Procurve 2910al MSTP to Cisco SG500 MSTP not playing fair

[RouterGuy]

Hello.  I am encountering a really hair-tearing issue here.  I have a stack of HP 2910al running MSTP and a stack of Cisco SG500X units running MSTP.

I have identically configured instances and can show that the base spanning-tree process is recognizing that there is some topology change when i change the switch priority.  The can trade off who is the CST Root.  I am, however, unable to get the instance on the HP switch to recognize who is root.

I cannot pass traffic on any vlan, (except for native VL1).

Here we can see the HP 2910 switch recognizes the cisco switch as being the root (the basic spanning tree sees the designated bridge):

HP-SW-1(config)# sh spanning-tree           

 Multiple Spanning Tree (MST) Information

  STP Enabled   : Yes
  Force Version : MSTP-operation
  IST Mapped VLANs : 2-9,11-19,21-29,31-99,101-109,111-799,801-4094
  Switch MAC Address : 38eaa7-75a780
  Switch Priority    : 8192
  Max Age  : 20
  Max Hops : 20   
  Forward Delay : 15

  Topology Change Count  : 5           
  Time Since Last Change : 5 mins      

  CST Root MAC Address : d4d748-ccac1a  < - The Cisco 500
  CST Root Priority    : 4096        
  CST Root Path Cost   : 60000       
  CST Root Port        : 1                  

  IST Regional Root MAC Address : 38eaa7-75a780  < -  MY HP 2910
  IST Regional Root Priority    : 8192        
  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
  ----- --------- + --------- ---- ---------- + ------------- ---- --- ----
  1     100/1000T | 20000     64   Forwarding | 00147c-488b40 2    Yes No    

BUT HERE, the HP switch sees itself to be the root bridge for the instance #1 – and the designated bridge is the HP2910 itself…

MP-SW-1(config)# sh spanning-tree instance 1

 MST Instance Information

  Instance ID : 1
  Mapped VLANs : 1,10,20,30,100,110,800
  Switch Priority         : 8192

  Topology Change Count   : 5           
  Time Since Last Change  : 9 mins      

  Regional Root MAC Address : 38eaa7-75a780
  Regional Root Priority    : 8192        
  Regional Root Path Cost   : 0           
  Regional Root Port        : This switch is root
  Remaining Hops            : 20          

                                                             Designated
  Port  Type      Cost      Priority Role       State        Bridge
  ----- --------- --------- -------- ---------- ------------ --------------
  1     100/1000T 20000     128      Master     Forwarding   38eaa7-75a780     


Here’s my HP configuration (with fluff removed):

interface 1
   name "Cisco Stack"
   no power-over-ethernet
   exit

vlan 10
   name "Management"
   tagged 1,Trk1-Trk2    < - NOTE: Vlan’s are all tagged on VL1
   ip address 172.16.10.1 255.255.255.0
   exit

spanning-tree
spanning-tree 1 priority 4
spanning-tree Trk1 priority 4
spanning-tree Trk2 priority 4
spanning-tree config-name "Irvine"
spanning-tree config-revision 1
spanning-tree instance 1 vlan 1 10 20 30 100 110 800
spanning-tree instance 1 Trk1 priority 4
spanning-tree instance 1 Trk2 priority 4
spanning-tree priority 2

The Cisco SX500 is not as robust of a CLI set as the commercial 3560’s etc.  But here’s the way this unit looks:

spanning-tree mode mst
spanning-tree priority 4096
spanning-tree mst configuration
instance 1 vlan 1,10,20,30,100,110,800
name Irvine
revision 1
exit
spanning-tree mst 1 priority 4096
vlan database                                         
vlan 10,20,30,100,110,800
interface gigabitethernet1/1/1
 description "To other Core"
 spanning-tree link-type point-to-point
 spanning-tree mst 1 cost 20000
 switchport trunk allowed vlan add 10,20,30,100,110,800

[Fredrik Lönnman]

I would guess this has to do with VLAN 1 not beeing allowed on the SG500 trunk. Also you might still have a problem if VLAN1 is tagged from the HP but untagged (native per default) on the SG500.

[RouterGuy]

I'd agree that there would be a problem if VL1 was blocked - but it is the only VLAN that is passing.  I have VL10 set up as my management VLAN and have the appropriate L3 SVI's on each side.  Should work.

I'm looking for any hints and tidbits!

[RouterGuy · Accepted solution]

BTW - VL1 is untagged (native) on both sides.

[Fredrik Lönnman]

According to your config, gigabitethernet1/1/1 on the Cisco is not allowing VLAN1. Doesn't matter if its the native VLAN, if its no inte allowed list it wont be used.

[Richard Brodie_1]

I would check the MSTP configuration digests on both switches, if you are seeing multiple regional roots.

[Pete W]

Agreed - start with checking that the MSTP Digests match:

Cisco : show spanning-tree mst digest

HP : show spanning-tree mst-config

Regards,

Pete

[RouterGuy]

Hi guys - - thanks for the advice.  The syntax for the show spanning-tree mst digest does not really exist on the SG500X switch.  HOWEVER, with this comment, I did observe that the HP switch shows a RATHER LONG 0xNNNNNNNNNNNNNNN digest key.  The Cisco does NOT.

Any other suggestions?

Oh, the advertised or permitted VLANS are identical and the revision is identical and the domain name is identical. 

[RouterGuy]

Oh yes it is permitted. VL1 is a very special VL. By default it is the native VL and will be passed. In this case, if VL1 was NOT passed, I would have NO access to the Cisco switch as it is cross-connected to the HP switch and that is how I have my management access.

[RouterGuy]

Here is the cisco equivalent to the suggested digest command:

switchccac1a#sh spanning-tree mst-configuration
Gathering information ..........
Current MST configuration
Name: Irvine
Revision: 1
Instance  Vlans Mapped                                       State
--------  ------------------------------------------------   -----
1         1,10,20,30,100,110,800                             enabled
switchccac1a#

For the HP, this is what I see:

IRV_SHORETEL-0(config)# sh spanning-tree mst-config

 MST Configuration Identifier Information

  MST Configuration Name : Irvine                            MST Configuration Revision : 1      MST Configuration Digest : 0x4211DA627F7479E5EDD3B93099652B67

  IST Mapped VLANs : 2-9,11-19,21-29,31-99,101-109,111-799,801-4094

  Instance ID Mapped VLANs                                               ----------- ---------------------------------------------------------   1           1,10,20,30,100,110,800