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adding a catalyst 3500 XL switch to a cat 3750 switch stack

Posted on 2011-02-21
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Last Modified: 2012-06-27
I have added actually 2 cisco catalyst 3500 XL series switches to our current Catalyst 3750 switch stack (in which we have 5 x 3750's in the stack).  I was looking at the spanning-tree summary on one of the 3500's and it say that there are 27 ports in blocked mode.  How can that be?  Wouldn't any workstation connected to those blocked ports not have network access?  Or is that not how it works?  Also, something is not configured correctly, can someone enlighten me?  Thanks!

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Question by:cansib
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Expert Comment

by:Don Johnston
ID: 34948010
please post the output of a show span and indicate which port is connected to the 3750.
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Expert Comment

by:gambith
ID: 34948217
how is everything connected? remember that the stack act's as one big switch.. there should be no ethernet cables between them, just the back  big cable.... the 3500, how are they connected to to the 3750's ?

blocked mode stops traffic from those "TRUNK" or ACCESS ports to avoid a loop on the LAN. if you post more info we can help u out :D
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Author Comment

by:cansib
ID: 34954974
Hi,

Thanks for the replies.  Yes, the stack is all connected via their stack cables.  This 3500 is connected to the top switch in the stack through GBIC modules on both the stack switch and the 3500.  So the stack switch is GB2 and the 3500 switch is GB1 for ports.

BottomSwitch#sho span sum

UplinkFast is disabled


Name                 Blocking Listening Learning Forwarding STP Active
-------------------- -------- --------- -------- ---------- ----------
VLAN1                27       0         0        23         50
-------------------- -------- --------- -------- ---------- ----------
              1 VLAN 27       0         0        23         50

BottomSwitch#
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Author Comment

by:cansib
ID: 34954999
Here is the brief summary....

BottomSwitch#sho span bri

VLAN1
  Spanning tree enabled protocol IEEE
  ROOT ID    Priority 24577
             Address 001f.c91f.5780
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32768
             Address     0007.0ec0.ca00
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec


