spanning tree mstp porta are blacking.

[R Manjunatha]

One of the access switch ASW-2 interfaces f0/0 and f0/1 blocking state after configuring mstp , it shows type  P2p Bound(PVST). Is that default pvst enabled for this switch?

ASW-2

spanning-tree mode mst
spanning-tree extend system-id
!
spanning-tree mst configuration
name mstp
revision 10
instance 1 vlan 10, 20, 30
instance 2 vlan 40, 50, 60
!
spanning-tree mst 1-2 priority 28672
!
vlan internal allocation policy ascending

interface Ethernet0/0
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface Ethernet0/1
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface Ethernet0/2
switchport access vlan 30
switchport mode access
switchport port-security maximum 2
switchport port-security mac-address sticky
spanning-tree portfast edge
spanning-tree bpduguard enable
!
interface Ethernet0/3
switchport access vlan 40
switchport mode access
switchport port-security maximum 2
switchport port-security mac-address sticky
spanning-tree portfast edge
spanning-tree bpduguard enable

ASW-2#sh spa summ
Switch is in mst mode (IEEE Standard)
Root bridge for: MST1-MST2
Extended system ID is enabled
Portfast Default is disabled
Portfast Edge BPDU Guard Default is disabled
Portfast Edge BPDU Filter Default is disabled
Loopguard Default is disabled
PVST Simulation is enabled
Bridge Assurance is enabled
EtherChannel misconfig guard is enabled
Configured Pathcost method used is short (Operational value is long)
UplinkFast is disabled
BackboneFast is disabled

Name Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
MST0 2 0 0 10 12
MST1 2 0 0 1 3
MST2 2 0 0 1 3
---------------------- -------- --------- -------- ---------- ----------
3 msts 6 0 0 12 18

ASW-2#sh spanning-tree mst

##### MST0 vlans mapped: 1-9,11-19,21-29,31-39,41-49,51-59,61-4094
Bridge address aabb.cc00.0900 priority 32768 (32768 sysid 0)
Root address aabb.cc00.0700 priority 32768 (32768 sysid 0)
port Et0/1 path cost 2000100
Regional Root this switch
Operational hello time 2 , forward delay 15, max age 20, txholdcount 6
Configured hello time 2 , forward delay 15, max age 20, max hops 20

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Et0/0 Altn BLK 2000000 128.1 P2p Bound(PVST)
Et0/1 Root BKN*2000000 128.2 P2p Bound(PVST) *PVST_Inc
Et0/2 Desg FWD 2000000 128.3 P2p Edge
Et0/3 Desg FWD 2000000 128.4 P2p Edge
Et1/0 Desg FWD 2000000 128.5 P2p
Et1/1 Desg FWD 2000000 128.6 P2p
Et1/2 Desg FWD 2000000 128.7 P2p
Et1/3 Desg FWD 2000000 128.8 P2p
Et2/0 Desg FWD 2000000 128.9 P2p
Et2/1 Desg FWD 2000000 128.10 P2p
Et2/2 Desg FWD 2000000 128.11 P2p
Et2/3 Desg FWD 2000000 128.12 P2p

##### MST1 vlans mapped: 10,20,30
Bridge address aabb.cc00.0900 priority 28673 (28672 sysid 1)
Root this switch for MST1

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Et0/0 Altn BLK 2000000 128.1 P2p Bound(PVST)
Et0/1 Mstr BKN*2000000 128.2 P2p Bound(PVST) *PVST_Inc
Et0/2 Desg FWD 2000000 128.3 P2p Edge

##### MST2 vlans mapped: 40,50,60
Bridge address aabb.cc00.0900 priority 28674 (28672 sysid 2)
Root this switch for MST2

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Et0/0 Altn BLK 2000000 128.1 P2p Bound(PVST)
Et0/1 Mstr BKN*2000000 128.2 P2p Bound(PVST) *PVST_Inc
Et0/3 Desg FWD 2000000 128.4 P2p Edge

[Peter Paluch]

Hello,

It seems that the switches that your ASW-2 connects to run PVST+ and not MST. If that is the case, there are certain rules that you must obey if you want to interoperate PVST+ and MST. In particular, based on the outputs you have shared, the root switch for VLAN 1 is in the PVST+ part of the network. To successfully interoperate PVST+ and MST in this specific scenario, it is necessary to meet these requirements:

1) If the root for VLAN 1 is in the PVST+ region then every other VLAN must also have its root switch in the PVST+ region.

2) The root switches for VLANs 2-4094 must have their priorities lower by at least 4096 from the priority of the root switch in VLAN 1.

If you cannot meet these requirements, it is not possible to interoperate PVST+ and MST, and the ports from your MST-enabled switch toward the PVST+ region will become blocked with the PVST Simulation Inconsistency reason.

In that case, the only solution would be to convert your ASW-2 to the same STP version run by the upstream switches, either PVST+ or Rapid PVST+. Overall, it is not a good idea to mix different STP versions in the same switched network.

Please feel welcome to ask further!

