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MST : fine tuning to prioritize some VLAN

 
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cedimp
Advisor

MST : fine tuning to prioritize some VLAN

Hi,

For better understanding i attached a diagram of how switches are connected.

You can see two rooms, two switches per room.

Switches into the same room are uplinked via copper (Trk1&3)

Switches between room are uplinked using fiber (Trk2&4)

Trk1&2 should be use only (or prefer) vlan 10

Trk3&4 should be use only (or prefer) other vlan

Bellow is the conf of the switch 1, with info of what change for switches 2,3,4 (only usefull part of it !)

 

 

trunk 7-8 trk1 lacp
trunk 25-26 trk2 lacp
trunk 23-24 trk3 lacp
trunk 27-28 trk4 lacp

spanning-tree
spanning-tree Trk1 priority 4
spanning-tree Trk2 priority 4
spanning-tree Trk3 priority 4
spanning-tree Trk4 priority 4
spanning-tree config-name "stpconfig"
spanning-tree config-revision 1
spanning-tree instance 1 vlan 10
spanning-tree instance 1 priority 1 (priority 2 for switch 2, 3 for 3, 4 for 4)
spanning-tree instance 1 Trk1 priority 1
spanning-tree instance 1 Trk2 priority 1
spanning-tree instance 1 Trk3 path-cost 100000000 (to be sure that trk1&2 will be prefered)
spanning-tree instance 1 Trk3 priority 4
spanning-tree instance 1 Trk4 path-cost 100000000
spanning-tree instance 1 Trk4 priority 4
spanning-tree instance 2 vlan 1-9 11-1999
spanning-tree instance 2 priority 1 (priority 2 for switch 2, 3 for 3, 4 for 4)
spanning-tree instance 2 Trk1 path-cost 100000000
spanning-tree instance 2 Trk1 priority 4
spanning-tree instance 2 Trk2 path-cost 100000000
spanning-tree instance 2 Trk2 priority 4
spanning-tree instance 2 Trk3 priority 1
spanning-tree instance 2 Trk4 priority 1
spanning-tree priority 1 (priority 2 for switch 2, 3 for 3, 4 for 4)

 

So far things seems not so bad, but i've some worry reading "show spanning-tree instance 1&2" command

I'll only paste useful info, not all

HP-2530-24G-SW1(config)# sh spanning-tree instance 1

 MST Instance Information

  Instance ID : 1
  Mapped VLANs : 10
  Switch Priority         : 4096

  Topology Change Count   : 204
  Time Since Last Change  : 45 mins

  Regional Root MAC Address : 5820b1-2e4900
  Regional Root Priority    : 4096
  Regional Root Path Cost   : 0
  Regional Root Port        : This switch is root
  Remaining Hops            : 20

                                                             Designated
  Port  Type      Cost      Priority Role       State        Bridge
  ----- --------- --------- -------- ---------- ------------ --------------
 
  Trk1            20000     16       Designated Forwarding   5820b1-2e4900
  Trk2            20000     16       Designated Forwarding   5820b1-2e4900
  Trk3            100000000 64       Designated Forwarding   5820b1-2e4900
  Trk4            100000000 64       Designated Forwarding   5820b1-2e4900

Here my problem is about all being in "designated forwarding" state

OK for Trk1&2 this is the wanted behaviour.

But Trk3&4 are also in the same state (with lower bad priority and path-cost) -> does it mean that switch will use this path also ? Or just only if Trk1&2 "dies" ??

Obviously same thing (symetric) for instance 2 :

HP-2530-24G-SW1(config)# sh spanning-tree instance 2

 MST Instance Information

  Instance ID : 2
  Mapped VLANs : 1-9,11-1999
  Switch Priority         : 4096

  Topology Change Count   : 197
  Time Since Last Change  : 46 mins

  Regional Root MAC Address : 5820b1-2e4900
  Regional Root Priority    : 4096
  Regional Root Path Cost   : 0
  Regional Root Port        : This switch is root
  Remaining Hops            : 20

                                                             Designated
  Port  Type      Cost      Priority Role       State        Bridge
  ----- --------- --------- -------- ---------- ------------ --------------

  Trk1            100000000 64       Designated Forwarding   5820b1-2e4900
  Trk2            100000000 64       Designated Forwarding   5820b1-2e4900
  Trk3            20000     16       Designated Forwarding   5820b1-2e4900
  Trk4            20000     16       Designated Forwarding   5820b1-2e4900

I won't go further not to loose you but just see bellow for switch 2 :

HP-2530-24G-SW2(config)# sh spanning-tree instance 1

 MST Instance Information

  Instance ID : 1
  Mapped VLANs : 10
  Switch Priority         : 8192

  Topology Change Count   : 101
  Time Since Last Change  : 46 mins

  Regional Root MAC Address : 5820b1-2e4900
  Regional Root Priority    : 4096
  Regional Root Path Cost   : 20000
  Regional Root Port        : Trk1
  Remaining Hops            : 19

                                                             Designated
  Port  Type      Cost      Priority Role       State        Bridge
  ----- --------- --------- -------- ---------- ------------ --------------
 
  Trk1            20000     16       Root       Forwarding   5820b1-2e4900
  Trk2            20000     16       Designated Forwarding   480fcf-931840
  Trk3            100000000 64       Alternate  Blocking     5820b1-2e4900
  Trk4            100000000 64       Designated Forwarding   480fcf-931840

Trk3 blocked :ok, but trk4 still "designated forwarding"

 

Thanks for your help, do not hesitate to ask me some more info/debug/diagram

 

Edit : i have done something that seem to explain.

For each switch i did a "sh spanning-tree instance 1 & 2" and then report results (designated, root, alternate, blocking, forwading, ...) on my diagram and then it seems that for trk 1 & 2 (for vlan 10) each time there is a designated/forwarding port for instance 2 the port at the next hop has an alternate/blocking state, then instance 2 is not using trk 1 & 2 unless it will have no other way !

Same think apply to trk 3&4 with instance 1.

It seems that i hav what i want : in normal use trk1&2 will forward vlan 10 only, trk3&4 the others ones.

Do you confirm ?

thanks

4 REPLIES 4
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Vince-Whirlwind
Honored Contributor

Re: MST : fine tuning to prioritize some VLAN

I would stop using instance 1.

Put VLAN10 on instance 3 and check the difference.

Generally I'm not a fan of sacrificing redundancy and space for peaking bandwidth to separate VLANs like this, so I don't have much practice with it.

Highlighted
cedimp
Advisor

Re: MST : fine tuning to prioritize some VLAN

Hi Vince,

sorry but i do not understand :  on my config instance 1 is dedicated to vlan 10. Why would i use a new instance (3) and put vlan 10 on it ? That wouldn't change anything... to me that will be the same thing. Instance 1 is a separate instance not the internal (default) instance.

Thanks

16again
Respected Contributor
Solution

Re: MST : fine tuning to prioritize some VLAN

Your config is OK.
SW1 is the root switch, so all of its ports will be forwarding for all VLANs.
And now rethink on which ports SW1 will learn MAC addresses:  Only on ports where the remote isn't in blocking state !
So SW1 will never send  out unicast on ports where remote side is in blocking state.  So blocking on one side  effectively makes other side also non-operational.

re-read at will ;-)

Highlighted
cedimp
Advisor

Re: MST : fine tuning to prioritize some VLAN

Yes this is what i understood ! In fact on my diagram i did some drawing to "see" on each trunk how was each instance (root, forward, block,...) and then this is easy to see and realize that all is good !

 

Once again thanks for your help !