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SG302-08P & MSTP problem

We've just added some of the SG302 switches to an existing network of (mostly) 2950 switches - to provide some PoE ports for wireless APs.

After configuring MSTP identically to that on the existing network, it looks like the SG302 switches can't handle the pre-standard MSTP from the older switches and are forming their own tree/domain. Or it could be that I just don't understand what I'm seeing ! I'd appreciate some help.

 

 

On one of the 2950 :

MST01
  Spanning tree enabled protocol mstp
  Root ID    Priority    24577
             Address     000c.ceac.a700
             Cost        40000
             Port        25 (GigabitEthernet0/1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000c.852d.8540
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 0  

Interface        Port ID                     Designated                Port ID
Name             Prio.Nbr      Cost Sts      Cost Bridge ID            Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Gi0/1            128.25       20000 FWD     20000 32769 000c.852d.6bc0 128.25  
Gi0/2            128.26       20000 FWD     40000 32769 000c.852d.8540 128.26

That looks fine, it's correctly identified the root bridge (a 3550) and route to it.

 

On an SF302 attached to it, I get this :

###### MST 1 Vlans Mapped: 1

Root ID        Priority    32768                      
               Address     00:e1:6d:8f:d1:b1
               This switch is the regional Root
Interfaces
Name       State     Prio.Nbr   Cost      Sts  Role  PortFast  Type
--------   --------  --------   --------- ---- ----  --------  ----------
...

gi1        enabled   128.49     20000     Frw  Mstr  No        P2P Bound (RSTP)

 

This looks to me like it's oblivious to the real tree root and has elected itself.

 

But for instance 0, it does seem to recognise the master :

###### MST 0 Vlans Mapped: 99
CST Root ID    Priority    24576
               Address     00:0c:ce:ac:a7:00
               Path Cost   20000
               Root Port   gi1
               This switch is the IST master
               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
Bridge ID      Priority    32768
               Address     00:e1:6d:8f:d1:b1
               Hello Time  2 sec  Max Age 20 sec  Forward Delay 15 sec
               Max hops    20 
  Name     State   Prio.Nbr    Cost    Sts   Role PortFast       Type        
--------- -------- --------- -------- ------ ---- -------- ----------------- 
...

gi1       enabled  128.49    20000    Frw    Root No       P2P Bound (RSTP)  

 

 

Configs :

2950 :

sho spanning-tree mst configuration
Name      [main]
Revision  1
Instance  Vlans mapped
---------------------------------------------------------------------
0         2-99,300-4094
1         1
2         100-299
---------------------------------------------------------------------
 
And on the 302 :
sho spanning-tree mst-configuration
Gathering information ..........
Current MST configuration
Name: main
Revision: 1
Instance  Vlans Mapped                                       State
--------  ------------------------------------------------   -----
0         99                                                 enabled
1         1                                                  enabled
2         100-299                                            enabled

 

 

At the moment I've left ports administratively shutdown to avoid any potential loops, but I was hoping as part of the extra work we've done to add some redundancy. Am I missing something ?

Simon

 

 

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