Enabling rapid-pvst

This post is about my attempts to enable rapid-pvst (802.1w) on one of my switch blocks at work. My previous attempt had resulted in lots of loopback errors disabling up-links on the access switches.

My only thought at the time was that perhaps I had way too many end-to-end VLANs that took too long to converge. Now, having read up on rapid-pvst , I now believe it was probably the fact that during the process of enabling rapid-pvst, the default pvst has to be switched off and for a small period you are running without any spanning tree. If you have enough traffic then the probability is high that you could get a loop during this interval. It could still be a combination of effects though and since my original failure, I have been agressive with switchport trunk allow vlans ... to restrict the number of end-to-end VLANs and have been rewarded with success.

I now have managed to get rapid-pvst working on one of the switch blocks to which I originally had problems with. This time though, knowing more I took a cautious approach.

• Step 1, Enable loopback errdisable recovery so that if for some reason the original problem reoccurred I wouldn't have to get console access to my access switches or reboot them. This can be done with errdisable recovery cause loopback
  
• Step 2, Turn on consoles message so I can see any errors that might occur. (terminal monitor)
• Step 3, Enabled rapid-pvst and wait spanning-tree mode rapid-pvst
• Step 4, Save your work once switch is stable.

I noticed on each access layer switch, the management interface went down and came back up. Once I had completed all the access layer switches, I then did the core switch (only one) and once finished I had a stable switchblock running rapid-pvst. Here is the output of show span vlan 188:

VLAN0188
  Spanning tree enabled protocol rstp
  Root ID    Priority    24764
             Address     001b.8f97.2180
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    24764  (priority 24576 sys-id-ext 188)
             Address     001b.8f97.2180
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1               Desg FWD 4         128.1    P2p
Gi0/2               Desg FWD 4         128.2    P2p
Gi0/3               Desg FWD 4         128.3    P2p
Gi0/4               Desg FWD 4         128.4    P2p
Gi0/5               Desg FWD 4         128.5    P2p
Gi0/6               Desg FWD 4         128.6    P2p
Gi0/7               Desg FWD 4         128.7    P2p
Gi0/8               Desg FWD 4         128.8    P2p
Gi0/9               Desg FWD 4         128.9    P2p
Gi0/10              Desg FWD 4         128.10   P2p
Gi0/11              Desg FWD 4         128.11   P2p
Gi0/12              Desg FWD 4         128.12   P2p
Gi0/17              Desg FWD 19        128.17   P2p Edge
Gi0/27              Desg FWD 4         128.27   P2p Peer(STP)
Gi0/28              Desg FWD 4         128.28   P2p Peer(STP)

This switch block is one of the ones that I had the loopback issue with so I am happy to have gotten it working here. I will now rinse and repeat and see if I can get it working everywhere!