Per a recent question I recently configured both my HP (2x 2900) and Cisco (1x 3750) hardware to use MSTP for interoperability. I thought this was functional until I applied the change to the third device (HP switch 1 below) at which time the spanning tree root started flapping causing performance issues (5% packet loss) between my two HP switches. I'm not sure why.

HP Switch 1 A4 connected to Cisco 1/0/1. HP Switch 2 B2 connected to Cisco 2/0/1. HP Switch 1 A2 connected to HP Switch 2 A1. I'd prefer the Cisco stack to act as the root.

EDIT:

There is one specific line - 'spanning-tree 1 path-cost 500000' in the HP switch 2 that I didn't add and was preexisting. I'm not sure if it could have the kind of impact that I'm describing. I'm more a security and monitoring guy then networking.

EDIT 2:

I'm starting to believe the problem lies in the fact that the value for my MST 0 instance on the Cisco is still at the default 32768. I worked up a diagram: This is based on every show command I could find for STP. I'll make this change after hours and see if it helps.

Cisco 3750 Config:

version 12.2

spanning-tree mode mst
spanning-tree extend system-id
spanning-tree mst configuration
 name mstp
 revision 1
 instance 1 vlan 1, 40, 70, 100, 250
spanning-tree mst 1 priority 0
vlan internal allocation policy ascending

interface TenGigabitEthernet1/1/1
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface TenGigabitEthernet2/1/1
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface Vlan1
 no ip address
!
interface Vlan100
 ip address 192.168.100.253 255.255.255.0
!

Cisco 3750 show spanning tree:

show spanning-tree

MST0
  Spanning tree enabled protocol mstp
  Root ID    Priority    32768
             Address     0004.ea84.5f80
             Cost        200000
             Port        53 (TenGigabitEthernet1/1/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32768  (priority 32768 sys-id-ext 0)
             Address     a44c.11a6.7c80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te1/1/1             Root FWD 2000      128.53   P2p


MST1
  Spanning tree enabled protocol mstp
  Root ID    Priority    1
             Address     a44c.11a6.7c80
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    1      (priority 0 sys-id-ext 1)
             Address     a44c.11a6.7c80
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Te1/1/1             Desg FWD 2000      128.53   P2p

Cisco 3750 show logging:

%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to down
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan100, changed state to down
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan100, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to down
%LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up

HP Switch 1:

; J9049A Configuration Editor; Created on release #T.13.71
vlan 1
   name "DEFAULT_VLAN"
   untagged 1-8,10,13-16,18-23,A1-A4
   ip address 100.100.100.17 255.255.255.0
   no untagged 9,11-12,17,24
   exit
vlan 100
   name "192.168.100"
   untagged 9,11-12,17,24
   tagged 1-8,10,13-16,18-23,A1-A4
   no ip address
   exit
vlan 21
   name "Users_2"
   tagged 1,A1-A4
   no ip address
   exit
vlan 40
   name "Cafe"
   tagged 1,4,7,A1-A4
   no ip address
   exit
vlan 250
   name "Firewall"
   tagged 1,4,7,A1-A4
   no ip address
   exit
vlan 70
   name "DMZ"
   tagged 1,4,7-8,13,A1-A4
   no ip address
   exit
spanning-tree
spanning-tree config-name "mstp"
spanning-tree config-revision 1
spanning-tree instance 1 vlan 1 40 70 100 250
password manager
password operator

HP Switch 1 show spanning tree:

 show spanning-tree

 Multiple Spanning Tree (MST) Information

  STP Enabled   : Yes
  Force Version : MSTP-operation
  IST Mapped VLANs : 2-39,41-69,71-99,101-249,251-4094
  Switch MAC Address : 0021f7-126580
  Switch Priority    : 32768
  Max Age  : 20
  Max Hops : 20
  Forward Delay : 15

  Topology Change Count  : 363,490
  Time Since Last Change : 14 hours

  CST Root MAC Address : 0004ea-845f80
  CST Root Priority    : 32768
  CST Root Path Cost   : 200000
  CST Root Port        : 1

  IST Regional Root MAC Address : 0021f7-126580
  IST Regional Root Priority    : 32768
  IST Regional Root Path Cost   : 0
  IST Remaining Hops            : 20

  Root Guard Ports     :
  TCN Guard Ports      :
  BPDU Protected Ports :
  BPDU Filtered Ports  :
  PVST Protected Ports :
  PVST Filtered Ports  :

                  |           Prio            | Designated    Hello
  Port  Type      | Cost      rity State      | Bridge        Time PtP Edge
  ----- --------- + --------- ---- ---------- + ------------- ---- --- ----
  A1              | Auto      128  Disabled   |
  A2    10GbE-CX4 | 2000      128  Forwarding | 0021f7-126580 2    Yes No
  A3    10GbE-CX4 | Auto      128  Disabled   |
  A4    10GbE-SR  | Auto      128  Disabled   |