Port                           Designated
Name    Port ID Prio Cost Sts  Cost  Bridge ID      Port ID
------- ------- ---- ---- ---  ----  -------------- -------
Fa0/1   128.13  128  19   FWD  4     0007.0ec0.ca00 128.13
Fa0/2   128.14  128  100  BLK  4     0007.0ec0.ca00 128.14
Fa0/3   128.15  128  19   FWD  4     0007.0ec0.ca00 128.15
Fa0/4   128.16  128  100  BLK  4     0007.0ec0.ca00 128.16
Fa0/5   128.17  128  19   BLK  4     0007.0ec0.ca00 128.17
Fa0/6   128.18  128  100  BLK  4     0007.0ec0.ca00 128.18
Fa0/7   128.19  128  19   FWD  4     0007.0ec0.ca00 128.19
Fa0/8   128.20  128  100  BLK  4     0007.0ec0.ca00 128.20
Fa0/9   128.22  128  19   FWD  4     0007.0ec0.ca00 128.22
Fa0/10  128.23  128  100  BLK  4     0007.0ec0.ca00 128.23
Fa0/11  128.24  128  100  BLK  4     0007.0ec0.ca00 128.24
Fa0/12  128.25  128  19   FWD  4     0007.0ec0.ca00 128.25
Fa0/13  128.26  128  19   FWD  4     0007.0ec0.ca00 128.26
Fa0/14  128.27  128  19   FWD  4     0007.0ec0.ca00 128.27
Fa0/15  128.28  128  19   FWD  4     0007.0ec0.ca00 128.28
Fa0/16  128.29  128  19   FWD  4     0007.0ec0.ca00 128.29
Fa0/17  128.31  128  19   FWD  4     0007.0ec0.ca00 128.31
Fa0/18  128.32  128  19   FWD  4     0007.0ec0.ca00 128.32
Fa0/19  128.33  128  19   FWD  4     0007.0ec0.ca00 128.33
Fa0/20  128.34  128  19   FWD  4     0007.0ec0.ca00 128.34
Fa0/21  128.35  128  19   FWD  4     0007.0ec0.ca00 128.35
Fa0/22  128.36  128  19   FWD  4     0007.0ec0.ca00 128.36
Fa0/23  128.37  128  19   FWD  4     0007.0ec0.ca00 128.37
Fa0/24  128.38  128  100  BLK  4     0007.0ec0.ca00 128.38
Fa0/25  128.40  128  100  BLK  4     0007.0ec0.ca00 128.40
Fa0/26  128.41  128  19   FWD  4     0007.0ec0.ca00 128.41
Fa0/27  128.42  128  19   FWD  4     0007.0ec0.ca00 128.42
Fa0/28  128.43  128  100  BLK  4     0007.0ec0.ca00 128.43
Fa0/29  128.44  128  100  BLK  4     0007.0ec0.ca00 128.44
Fa0/30  128.45  128  100  BLK  4     0007.0ec0.ca00 128.45
Fa0/31  128.46  128  100  BLK  4     0007.0ec0.ca00 128.46
Fa0/32  128.47  128  100  BLK  4     0007.0ec0.ca00 128.47
Fa0/33  128.49  128  100  BLK  4     0007.0ec0.ca00 128.49
Fa0/34  128.50  128  19   FWD  4     0007.0ec0.ca00 128.50
Fa0/35  128.51  128  100  BLK  4     0007.0ec0.ca00 128.51
Fa0/36  128.52  128  100  BLK  4     0007.0ec0.ca00 128.52
Fa0/37  128.53  128  100  BLK  4     0007.0ec0.ca00 128.53
Fa0/38  128.54  128  100  BLK  4     0007.0ec0.ca00 128.54
Fa0/39  128.55  128  100  BLK  4     0007.0ec0.ca00 128.55
Fa0/40  128.56  128  100  BLK  4     0007.0ec0.ca00 128.56
Fa0/41  128.58  128  100  BLK  4     0007.0ec0.ca00 128.58
Fa0/42  128.59  128  100  BLK  4     0007.0ec0.ca00 128.59
Fa0/43  128.60  128  100  BLK  4     0007.0ec0.ca00 128.60
Fa0/44  128.61  128  19   FWD  4     0007.0ec0.ca00 128.61
Fa0/45  128.62  128  100  BLK  4     0007.0ec0.ca00 128.62
Fa0/46  128.63  128  19   FWD  4     0007.0ec0.ca00 128.63
Fa0/47  128.64  128  19   FWD  4     0007.0ec0.ca00 128.64
Fa0/48  128.65  128  100  BLK  4     0007.0ec0.ca00 128.65
Gi0/1   128.67  128  4    FWD  0     001f.c91f.5780 128.2
Gi0/2   128.75  128  100  BLK  4     0007.0ec0.ca00 128.75

BottomSwitch#
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Author Comment

by:cansib
ID: 34955108
So, if a port is down or not being used, does it automatically go to a Blocked state in Spanning Tree?  Because I notice the Blocked entries coincide with the ports that are listed as down when you do a sho ip int brief.
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Author Comment

by:cansib
ID: 34956657
So, I'm not even sure I have a real problem.  Anyone have anything to add?  Thanks!

Mark
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Accepted Solution

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Don Johnston earned 250 total points
ID: 34956665
If there's nothing connected to the blocked ports, then there's nothing to worry about.
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Author Comment

by:cansib
ID: 34956776
Ok, so I am going to add another 3500 switch......  : )

Is there anything I should be aware of before plugging it in?  This one will be a bit different.  It will be in another room (temporarily) so I will be plugging the ethernet cable into another GB port on one of the stack switches (3750) and from there, to a patch panel, then at the cooresponding wall jack in the other room, be plugging into a GB port on the 3500 switch.

The reason I am concerned is that I have done this already and things seemed fine most of the day, but then users reported a brief network outage (everything, internet, our SQL servers, Exchange... etc.) during the middle of the day so I came back into the office and unplugged that switch and it there hasn't been any issues since.  Could this switch have created a Spanning Tree loop or something with the other 3500 switch or with all of the switches?

bpdu guard is on basically on every port on the switch stack, is this optimal?

Thanks!

Mark
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Assisted Solution

by:gambith
gambith earned 250 total points
ID: 34956791
Just make sure is not on server mode, also that the revision is lower than the one u are connecting to..
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