Best regards,
Peter

[R Manjunatha]

Hi,

I need to configure only MSTP in this scenario for all access switches and how to disable pvst + 

regards, 

[Peter Paluch]

Hello,

If you configure MSTP on all access switches but do not configure it on your distribution switches, you will still have a mixed MSTP/PVST+ environment. That one is difficult to operate because you need to comply with additional rules to allow MSTP on your access switches and PVST+ on your distribution switches to interoperate. I already mentioned those two rules for your current setup in my previous post, but I cannot recommend such design. Ideally, you should migrate all your switches, access and distribution, to the same STP variant - so either all switches to MSTP or all switches to (Rapid) PVST+.

When you ask about "how to disable PVST+", the simplified answer is: You cannot disable it. A Cisco switch that runs MSTP still falls back to PVST+ operation on an individual per-port basis if it receives PVST+ BPDUs on that port. This is precisely to facilitate the interoperation with the older PVST+. If you truly want to stop seeing any PVST+ in your network, you must migrate all your access and distribution switches to MST.

So you need to decide what you want to achieve. If you insist on keeping the distribution switches run PVST+ while running MST on the access switches, you must abide by the strict additional rules on how to set up switch priorities in different VLANs:

1) Make sure that the root switch for VLAN 1 (a distribution switch in your case) has a lower priority than any MST switch in MST instance 0.

2) Make sure that the root switches for all other VLANs (again distribution switches in your case) have a lower priority than the root switch for VLAN 1.

For example:

! DSW-1:
spanning-tree vlan 1 priority 24576
spanning-tree vlan 2-4094 priority 20480

! DSW-2:
spanning-tree vlan 1 priority 28672
spanning-tree vlan 2-4094 priority 16384

! Any access switch:
spanning-tree mst 0 priority 32768 ! the default one

Note how this configuration maintains the above two requirements in all scenarios:

- If both DSW-1 and DSW-2 are up and running, the root for VLAN1 is DSW-1 (prio 24576) and the root for all other VLANs is DSW-2 (prio 16384)

- If only DSW-1 is up, it is the root for VLAN1 (prio 24576) and all other VLANs (prio 20480)

- If only DSW-2 is up, it is the root for VLAN1 (prio 28672) and all other VLANs (prio 16384)

Best regards,
Peter

[R Manjunatha]

Hi,

Thank you for the update. This lab has minimum VLANs, so I decided to configure all switches are rapid pvst + 

DSW-1#sh standby brief
P indicates configured to preempt.
|
Interface Grp Pri P State Active Standby Virtual IP
Vl10 1 150 P Active local 192.168.10.2 192.168.10.254
Vl20 1 100 Standby 192.168.20.2 local 192.168.20.254
Vl30 1 150 P Active local 192.168.30.2 192.168.30.254
Vl40 1 100 Standby 192.168.40.2 local 192.168.40.254
Vl50 1 150 P Active local 192.168.50.2 192.168.50.254
Vl60 1 100 Standby 192.168.60.2 local 192.168.60.254

DSW-1(config)# spanning-tree vlan 10,30,50 root primary
DSW-1(config)# spanning-tree vlan 20,40,60 root secondary

DSW-2#show standby brief
P indicates configured to preempt.
|
Interface Grp Pri P State Active Standby Virtual IP
Vl10 1 100 Standby 192.168.10.1 local 192.168.10.254
Vl20 1 150 P Active local 192.168.20.1 192.168.20.254
Vl30 1 100 Standby 192.168.30.1 local 192.168.30.254
Vl40 1 150 P Active local 192.168.40.1 192.168.40.254
Vl50 1 100 Standby 192.168.50.1 local 192.168.50.254
Vl60 1 150 P Active local 192.168.60.1 192.168.60.254

DSW-2(config)#spanning-tree vlan 20,40,60 root primary
DSW-2(config)#spanning-tree vlan 10,30,50 root secondary

Enable all switch Rapid PVST

XYZ# spanning tree mode rapid PVST

ASW-1# sh spanning-tree blockedports

Name Blocked Interfaces List
-------------------- ------------------------------------
VLAN0001 Et0/1
VLAN0010 Et0/1
VLAN0020 Et0/0
VLAN0030 Et0/1
VLAN0040 Et0/0
VLAN0050 Et0/1
VLAN0060 Et0/0

ASW-2#sh spanning-tree blockedports

Name Blocked Interfaces List
-------------------- ------------------------------------
VLAN0001 Et0/0
VLAN0010 Et0/0
VLAN0020 Et0/1
VLAN0030 Et0/0
VLAN0040 Et0/1
VLAN0050 Et0/0
VLAN0060 Et0/1

ASW-3#sh spanning-tree blockedports

Name Blocked Interfaces List
-------------------- ------------------------------------
VLAN0001 Et0/1
VLAN0010 Et0/1
VLAN0020 Et0/0
VLAN0030 Et0/1
VLAN0040 Et0/0
VLAN0050 Et0/1
VLAN0060 Et0/0

[Peter Paluch · Accepted solution]

Hello,

I understand - and in this case, using Rapid PVST+ is perfectly okay.

I would like to reiterate once again that STP and its various variants - PVST+, Rapid PVST+, MSTP - is one of the protocols where mixing different versions in a single network is strongly discouraged and may require very specific additional configuration before the different STP variants can successfully interoperate. Mixing different STP versions in a single network should be avoided at all costs.

Should you have any additional questions, please feel free to ask. If you believe your question has been fully answered and resolved, please consider marking this thread as such.

Best regards,
Peter

[R Manjunatha]

Thank you very much for you Guidance to understand more about STP terminology.