[c-nsp] Maximum spannig tree instances

[Peter Rathlev]

On Mon, 2009-07-13 at 23:38 +0200, Nicolas Rolans wrote:
> This supportwiki article [snip] could be what you're looking for. I
> confirm the 1800 instances/slot limit.

... but it doesn't say anything about the number of STP instances.

I tested it on a Sup720 SXI1 and could create more than 1800 STP
instances with the VLANs split among two modules:

r2(config)#do sh vlan vir


Slot 4
-------
Total slot virtual ports 1799

Slot 5
-------
Total slot virtual ports 1799

Total chassis virtual ports 3598
r2(config)#do sh spann summ tot
Switch is in rapid-pvst mode
Root bridge for: VLAN0100-VLAN0110, VLAN0115-VLAN0118, VLAN0120-VLAN0131
  VLAN0133-VLAN0297, VLAN0500-VLAN0999, VLAN1021-VLAN2281, VLAN2300-VLAN2337
  VLAN2400-VLAN4000
EtherChannel misconfig guard            is enabled
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 enabled
PVST Simulation Default                 is enabled but inactive in rapid-pvst mode
Bridge Assurance                        is enabled
UplinkFast                              is disabled
BackboneFast                            is disabled
Pathcost method used                    is long

Name                   Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
3598 vlans                   0         0        0       3598       3598
r2(config)#

I got this message during the configuration:

%SW_VLAN-SP-4-VTP_SEM_BUSY: VTP semaphore is unavailable for function sw_vlansp_get_4k_vlan_info. Semaphore locked by download info

After deleting the VLANs and trying the same again the message did not
appear, so I guess it's nothing really bad.

It seems that more then 1800 instances are possible. I didn't have more
than a two module (Sup720-10G + 6724-SFP) configuration to test this on
at hand.

My bold guess would be that the system limit for number of STP instances
is 10000/13000 total virtual ports (RPVST/PVST).

Whether having 1800+ STP instances on the same switch is a good idea i
something completely different. :-)

Regards,
Peter