Cisco 2950 port probelm

Posted on 2007-07-25
Medium Priority
Last Modified: 2010-04-12
My company has 4 cisco 2950 switches and 4 3com switches. This just started happening last week where the 3com switches seem to give out, but then come back up after a while.  I did notice that the port the crossover cable is plugged into on the Cisco switch will go amber at that point.  I look at the log and the crossover cable port is going up and down, but when I look at the interface, is shows line up protocol up.  This seems to happen every day at the same time.  We have tried switching ports where the crossover cable was plugged into on the cisco switch and the same thing happens.

Any ideas of where I can even start looking? This all started last week!  I originally though it was a bad 3com switch, I got a new one, plugged that in and the same thing happened.  That's the only network change that happened.

Thank you in advance
Question by:cas_three
LVL 50

Expert Comment

by:Don Johnston
ID: 19569459
Could be a spanning-tree issue. Maybe a rouge switch is being introduced and trying to become the root.

When it's happening, look at the spanning-tree data. See if you've got ports that are listening or learning. Also verify that the root is still where it's supposed to be.

Assisted Solution

aaron757 earned 400 total points
ID: 19569685
Don't forget to also change he cross-over cable. Sometimes it's the simplest things that cause the biggest issues just because we overlook them. If it still happens after this then you can rule out the physical medium for connectivity.

Author Comment

ID: 19573329
Thank you both!  We have already changed the cross-over cable, hoping it was something as simple as that, but no luck.  I'll look into the spanning-tree data and see what I can find there.

Is that something that would happen at the same time every day though?

Thank you!
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Expert Comment

by:Don Johnston
ID: 19573476
No. But if someone has a switch in their office and it's hooked up to a power strip and they turn in on when they come in...

It's a stretch, but it's possible.

Author Comment

ID: 19573482
We are a very small company, about 20 people, no one has any switches in their office.  But I'll check it out to be 100% positive.

Would be nice if the log gave you a little more detail.  I'm a novice user when it comes to Cisco equipment, so please bear with me.

Thank you!

Author Comment

ID: 19573614
I'm sorry to have to ask this, but I'm not sure what I should be looking for with spanning tree.  I did a show spanning-tree and this is what it comes up with:

  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     0012.7f1e.c540
             Cost        38
             Port        24 (FastEthernet0/24)
             Hello Time   2 sec  Max Age 20 sec  Forward De

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext
             Address     0012.7f1e.cbc0
             Hello Time   2 sec  Max Age 20 sec  Forward De
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------
Fa0/2            Desg FWD 19        128.2    P2p
Fa0/3            Desg FWD 19        128.3    P2p
Fa0/5            Desg FWD 19        128.5    P2p
Fa0/6            Desg FWD 19        128.6    P2p
Fa0/7            Desg FWD 19        128.7    P2p
Fa0/8            Desg FWD 19        128.8    P2p
Fa0/9            Desg FWD 19        128.9    P2p
Fa0/11           Desg FWD 19        128.11   P2p

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------

Fa0/13           Desg FWD 19        128.13   P2p
Fa0/14           Desg FWD 19        128.14   P2p
Fa0/15           Desg FWD 19        128.15   P2p
Fa0/16           Desg FWD 19        128.16   P2p
Fa0/17           Desg FWD 19        128.17   P2p
Fa0/18           Desg FWD 19        128.18   P2p
Fa0/19           Desg FWD 19        128.19   P2p
Fa0/20           Desg FWD 19        128.20   P2p
Fa0/22           Desg FWD 19        128.22   P2p
Fa0/23           Desg FWD 19        128.23   P2p
Fa0/24           Root FWD 19        128.24   P2p

Port Fa0/9 is the crossover cable that's plugged into a 3com switch.  The root port is a crossover cable plugged into another Cisco 2950 switch, we have had no problems with that port, just thought the information might be helpful.

Here is the info from show spanning-tree summary:

 Cisco-3#show spanning-tree summary
Switch is in pvst mode
Root bridge for: none
EtherChannel misconfig guard is enabled
Extended system ID           is enabled
Portfast Default             is disabled
PortFast BPDU Guard Default  is disabled
Portfast BPDU Filter Default is disabled
Loopguard Default            is disabled
UplinkFast                   is disabled
BackboneFast                 is disabled
Pathcost method used         is short

Name                   Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0001                     0         0        0         19         19
---------------------- -------- --------- -------- ---------- ----------
1 vlan                       0         0        0         19         19

No changes have been made recently.

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Accepted Solution

Don Johnston earned 1600 total points
ID: 19574085
Just keep this in mind the next time you have the problem. When it happens again, compare the results. If they're the same, it's not a spanning-tree related issue. If they're different, then you've got a new switch or link that's causing the problem.

Author Comment

ID: 19574101
So from the results above, everything looks normal and good?

As I mentioned, this seems to happen at the same time everyday, around 2:00pm.  I will keep an eye out and run the same commands if/when it happens again.

Thank you!
LVL 50

Expert Comment

by:Don Johnston
ID: 19574153
Impossible to say without a complete network diagram and spanning-tree output for every switch.

But that doesn't matter. What matters is that unless you know of a new switch or link, there shouldn't be any changes in spanning-tree output.

Expert Comment

ID: 20142560
This isn't really adding much to the question but if you only have 20~ hosts why do you have 8 switches.  One 2950 properly equip is capable of servicing the 20 hosts you have.

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