Spanning tree max instance

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May 5th, 2010
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Hi there,



I have 4 3560 connected to core 3750 with 2gb portchannel.

I do have 244 VLANs on my network and from what i know you can only have 128 on spanning tree instance.

After running show spanning-tree command i can se that only half of my vlans are listed.

Is this means on the other half i will have a broadcast storms and other wierd stuff ?


How can i spann for all the vlans ?




Kind regards

marcin

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francisco_1 Wed, 05/05/2010 - 05:42
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are all your vlans listed in the vlan database as active?. do "show vlan brief"


If there is no port forwarding traffic in a vlan, stp instance will not be created for that vlan.

francisco_1 Wed, 05/05/2010 - 05:50
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like i said if there is no active port forwarding in a vlan, then no stp instance for that vlan when you look at stp info on the switch you will only see stp info for vlans with active port forwarding traffic.


Also you can have a max 128 instance, you have more vlans that max instance on the switch. do you need all vlans?

Jon Marshall Wed, 05/05/2010 - 06:03
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marcin.piesio wrote:


Yes, all my vlans are listed as active.


Marcin


Unless you are daisy chaining switches where a vlan is needed on a remote switch so you have to include it on the intermediate switch or unless you are running trunks on all ports with devices that need access to all 244 vlans then i can't see why each switch needs to have all 244 vlans active. Like i said with 48 ports per switch how can you need 244 vlans per switch.


Jon

marcin.piesio Wed, 05/05/2010 - 07:40
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3560 ports are trunk connected to coax ip switches which are connected to 12 devices.

Every device have to be on seperate vlan. We will have 20 of of those coax switches = 21*12=252 and we will "only" use 244.

So not all the switches need access to all 244 vlans, but this eventually connects to the core which should be a root bridge for all vlans and it cannot because of 128 limitation.


Is my MSTP design below makes sense ?


From what i understand you specify region for a pool of vlans ?

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Jon Marshall Wed, 05/05/2010 - 05:45
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marcin.piesio wrote:


Hi there,



I have 4 3560 connected to core 3750 with 2gb portchannel.

I do have 244 VLANs on my network and from what i know you can only have 128 on spanning tree instance.

After running show spanning-tree command i can se that only half of my vlans are listed.

Is this means on the other half i will have a broadcast storms and other wierd stuff ?


How can i spann for all the vlans ?




Kind regards

marcin

Marcin


You would have to make sure there is no loop for any vlan that does not have an STP instance running.


If you have more than 128 STP instances then you need to either -


1) look if your switch actually needs all 244 vlans. Considering there are only 48 ports on each switch then it is unlikely you need all 244 vlans on each switch. If you clear the vlan off any trunk links to a switch, assuming the switch does not have any ports in that vlan, then STP will not run on a vlan for a switch that has no active ports in that vlan.


2) alternatively you could look at implementing MSTP which allows yhou to groups vlans together and only run one STP instance for each grroup -


3750 MSTP


Jon

francisco_1 Wed, 05/05/2010 - 05:51
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According to Jon's suggestion, you might have to use MSTP.



Francisco.

marcin.piesio Wed, 05/05/2010 - 06:03
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Dont ask me why but yes we need all 244.

There are no loops on the network, my only concern is that port channel is already redundant link so the question is now can portchannel creating switching loops ?


thanks for your quick response

Marcin

Jon Marshall Wed, 05/05/2010 - 06:34
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marcin.piesio wrote:


Dont ask me why but yes we need all 244.

There are no loops on the network, my only concern is that port channel is already redundant link so the question is now can portchannel creating switching loops ?


thanks for your quick response

Marcin

Marcin


If you really do need all 244 vlans on each switch and i can;t see why you would then i would suggest looking at MSTP as per previous thread so that you can run STP on all vlans.


Portchannel could in theory create a loop, that is why STP should be run on all vlans. It is your L2 failsafe.


Jon

marcin.piesio Wed, 05/05/2010 - 07:47
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3560 ports are trunk connected to coax ip switches which are connected to 12 devices.

Every device have to be on seperate vlan. We will have 20 of of those coax switches = 21*12=252 and we will "only" use 244.

So not all the switches need access to all 244 vlans, but this eventually connects to the core which should be a root bridge for all vlans and it cannot because of 128 limitation.


Is my MSTP design below makes sense ?


From what i understand you specify region for a pool of vlans ?

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marcin.piesio Thu, 05/13/2010 - 02:31
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Hi there,


can some please help me with my mst config:



sw1(running rapid-pvst) directly connected to sw2(running mst)



sw1 is root for vlans range 1-100  (about 30 vlans in range)


sw2 is root for vlans 101-350


sw2

mst config

instance 0 vlan 7,19,88,101-350

instance 1 vlan 1-6,8-18,20-87,89-4094


trunk between sw1 and sw2 config

switchport trunk encapsulation dot1q
switchport mode trunk


when enabling trunk i receive msg

%SPANTREE-2-PVSTSIM_FAIL: Blocking root port Gi0/24: Inconsitent inferior PVST BPDU received on VLAN 4, claiming root 24580:0022.55bb.1500


and sh spann output


sh spanning-tree


MST0
  Spanning tree enabled protocol mstp
  Root ID    Priority    24577
             Address     0022.55bb.1500
             Cost        20008
             Port        24 (GigabitEthernet0/24)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec


  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)
             Address     ec44.7643.4980
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec


Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/24              Root BKN*20000     128.24   P2p Bound(PVST) *PVST_Inc




MST2
  Spanning tree enabled protocol mstp
  Root ID    Priority    32770
             Address     ec44.7643.4980
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec


  Bridge ID  Priority    32770  (priority 32768 sys-id-ext 2)
             Address     ec44.7643.4980
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec


Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/24              Mstr BKN*20000     128.24   P2p Bound(PVST) *PVST_Inc





when i unplug and plug the cable again it doesn't block the link and it works. sh spann output below



sh spanning-tree


MST0
  Spanning tree enabled protocol mstp
  Root ID    Priority    24577
             Address     0022.55bb.1500
             Cost        20008
             Port        24 (GigabitEthernet0/24)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec


  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)
             Address     ec44.7643.4980
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec


Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/24              Root FWD 20000     128.24   P2p Bound(PVST) *PVST_Inc




MST2
  Spanning tree enabled protocol mstp
  Root ID    Priority    32770
             Address     ec44.7643.4980
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec


  Bridge ID  Priority    32770  (priority 32768 sys-id-ext 2)
             Address     ec44.7643.4980
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec


Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/24              Mstr BKN*20000     128.24   P2p Bound(PVST) *PVST_Inc





can you please explain why does it fail on first attempt ?



i want to limit my trunk to vlan only vlans 7,19 and 88 by applying below config

switchport trunk allowed vlan 7,19,88 when enable link mst blocks it.


is there anything i am missing in my config to make it work ?



thanks for your response

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