Rapid STP states vs show spanning tree output (RSTP blocking?)

[wags]

We migrated to RSTP long ago with normal/expected tweaks.  I've never taken the time to review things in detail because the end result was the same thing STP did decades ago, prevent L2 loops.  However we recently noticed slow convergence times during an "IOS update induced hiccup" and we needed to go back and look closer.  So I started showing spanning-tree.  I thought we had RSTP enabled correctly and it looks like we do, but the display (below from L2 switch) shows blocked state, at least as I read it. 

https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/24062-146.html#anc4  Port states list in the Cisco Doc does not list blocked as a valid state for RSTP.

Since a blocking state is not valid in RSTP, is this an IOS left over "display feature"?    Am I misunderstanding the display output? 

Thanks In Advance, Ron

Further data:  Topology is 3 switches, 1 being L2 and 2 being L3 running L3 standby redundancy.    The L3 switches have similar ST displays.   All ST displays actually show what we would expect given our ST tuning, but the "BLK" state implies we are still running 1D. 

 L2-switch#sh spanning-tree

VLAN2200
Spanning tree enabled protocol rstp
Root ID Priority 26776
Address 00c1.64c7.2600
Cost 3002
Port 257 (TenGigabitEthernet3/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 51352 (priority 49152 sys-id-ext 2200)
Address 0081.c40b.1340
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
UplinkFast enabled but inactive in rapid-pvst mode

Interface Role   Sts   Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te3/1     Root   FWD 3002 128.257 P2p
Te3/5     Altn    BLK 3002 128.261 P2p

[balaji.bandi]

Do you have any small diagram how this connected to understand the topology.

[wags]

No I don't.  I guess also I need to be more specific with my questions. 

While running RSTP, does IOS "show spanning-tree" commands still show state of blocking (an invalid RSTP state) vs the valid discarding RSTP state?

[balaji.bandi]

Technically does not matter what you use, if you have alternative path in Layer 2 broadcast domain, the based on STP election process one of the path will be blocked if it see as loop.

[wags]

Yes that is correct, but the display of spanning-tree is showing the STP state blocking vs the RSTP state discarding for the link. The display showing STP states would imply the switch may be using STP vs RSTP, even though it says RSTP earlier in the display.  After decades of doing Cisco, it would not be the first time I've seen an IOS feature somehow fall back and the only way you know about it is a strange display output.

While running RSTP, does IOS "show spanning-tree" commands still show state of blocking (an invalid RSTP state) vs the valid discarding RSTP state?

Can someone show their known RSTP looped network and see if they to are getting blocking as a state?  Or even better can someone show their known RSTP looped network and see if they have any discarding states?

[MHM Cisco World]

Can I see show spanning tree 

I think thr port the show blk not dis is one connect to stp not rstp' there is compatibility between two mode'

But let me see show spanning to be sure

MHM

[wags]

The original post has the show spanning-tree output. Did you want something else?  All devices associated with the vlan show "exactly" the same, give or take.  All say enabled RSTP, UplinkFast enabled but inactive in rapid-pvst mode, and link states that depending, show blocking vs discarding.

[MHM Cisco World]

Te3/5 this port lead to other SW'

Can I see show spanning tree of that SW.

MHM

[wags]

Of course I cannot find that specific switch right now, I didn't write down its IP.  So here is a set of them.  Note the root is down a different port for this switch

L2-switch-12#sh spanning vlan 2200

VLAN2200
Spanning tree enabled protocol rstp
Root ID Priority 26776
Address 00c1.64c7.2600
Cost 3002
Port 261 (TenGigabitEthernet3/5)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 51352 (priority 49152 sys-id-ext 2200)
Address 00a6.caa0.4900
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
UplinkFast enabled but inactive in rapid-pvst mode

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te3/1 Altn BLK 3002 128.257 P2p
Te3/5 Root FWD 3002 128.261 P2p

L3-switch off port T3/5, root bridge

L3-switch-2#sh spanning-tree vlan 2200

VLAN2200
Spanning tree enabled protocol rstp
Root ID Priority 26776
Address 00c1.64c7.2600
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 26776 (priority 24576 sys-id-ext 2200)
Address 00c1.64c7.2600
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 480

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te2/1 Desg FWD 2 128.129 P2p
Te2/2 Desg FWD 2 128.130 P2p
Te2/3 Desg FWD 2 128.131 P2p
Te2/4 Desg FWD 2 128.132 P2p
Te2/5 Desg FWD 2 128.133 P2p
Te2/6 Desg FWD 2 128.134 P2p
Te2/7 Desg FWD 2 128.135 P2p
Te2/8 Desg FWD 2 128.136 P2p
Te2/9 Desg FWD 4 128.137 P2p
Te2/10 Desg FWD 2 128.138 P2p

