[j-nsp] Help with MSTP in EX8208

[Octavio Alfageme]

Hello everyone,



I would be grateful if somebody could help me with a problem related to
MSTP in EX8208s running  JunOS 12.3R5. My scenario is pretty simple: 2
EX8208s connected to each other by two links (the first one, ae2.0
consisting of one GE interface and the second one,  ge-20/0/1.0).
Obviously, there is a loop. I've configured MSTP in a pretty simple way in
both EX8208s:



*test at EX8208_B> show configuration protocols mstp *

*configuration-name TEST_MSTP;*

*interface ge-20/0/1.0 {*

*    cost 1000;*

*    mode point-to-point;*

*}*

*interface ae2.0 {*

*    cost 1000;*

*    mode point-to-point;*

*}*

*msti 1 {*

*    vlan [ VLAN_200 VLAN_201 VLAN_210 VLAN_312 ];*

*}*

*msti 2 {*

*    vlan [ VLAN_3000 VLAN_3001 VLAN_4000 VLAN_4090 ];*

*}*



This way, MSTP selects EX8208_A as root bridge and EX8208_B blocks the port
ge-20/0/1 with higher port-id and same cost than ae2.0 for both MSTP
instances:



*test at EX8208_B> show spanning-tree interface *



*Spanning tree interface parameters for instance 0*



*Interface    Port ID    Designated      Designated         Port    State
Role*

*                         port ID        bridge ID          Cost*

*ae2.0            128:3        128:3  32768.80711f408e01      1000  FWD
ROOT *

*ge-20/0/1.0   128:1634     128:1634  32768.80711f408e01      1000  BLK
ALT  *



*Spanning tree interface parameters for instance 1*



*Interface    Port ID    Designated      Designated         Port    State
Role*

*                         port ID        bridge ID          Cost*

*ae2.0            128:3        128:3  32769.80711f41a801      1000  FWD
MSTR *

*ge-20/0/1.0   128:1634     128:1634  32769.80711f41a801      1000  BLK
ALT  *



*Spanning tree interface parameters for instance 2*



*Interface    Port ID    Designated      Designated         Port    State
Role*

*                         port ID        bridge ID          Cost*

*ae2.0            240:3        240:3  32770.80711f41a801     1000  FWD
MSTR *

*ge-20/0/1.0   128:1634     128:1634  32770.80711f41a801      1000  BLK
ALT  *



I would like to have ae2.0 blocked in instance 1 and ge-20/0/1.0 blocked in
instance 2. That's why I modify the cost of ae2.0 interface within instance
1 in both switches:



*msti 1 {*

*    vlan [ VLAN_200 VLAN_201 VLAN_210 VLAN_312 ];*

*      interface ge-20/0/1.0 {*

*        cost 1000;*

*    }*

*    interface ae2.0 {*

*        cost 10000;*

*    }*

*}*

However, nothing happens in terms of blocked or forwarding ports within
instance 1 after the change.



*test at EX8208_B# run show spanning-tree interface *



*Spanning tree interface parameters for instance 0*



*Interface    Port ID    Designated      Designated         Port    State
Role*

*                         port ID        bridge ID          Cost*

*ae2.0            128:3        128:3  32768.80711f408e01      1000  FWD
ROOT *

*ge-20/0/1.0   128:1634     128:1634  32768.80711f408e01      1000  BLK
ALT  *



*Spanning tree interface parameters for instance 1*



*Interface    Port ID    Designated      Designated         Port    State
Role*

*                         port ID        bridge ID          Cost*

*ae2.0            128:3        128:3  32769.80711f41a801     10000  FWD
  MSTR *

*ge-20/0/1.0   128:1634     128:1634  32769.80711f41a801      1000  BLK
ALT  *



*Spanning tree interface parameters for instance 2*



*Interface    Port ID    Designated      Designated         Port    State
Role*

*                         port ID        bridge ID          Cost*

*ae2.0            128:3        128:3  32770.80711f41a801      1000  FWD
MSTR *

*ge-20/0/1.0   128:1634     128:1634  32770.80711f41a801      1000  BLK
ALT  *



I also tried to increase ae2.0's priority, but it didn't have any impact in
interface ae2.0, either.



Could you, please, help me to discover what I'm doing wrong?


Thanks in advance


Kind regards


Octavio