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Community Member

Prunning with VTP transparent

I have a switch connected to the other 2 that form a core.

VLAN 306 is created in the 3 switchs (level 2) and allowed their passage through the trunks. The configurations are identical on both sides of the trunk. The confiuración the VTP is identical in the 3 switchs:

VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 215
VTP Operating Mode              : Transparent
VTP Domain Name                 : UPGRADE
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled

But if you observe the following information in the final swtich you can see that something is not fit:

SW18#sh spanning-tree vlan 306

VLAN0306
  Spanning tree enabled protocol ieee
  Root ID    Priority    8498
             Address     00d0.03b8.7400
             Cost        3004
             Port        2 (GigabitEthernet1/0/2)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    49458  (priority 49152 sys-id-ext 306)
             Address     001c.b075.c300
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300
  Uplinkfast enabled

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi1/0/1          Altn BLK 3004      128.1    P2p

Gi1/0/2          Root FWD 3004      128.2    P2p                 <-- here appears G11/0/2 FWD

Fa1/0/32         Desg FWD 3019      128.36   Edge P2p

SW18#
SW18#sh int gi1/0/2 trunk

Port        Mode         Encapsulation  Status        Native vlan
Gi1/0/2     on           802.1q         trunking      1

Port        Vlans allowed on trunk
Gi1/0/2     1,152,306,309-311,313,353,374,400-401,406,601,618-619,804,860

Port        Vlans allowed and active in management domain
Gi1/0/2     1,152,
306,309-311,313,353,374,400-401,406,601,618-619,804,860

Port        Vlans in spanning tree forwarding state and not pruned
Gi1/0/2     152,310,374,400,406,618,804,860                            <--- missing vlan 306

What could be happening?

Regards.

15 REPLIES
Purple

Re: Prunning with VTP transparent

  Do you have an active port in vlan 306 ?   Connect a device in vlan 306 and see if it shows u p...

Re: Prunning with VTP transparent

Do you have any port on this switch assigned to vlan 306?

Hall of Fame Super Blue

Re: Prunning with VTP transparent

slandeira wrote:

I have a switch connected to the other 2 that form a core.

VLAN 306 is created in the 3 switchs (level 2) and allowed their passage through the trunks. The configurations are identical on both sides of the trunk. The confiuración the VTP is identical in the 3 switchs:

VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 215
VTP Operating Mode              : Transparent
VTP Domain Name                 : UPGRADE
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled

But if you observe the following information in the final swtich you can see that something is not fit:

SW18#sh spanning-tree vlan 306

VLAN0306
  Spanning tree enabled protocol ieee
  Root ID    Priority    8498
             Address     00d0.03b8.7400
             Cost        3004
             Port        2 (GigabitEthernet1/0/2)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    49458  (priority 49152 sys-id-ext 306)
             Address     001c.b075.c300
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300
  Uplinkfast enabled

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi1/0/1          Altn BLK 3004      128.1    P2p

Gi1/0/2          Root FWD 3004      128.2    P2p                 <-- here appears G11/0/2 FWD

Fa1/0/32         Desg FWD 3019      128.36   Edge P2p

SW18#
SW18#sh int gi1/0/2 trunk

Port        Mode         Encapsulation  Status        Native vlan
Gi1/0/2     on           802.1q         trunking      1

Port        Vlans allowed on trunk
Gi1/0/2     1,152,306,309-311,313,353,374,400-401,406,601,618-619,804,860

Port        Vlans allowed and active in management domain
Gi1/0/2     1,152,
306,309-311,313,353,374,400-401,406,601,618-619,804,860

Port        Vlans in spanning tree forwarding state and not pruned
Gi1/0/2     152,310,374,400,406,618,804,860                            <--- missing vlan 306

What could be happening?

Regards.

Is the question you are asking is why does the switch prune a vlan if the switch is in VTP transparent mode ?

If so, as far as i know, if you enable VTP pruning and then make the switch transparent it will still actually prune. Is this what you did ?

Jon

Cisco Employee

Re: Prunning with VTP transparent

Hello Jon,

Your answer intrigues me. Are you suggesting that even in VTP Transparent mode, the VTP Pruning is effective? That does not seem logical to me. I can imagine the neighbors of a VTP Transparent switch to prune off all pruning-eligible VLANs from the trunks towards the VTP Transparent switch, because the VTP Pruning relies on processing the VTP Join messages and such messages shall not be processed or generated by a VTP Transparent switch. Following the same logic, a VTP Transparent switch would also have pruned all pruning-eligible VLANs from its trunks.