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

Te2/11 Desg FWD 2 128.139 P2p
Te2/12 Desg FWD 2 128.140 P2p
Te2/13 Desg FWD 2 128.141 P2p
Te2/14 Desg FWD 2 128.142 P2p
Te2/15 Desg FWD 2 128.143 P2p
Te2/16 Desg FWD 2 128.144 P2p
Te2/17 Desg FWD 2 128.145 P2p
Te2/18 Desg FWD 4 128.146 P2p
Te2/19 Desg FWD 2 128.147 P2p
Te2/30 Desg FWD 2 128.158 P2p

L3-switch-1 off port T3/1

L3-switch-1#sh spanning vlan 2200

VLAN2200
Spanning tree enabled protocol rstp
Root ID Priority 26776
Address 00c1.64c7.2600
Cost 2
Port 158 (TenGigabitEthernet2/30)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 30872 (priority 28672 sys-id-ext 2200)
Address 00c1.64c7.2c00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 480

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te2/1 Desg FWD 2 128.129 P2p
Te2/2 Desg FWD 2 128.130 P2p
Te2/3 Desg FWD 2 128.131 P2p
Te2/4 Desg FWD 2 128.132 P2p
Te2/5 Desg FWD 2 128.133 P2p
Te2/6 Desg FWD 2 128.134 P2p
Te2/7 Desg FWD 2 128.135 P2p
Te2/8 Desg FWD 2 128.136 P2p
Te2/9 Desg FWD 4 128.137 P2p
Te2/10 Desg FWD 2 128.138 P2p
Te2/11 Desg FWD 2 128.139 P2p
Te2/12 Desg FWD 2 128.140 P2p
Te2/13 Desg FWD 2 128.141 P2p
Te2/14 Desg FWD 2 128.142 P2p
Te2/16 Desg FWD 2 128.144 P2p
Te2/17 Desg FWD 2 128.145 P2p
Te2/18 Desg FWD 4 128.146 P2p
Te2/19 Desg FWD 2 128.147 P2p
Te2/30 Root FWD 2 128.158 P2p

[MHM Cisco World · Accepted solution]

All these years I never see discard status' but you rise this case.

It appear that all IOS not show this status instead it show BLK.

So different is stp (legacy) show listening and learning but rstp show only BLK and then FWD.

More check link below 

https://community.cisco.com/t5/routing/problem-with-port-state-discarding-in-rstp/td-p/4078036

MHM

[wags]

It appears other folks empirically believe that the display spanning-tree shows STP link states while running RSTP.  I would agree.

I did identify our issue and we are in fact running RSTP "everywhere" and displays show STP states of BLOCKING instead RSTP of DISCARDING.  At least at the current versions of IOS.

[Giuseppe Larosa]

Hello @wags ,

>> While running RSTP, does IOS "show spanning-tree" commands still show state of blocking (an invalid RSTP state) vs the valid discarding RSTP state?

Yes it can still show BLK blocked for reasons that can be an higher STP cost to the root bridge or in your case

>> Te3/1 Root FWD 3002 128.257 P2p
Te3/5 Altn BLK 3002 128.261 P2p

The STP path cost to the root is the same 3002, but Te3/5 is selected as Alternate Blocking because it has an higher worse Port ID 128.261 > 128.257

Port Te3/1 is selected as Root Port and it is in forwarding state for its lower Port ID.

Port ID is made of port piority default value is 128 and then a value that is SNMP ifindex of the port.

if Te3/1 fails Te3/5 will be promoted to Root port status and it will move to forwarding state using the RSTP  handshake mechanism with the neighbor.

So what you see is normal even with RSTP

Hope to help

Giuseppe

[wags]

Gopinath_Pigili, they are all running RSTP per "exact same output" on display of all 3.  All say RSTP at the top, but depending show states of blocking where it would be appropriate.  And same kind of thing on well over 1000 campus area switches in my network. 

 Giuseppe, Everything you say is what I believe to be correct as well.  However, the display should be RSTP compliant if you are actually running RSTP IMO.    The display output is still showing STP states vs RSTP states and that bugs me because of my past baggage with IOS.  I'll wait a bit to see if others have thoughts, but I may go ahead and open a TAC case to get the reasoning behind the display not being RSTP "complaint" when running RSTP,  if in fact there is not something wrong with our configs. 

After decades with Ciscoisms, I never assume that I am correct, or that Cisco's code is "clean".

[Blue_Bird]

It is recommended...all the swithes should run with RSTP to get the benfit of faster convergence....

RSTP is backward compatible with STP.....if one switch is configured with STP another switch is  RSTP....it will lose its faster convergence benifit...and acts as STP..... 

Best regards
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