[c-nsp] MSTP issue. Isolation of core switch

[cnsp at marenda.net]

On Wed, Jan 09, 2013 at 06:41:34PM +0200, Andrey Teslenko wrote:
> Hello!
> We have a large L2 network with one MSTI region and few ring topologies.
> 
> The topology looks like this:
[...]
> It all started after the closure 10G ring.
> 
> In general periodically from all sides sw-Core sees 'BPDU received 0'.
> 
> Neighbors in the 0-th (CST) instance sees the packages, but in the 1-st
> (operating) no.
> 
> After that  they put the ports into position 'blk disput'.
> It is understandable, because sw-core does not see BPDU from them, so it
> can not answer.
> 
> Here is configuration of MSTP
> 
> spanning-tree mode mst
> spanning-tree logging
> spanning-tree extend system-id
> !
> spanning-tree mst configuration
>  instance 1 vlan 1-4094


Give it a Name and a Revision Number.
dont forget to ACTIVATE the new revision !

On All switches identical mst configuration
(name, revision, mapping).

Remember you may need to reload after a wr mem to change
spanning tree version/mode.


> *show spanning-tree mst*
> 
> ##### MST0   vlans mapped:   none

[...]

You wont see here anything since all your vlans have been mapped to
instance 1, not to instance 0 .


For Example:

!
spanning-tree mode mst
spanning-tree logging
spanning-tree portfast default
spanning-tree portfast bpduguard default
spanning-tree extend system-id
!
spanning-tree mst configuration
 name MAGIC
  revision 2
  instance 1 vlan 500,600,900
  instance 2 vlan 501-599
  instance 3 vlan 700-799
  instance 4 vlan 100
  instance 5 vlan 800-899
  instance 6 vlan 601-699
  !
! all other vlans will be in instance 0
  !
 spanning-tree mst 2-3 priority 28672
 spanning-tree mst 5 priority 24576
!

Maybe that vtp version 3 (on cisco) helps you in distributing the instance mapping.

You may want to set the priorities to ensure which switch is your primary and second root,
else they will elect /compute on an fancy mac-adress iand interface speed based algorithm.

So do this explicite for each instance.

Remember that some Vendors Switches need to have the vlans created
(or will do it for you exceeding capabilities)
and others not.


... and iff you have cisco switches powerfull enought,
run per-vlan (rapid) spanning tree. This prevents you from getting a knot in the head
and a lot of fun debugging mst.

Hope this help's,

Juergen.