Still, this is just a theory - I don't have any switch handy right now to confirm this but personally, I would expect that if the switch runs in VTP Transparent mode, the VTP Pruning setting should be ignored and the VTP Transparent switch should not prune any VLANs from its trunks. Its neighbors, of course, will prune them because they will not receive any VTP Join messages from a VTP Transparent switch.

Best regards,

Peter

Hall of Fame Super Blue

Re: Prunning with VTP transparent

Peter

To be honest i would have thought the same but i seem to remember coming across this before. If the switches are set as VTP transparent then vtp pruning will not have any effect. But if the switches are originally VTP server/client and VTP pruning is enabled and then the switches are changed to VTP transparent then VTP pruning still is in effect.

I might well have remembered wrongly and i too don't have switches handy to test with but it would explain what the original poster is seeing.

Come to think of it i do have some switches buried away upstairs so if i am at a loss for something to do this weekend i might have a quick look

Jon

Cisco Employee

Re: Prunning with VTP transparent

Jon,

Thank you for your kind reply I remember the VTP Pruning having some sort of "hysteresis" when activated or deactivated. It shall be definitely worth having a look. But please don't spoil your weekend with such ... particularities

Thanks! It's great to be in touch with you again.

Best regards,

Peter

Community Member

Re: Prunning with VTP transparent

Thanks for your answers.


I tried what you said in 2 switches in the laboratory and once you switch to VTP Transparent, automatically pass all vlans to spanning tree forwarding state and not pruned. ¿?¿?¿?


I do not understand anything at all ... Someone thinks of another explanation?

Cisco Employee

Re: Prunning with VTP transparent

Hello,

Can you perhaps post the entire sanitized configuration of your switch together with the show vlan brief output? Without seeing more exact information, it is very difficult to diagnose what's going on.

Best regards,

Peter

Community Member

Re: Prunning with VTP transparent

Ok!! the config and show vlan brief!!

Core:SWH00 and SWH01

End Switch: SWH18

Cisco Employee

Re: Prunning with VTP transparent

Hello,

This is interesting indeed. On the SWH18, can you please issue these commands once more and post the output?

  • show spanning-tree vlan 306
  • show spanning-tree int gi1/0/1
  • show spanning-tree int gi1/0/2
  • show spanning-tree root
  • show int trunk

Thanks!

Best regards,

Peter

Community Member

Re: Prunning with VTP transparent

Here's the data. Anyway I think I'll open a case ...

Cisco Employee

Re: Prunning with VTP transparent

Hello,

Hmm, this surely is a strange issue. Does your VLAN 306 experience connection errors, or is just the show int trunk output incorrect? In any case, I think that this issue is worth handing off to the TAC to see their suggestion. I would be very much interested in hearing their opinion!

Best regards,

Peter

Hall of Fame Super Silver

Re: Prunning with VTP transparent

Hello,

I don't see anything strange

STP priority are set on a per vlan basis:

hostname SWH01
spanning-tree vlan 186,188,190,192,194,196,198,300,302,304,306 priority 8192

hostname SWH00

spanning-tree vlan 306,308,310,312,314,316,318,320,322,324,326 priority 16384

for vlan 306 interface to SWH00 is in alternate blocking this is correct if gi1/0/1 is directed to SWH00

SWH18#show spanning-tree vlan 306

VLAN0306
  Spanning tree enabled protocol ieee
  Root ID    Priority    8498  =  8192 +306
             Address     00d0.03b8.7400
             Cost        3004
             Port        2 (GigabitEthernet1/0/2)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    49458  (priority 49152 sys-id-ext 306)
             Address     001c.b075.c300
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300
  Uplinkfast enabled

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi1/0/1          Altn BLK 3004      128.1    P2p
Gi1/0/2          Root FWD 3004      128.2    P2p
Fa1/0/32         Desg FWD 3019      128.36   Edge P2p

I think what we see here is absolutely correct because SWH01 is root bridge for this vlan.

So vlan 306 cannot be in the third list in sh trunk for g1/0/1 because it is not in forwarding state it is alternate blocking

Suggestion: on interface description I usually put also the port of the neighbor like switchname:portx/y

Hope to help

Giuseppe

Hall of Fame Super Blue

Re: Prunning with VTP transparent

Giuseppe

It's not gi1/0/1 we are talking about though. We are talking about gi1/0/2 which is forwarding but not showing vlan 306 as forwarding in the "sh int trunk" output.

Jon

Hall of Fame Super Silver

Re: Prunning with VTP transparent

Hello Jon,

sorry I should have thought it couldn't be so easy!

Best Regards

Giuseppe

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