all was ok, and previously we had a x-over'd uplink flapping on the same switch stack (x-over connections stack, not stackwise). But the logs do not show uplinks to be going down now.

Worryingly I am seeing in the logs that on a daily basis we have the same kind of brief lost connections on 3 or 4 random access ports on every switch in the chain. From the log date / time stamp + the fact the connection drop is so brief it doesn't appear to be PC reboots, I can only think it's a spanning tree issue? The logs show this happening on 1st switch in chain all the way through (this is all happening on a very old legacy leg of Cisco infrastructure btw which is due to be replaced but not sure when).

So hardware setup is:

6500 Chassis

Fiber connection from chassis to port Fa0/26 on 2950 #1 (which has a x-over to another 2950 in same cabinet)

Fibre from port Fa0/25 of that same 2950 #1 to a 2950 in another cabinet (which has another 2 x 2950's off it in a chain via x-over's)

The common log entry I'm seeing daily for random ports on all the switches is this:

Sep 10 08:37:08.203 GDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to down

Sep 10 08:37:09.211 GDT: %LINK-3-UPDOWN: Interface FastEthernet0/3, changed state to down

Sep 10 08:37:12.003 GDT: %LINK-3-UPDOWN: Interface FastEthernet0/3, changed state to up

Sep 10 08:37:14.023 GDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to up

Sep 10 08:37:25.603 GDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to down

Sep 10 08:37:30.223 GDT: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to up

The common STP configuration on all the switches is:

spanning-tree mode pvst

spanning-tree portfast default

no spanning-tree optimize bpdu transmission

spanning-tree extend system-id

And we have 'spanning-tree portfast disable' command on Fa0/1 & 0/2 and on Fa0/25 & 0/26 on all switches.

There is only one VLAN in use, although we do seem to have left over some VLAN's left showing which are showing up in spanning tree detail I guess because of pvst mode?

1    default                          active    Fa0/2, Fa0/3, Fa0/4, Fa0/5

                                                Fa0/6, Fa0/7, Fa0/8, Fa0/9

                                                Fa0/10, Fa0/11, Fa0/12, Fa0/13

                                                Fa0/14, Fa0/15, Fa0/16, Fa0/17

                                                Fa0/18, Fa0/19, Fa0/20, Fa0/21

                                                Fa0/22, Fa0/23, Fa0/24, Fa0/26

16   VLAN0016                         active

17   VLAN0017                         active

18   VLAN0018                         active

888  Native_Vlan                       active

I've looked at the STP configuration we have and it looks ok from what I've read, but I'm no expert! Can you see anything wrong?                   

5 REPLIES
New Member

Have I got a STP problem?

Anyone? I guess it may be hard to tell from the info I have given

Have I got a STP problem?

Normally, if you have a spanning tree issue, you will see "MAC Address Flaps" and or "STP Topology Changes".

Do a 'show int trunk', and if you look at 'show span int x/x' and you should be able to see the topology changes on the interfaces, such as BPDUs received. With standard PVST+, basically 802.1D, The root switch will send our BPDUs, and the RPs, on all non-root switches will receive his BPDUs, and push them out their Designated Ports. Unlke RSTP, which allows each and every switch to send out hellos every 2 seconds (kind of like a hello in a dynamic routing protocol), this doesn't happend with 802.1D (PVST+).

Since these ports in question, seem to be user ports, I would like into the computer configuration, Network cable etc. You can also do some testing as well, such as plug a laptop in to one of the port sand see if yours does the same thing etc.

I hope that helped some. Please feel free to ask more questions.

New Member

Have I got a STP problem?

Cheers for the reply John - I'll take a look at that cmd ouput.

Have I got a STP problem?

Out of curiosity, where the the spanning tree root?

Re: Have I got a STP problem?

Hello Daran,

Is portfast enabled on these ports, if not it would be best to enable it , without this feature every time a tcn occurs on the network edge ports will be affected until stp converges.

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

Please don't forget to rate any posts that have been helpful. Thanks.
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