Rapid Spanning Tree inconsistent?

[lcaruso]

Hi,

I have two switches claiming to be the root bridge for the same vlans. The 3750-X stack was configured to be the root for vlans present and the 2960S was brought online over the weekend to replace another one.

This is the command I used to attempt and make the 3750-X stack the root

spanning-tree vlan 1-2,10,50,101,200,900,999 root primary diameter 4 

The IOS converted that to this

spanning-tree mode rapid-pvst
spanning-tree loopguard default
spanning-tree portfast bpduguard default
spanning-tree extend system-id
spanning-tree vlan 1-2,10,50,101,200,900,999 priority 24576
spanning-tree vlan 1-2,10,50,101,200,900,999 forward-time 10
spanning-tree vlan 1-2,10,50,101,200,900,999 max-age 14

I just need the 3750-X stack to be the root for everything. What's best way to accomplish this?

Here's the 3750-X stack who thinks he's the root for vlans 2,999 (which the 2960S claims root status for)

sw1#sh span sum
Switch is in rapid-pvst mode
Root bridge for: VLAN0001-VLAN0002, VLAN0008-VLAN0010, VLAN0035, VLAN0050
  VLAN0101, VLAN0105, VLAN0200, VLAN0999
EtherChannel misconfig guard is enabled
Extended system ID           is enabled
Portfast Default             is disabled
PortFast BPDU Guard Default  is enabled
Portfast BPDU Filter Default is disabled
Loopguard Default            is enabled
UplinkFast                   is disabled
Stack port is StackPort1
BackboneFast                 is disabled
Configured Pathcost method used is short
Name                   Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0001                     0         0        0         17         17
VLAN0002                     0         0        0         10         10
VLAN0008                     0         0        0          4          4
VLAN0009                     0         0        0          8          8
VLAN0010                     0         0        0         81         81
VLAN0035                     0         0        0          1          1
VLAN0050                     0         0        0          6          6
VLAN0101                     0         0        0          5          5
VLAN0105                     0         0        0          1          1
VLAN0200                     0         0        0          1          1
VLAN0999                     0         0        0          1          1
---------------------- -------- --------- -------- ---------- ----------
11 vlans                     0         0        0        135        135

Here's the 2960S who thinks he is the root for vlans 2,200,900,999

SW2#sh span sum
Switch is in rapid-pvst mode
Root bridge for: VLAN0002, VLAN0200, VLAN0900, VLAN0999
EtherChannel misconfig guard is enabled
Extended system ID           is enabled
Portfast Default             is disabled
PortFast BPDU Guard Default  is enabled
Portfast BPDU Filter Default is disabled
Loopguard Default            is enabled
UplinkFast                   is disabled
BackboneFast                 is disabled
Configured Pathcost method used is short
Name                   Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0001                     1         0        0          2          3
VLAN0002                     0         0        0          1          1
VLAN0010                     0         0        0          2          2
VLAN0050                     0         0        0         21         21
VLAN0101                     1         0        0         22         23
VLAN0200                     0         0        0          1          1
VLAN0900                     0         0        0          1          1
VLAN0999                     0         0        0          1          1
---------------------- -------- --------- -------- ---------- ----------
8 vlans                      2         0        0         51         53

[paul driver · Accepted solution]

Hello

You have RSTP enabled - but have manipulated the max-age and forwarding time which isnt necessary as these value are not relevant for 802.1w (rstp) - also you have specified the stp root via the macro command which will only decrease stp bridge priority only when its first enabled so to become stp root-

If another switch comes on line with he same command it will then drop its value even lower than the existing stp root switch to succeed it.

I would suggest to apply the root priority manually and remove the diameter command

Primary switch:

spanning-tree vlan 1-2,10,50,101,200,900,999 priority 0

Second switch

spanning-tree vlan 1-2,10,50,101,200,900,999 priority 4096

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[lcaruso]

Hi,

Thanks for your reply. I'll try your recommended priority commands after hours.

I'm curious why the diameter command is not needed when Cisco links this command to their best practices for RPVST

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/best/practices/recommendations.html#wp1040726