Hello, The config are in the

Dave Tremblay · ‎07-20-2015

Hello,

Very annoying behavior between a C3650 (IOS-XE 03.03.04SE) and a C2950T (121-22.EA14) . I have an MST spanning-tree with 2 instances (MST0 and 1). Same configuration in both but as soon as connect the C2950T on a simple trunk (copper wire CAT6), the state on the C3650 goes from forwarding to blocking (dispute) and I loose communication with the C2950T switch. It's doing that with my other C2950T switch also. I connect my switch to another C2960G switch and no problem at all. I've configured the ports to be "spanning-tree pre-standard" also.

There is no unidirectionnal issue, port goes auto 1000-FULL. I'm kind of lost right now and debug does'nt give anything.

Thanks in advance for your suggestions.

devils_advocate · ‎07-21-2015

Hi Dave

Can you post the configuration of both switches?

Also post the results of:

#show span

Thanks

Dave Tremblay · ‎07-21-2015

Hello,

The config are in the attached files. Here's the result for "show span" in both switches when I connect them together.

C2950T-1#show spanning-tree

MST00
Spanning tree enabled protocol mstp
Root ID    Priority    32768
             Address     000c.85e0.3a40
             This bridge is the root
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    32768 (priority 32768 sys-id-ext 0)
             Address     000c.85e0.3a40
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2            Desg FWD 200000    128.2    Edge P2p
Fa0/3            Desg FWD 200000    128.3    Edge P2p
Fa0/4            Desg FWD 200000    128.4    Edge P2p
Fa0/5            Desg FWD 2000000   128.5    Edge Shr
Fa0/7            Desg FWD 200000    128.7    Edge P2p
Fa0/8            Desg FWD 200000    128.8    Edge P2p
Fa0/9            Desg FWD 200000    128.9    Edge P2p
Fa0/10           Desg FWD 200000    128.10   Edge P2p
Fa0/20           Desg FWD 200000    128.20   Edge P2p

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------

Fa0/21           Desg FWD 200000    128.21   Edge P2p
Fa0/22           Desg FWD 200000    128.22   Edge P2p
Fa0/24           Desg FWD 200000    128.24   Edge P2p
Gi0/1            Desg FWD 20000     128.25   P2p

MST01
Spanning tree enabled protocol mstp
Root ID    Priority    61441
             Address     000c.85e0.3a40
             This bridge is the root
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    61441 (priority 61440 sys-id-ext 1)
             Address     000c.85e0.3a40
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2            Desg FWD 200000    128.2    Edge P2p
Fa0/3            Desg FWD 200000    128.3    Edge P2p
Fa0/4            Desg FWD 200000    128.4    Edge P2p
Fa0/5            Desg FWD 2000000   128.5    Edge Shr
Fa0/7            Desg FWD 200000    128.7    Edge P2p
Fa0/8            Desg FWD 200000    128.8    Edge P2p
Fa0/9            Desg FWD 200000    128.9    Edge P2p
Fa0/10           Desg FWD 200000    128.10   Edge P2p
Fa0/20           Desg FWD 200000    128.20   Edge P2p

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------

Fa0/21           Desg FWD 200000    128.21   Edge P2p
Fa0/22           Desg FWD 200000    128.22   Edge P2p
Fa0/24           Desg FWD 200000    128.24   Edge P2p
Gi0/1            Desg FWD 20000     128.25   P2p

C2950T-1#

**************************************************************************************************

C3650-1#show spanning-tree

MST0
Spanning tree enabled protocol mstp
Root ID    Priority    0
             Address     70ca.9b5e.6080
             Cost        0
             Port        28 (TenGigabitEthernet1/1/4)
             Hello Time   2 sec Max Age 20 sec Forward Delay 5 sec

Bridge ID Priority    32768 (priority 32768 sys-id-ext 0)
             Address     74a2.e6cd.0380
             Hello Time   2 sec Max Age 20 sec Forward Delay 5 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/12            Desg FWD 20000     128.12   P2p
Gi1/0/21            Desg FWD 20000     128.21   P2p
Gi1/0/22            Desg BLK 20000     128.22   P2p Dispute Pre-STD
Te1/1/4             Root FWD 2000      128.28   P2p

MST1
Spanning tree enabled protocol mstp
Root ID    Priority    1
             Address     70ca.9b5e.6080
             Cost        2000
             Port        28 (TenGigabitEthernet1/1/4)
             Hello Time   2 sec Max Age 20 sec Forward Delay 5 sec

Bridge ID Priority    4097   (priority 4096 sys-id-ext 1)
             Address     74a2.e6cd.0380
             Hello Time   2 sec Max Age 20 sec Forward Delay 5 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/12            Desg FWD 20000     128.12   P2p
Gi1/0/21            Desg FWD 20000     128.21   P2p
Gi1/0/22            Desg BLK 20000     128.22   P2p Dispute Pre-STD
Te1/1/4             Root FWD 2000      128.28   P2p

C3650-1#

MST state to DISPUTE between C3650 and C2950T