MSTP - 2 Links between 2 2810

[Björn Bechtold]

Hi,

i've got a Problem get MSTP to work like i want.

My Situation:
I've two 2810-24G Switches. And between this switches 2 microwave radio relay links. And there are 2 Vlans that should be transfered over the microwave radio relay. Each Vlan over an own Link

2 Links

Link1 Vlan1 & Backup for Vlan 2
2810============================= 2810
Link2 Vlan2 & Backup for Vlan1

Now my Problem:
I've configured on both Switches 2 vlans ID: 1,2. On both switches i set 2 Ports to "Tagged" ( 13 + 15 ) and connect the two Ports.
i also configured the MSTP:

on Switch 1
spanning-tree config-name RiFu
spanning-tree config-revision 1
spanning-tree instance 1 vlan 1
spanning-tree instance 2 vlan 2
(enabling spanning-tree)
spanning-tree instance 1 priority 1
spanning-tree instance 2 priority 0
spanning-tree priority 1

on Switch 2
spanning-tree config-name RiFu
spanning-tree config-revision 1
spanning-tree instance 1 vlan 1
spanning-tree instance 2 vlan 2
(enabling spanning-tree)
spanning-tree instance 1 priority 0
spanning-tree instance 2 priority 1
spanning-tree priority 0

When i Connect the 2 Links (Ports 13+15) the MSTP begin to Act and enabling the connection between the Switches. And after a few seconds the Link becomes active and I can Ping the other Side.
But both Vlans connecting over the same Link (Link 1 Port 13), what I want is that each Vlan connect over another Link.
Vlan 1 over port 13 Link 1
Vlan 2 over port 15 Link 2

How can I tell the Instance 1 to use Port 13 and Instance 2 to use Port 15 ?

Now this Forum is my last chance. I try to get the two Switches to work since 2 days now.
Thanks a lot.

B.Bechtold

[Michael_Breuer · Accepted solution]

Hello Björn,

basically you have the following options:

1) Assign different cost values for each instance. i.e. try to make the redundant path worse than the primary:

if the normal path cost is 20000 (for a gigabit link), then assign let's say 21000 to the second link:

spanning-tree instance 1 13 path-cost 21000
spanning-tree instance 2 15 path-cost 21000

2) Set up a LACP Trunk between the two switches by aggregating port 13 and 15 to a logical trunk interface. Then the trunking process will take about load balancing.

On both ends you need the following config:

trunk trk1 13,15 LACP
vlan 1
tagged trk1
vlan 2
tagged trk2


Cheers,

Michael

[Björn Bechtold]

Hi Michael,

Thank you for your quick answer.

I Will test your first option with the Path costs

sadly your second Option is not acceptable because the two links / Vlans belongs to two different Companys which would have both their dedicated Link.
This was also my first idea. But when i simply trunk the two links no Company has ists "own" link.

I will test ...

Thanks

Bjoern

[Björn Bechtold]

Hi Michael,

Thank You very much for your Help.
The Option to set the Path Cost was the solution.

on Switch 1
spanning-tree instance 1 13 path-cost 21000

On Switch 2
spanning-tree instance 2 15 path-cost 21000

Now the 2 MSTP-Links are on 2 physical Ports 13 & 15.

The Failover Function is already working. When one Link crashes down MSTP is switching over to the active Link.

Thanks

Björn