HP Switch 1 Logging: I removed the date / time fields since they are inaccurate (no NTP configured on these switches)

00839 stp: MSTI 1 Root changed from 0:a44c11-a67c80 to 32768:0021f7-126580
00839 stp: MSTI 1 Root changed from 32768:0021f7-126580 to 0:a44c11-a67c80
00842 stp: MSTI 1 starved for an MSTI Msg Rx on port A4 from 0:a44c11-a67c80
00839 stp: MSTI 1 Root changed from 0:a44c11-a67c80 to 32768:0021f7-126580
00839 stp: MSTI 1 Root changed from 32768:0021f7-126580 to 0:a44c11-a67c80
00839 stp: MSTI 1 Root changed from 0:a44c11-a67c80 to ...

HP Switch 2 Configuration:

; J9146A Configuration Editor; Created on release #W.14.49

vlan 1
   name "DEFAULT_VLAN"
   untagged 1,3-17,21-24,A1-A2,B2
   ip address 100.100.100.36 255.255.255.0
   no untagged 2,18-20,B1
   exit
vlan 100
   name "192.168.100"
   untagged 2,18-20
   tagged 1,3-17,21-24,A1-A2,B1-B2
   no ip address
   exit
vlan 21
   name "Users_2"
   tagged 1,A1-A2,B2
   no ip address
   exit
vlan 40
   name "Cafe"
   tagged 1,13-14,16,A1-A2,B2
   no ip address
   exit
vlan 250
   name "Firewall"
   tagged 1,13-14,16,A1-A2,B2
   no ip address
   exit
vlan 70
   name "DMZ"
   tagged 1,13-14,16,A1-A2,B2
   no ip address
   exit
logging 192.168.100.18
spanning-tree
spanning-tree 1 path-cost 500000
spanning-tree config-name "mstp"
spanning-tree config-revision 1
spanning-tree instance 1 vlan 1 40 70 100 250

HP Switch 2 Spanning Tree:

show spanning-tree

 Multiple Spanning Tree (MST) Information

  STP Enabled   : Yes
  Force Version : MSTP-operation
  IST Mapped VLANs : 2-39,41-69,71-99,101-249,251-4094
  Switch MAC Address : 0024a8-cd6000
  Switch Priority    : 32768
  Max Age  : 20
  Max Hops : 20
  Forward Delay : 15

  Topology Change Count  : 21,793
  Time Since Last Change : 14 hours

  CST Root MAC Address : 0004ea-845f80
  CST Root Priority    : 32768
  CST Root Path Cost   : 200000
  CST Root Port        : A1

  IST Regional Root MAC Address : 0021f7-126580
  IST Regional Root Priority    : 32768
  IST Regional Root Path Cost   : 2000
  IST Remaining Hops            : 19

  Root Guard Ports     :
  TCN Guard Ports      :
  BPDU Protected Ports :
  BPDU Filtered Ports  :
  PVST Protected Ports :
  PVST Filtered Ports  :

                  |           Prio            | Designated    Hello
  Port  Type      | Cost      rity State      | Bridge        Time PtP Edge
  ----- --------- + --------- ---- ---------- + ------------- ---- --- ----
  A1    10GbE-CX4 | 2000      128  Forwarding | 0021f7-126580 2    Yes No
  A2    10GbE-CX4 | Auto      128  Disabled   |
  B1    SFP+SR    | 2000      128  Forwarding | 0024a8-cd6000 2    Yes No
  B2              | Auto      128  Disabled   |

HP Switch 2 Logging: I removed the date / time fields since they are inaccurate (no NTP configured on these switches)

00839 stp: CST Root changed from 32768:0021f7-126580 to 32768:0004ea-845f80
00839 stp: IST Root changed from 32768:0021f7-126580 to 32768:0024a8-cd6000
00839 stp: CST Root changed from 32768:0004ea-845f80 to 32768:0024a8-cd6000
00839 stp: CST Root changed from 32768:0024a8-cd6000 to 32768:0004ea-845f80
00839 stp: CST Root changed from 32768:0004ea-845f80 to 32768:0024a8-cd6000
00435 ports: port B1 is Blocked by STP
00839 stp: CST Root changed from 32768:0024a8-cd6000 to 32768:0021f7-126580
00839 stp: IST Root changed from 32768:0024a8-cd6000 to 32768:0021f7-126580
00839 stp: CST Root changed from 32768:0021f7-126580 to 32768:0004ea-845f80