Spanning Tree and VLAN with c3650

Unanswered Question
Jun 1st, 2009


I would like some help on configuring two C3650 for spanning tree between two VLAN.

Here is the goal :

Having two operator LAN to LAN connections between two Data Centers to have some redundancy.

For connecting the two data centers with each other, we have two C3560 (one on each side).

We would like to allocate a vlan of at least 8 ports for each connection and have spanning tree for being able to switch on the other connection if one was down...

Is this possible ?

Can you give me some info about the possible configs ?

Best Regards,


I have this problem too.
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Jon Marshall Mon, 06/01/2009 - 08:52


If i understand correctly you have a switch at either end and you want to use 8 ports on each switch for the connection. If so you would be better creating an etherchannel between the 2 switches and then STP will see the etherchannel as one link and will not block -


BrinksArgentina Mon, 06/01/2009 - 09:57

In the doc posted by Jon, you can see that 8 is the maximun active ports, but you can do load balancing forcing STP to elect one port as root port for some VLANs and the other for the rest.

This is an example

</p><p>spanning-tree mode rapid-pvst</p><p></p><p>interface range GigabitEthernet1/0/1 -8</p><p> description ECh_A</p><p> switchport trunk encapsulation dot1q</p><p> switchport mode trunk</p><p> channel-protocol lacp</p><p> channel-group 1 mode active</p><p> spanning-tree vlan 20,21,22 port-priority 16</p><p></p><p>interface range GigabitEthernet1/0/9 - 17</p><p> description ECh_B</p><p> switchport trunk encapsulation dot1q</p><p> switchport mode trunk</p><p> channel-protocol lacp</p><p> channel-group 2 mode active</p><p> spanning-tree vlan 23-25 port-priority 16</p><p>

spanning-tree vlan vlan-id port-priority priority

For priority, the range is 0 to 240, in increments of 16; the default is 128.

All other values are rejected. The lower the number, the higher the priority.


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capmedia Tue, 06/02/2009 - 05:13

Hi Jon,

It seems that you haven't completely understood, maybe I haven't explicated very well... :)

BUT the Etherchannel is responding to my problem anyway.

At first we had the idea not to use an etherchannel but something like 2 virtual switches inside the C3560 at each site which are connected with two operator LAN to LAN...

We are currently using only one switch where we should use two to be fully redundant (even at hardware level).

Since we have only one switch the etherchannel solution is as good as using virtual switching for us.

Thank you very much.

Best Regards.



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