09-16-2013 03:48 AM - edited 03-04-2019 09:02 PM
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?
09-19-2013 03:04 AM
Anyone? I guess it may be hard to tell from the info I have given
09-19-2013 05:53 AM
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.
09-19-2013 07:04 AM
Cheers for the reply John - I'll take a look at that cmd ouput.
09-19-2013 07:37 AM
Out of curiosity, where the the spanning tree root?
09-19-2013 07:43 AM
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.
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