MSTP Instance Inquiry

Answered Question
Jul 14th, 2008

Hi! I have these scenario below:

instance 1

vlan 10-15

instance 2

vlan 16-20

R1

instance 1 active

instance 2 standby

R2

instance 1 standby

instance 2 active

What will be the effect in instance 0? How should r1 and r2 be configured? If I add new vlans in instance 2 (say vlan 30-35), what configuration should I do in instance 1 (if there is any)?

I have this problem too.
0 votes
Correct Answer by n.nandrekar about 8 years 6 months ago

hi!

As I mentioned before, the addition of the vlans will not change the topology in the instances. The ports R1 and R2 will still remain the root posts for those instances as long as you donot change any parameters like priority/ cost/ port priority etc for those instances.

Regards,

Niranjan

(pls rate helpful posts)

Correct Answer by n.nandrekar about 8 years 6 months ago

Hi!

All the active vlans which have not explicitly been assigned to a particular instance will be a part of instance 0. there is no need to configure anything specific on instance 0 unless you want to engineer the traffic to take a specific path. The default values of that instance will be used to decide on the root bridge and the designated/root/blocked ports.

When you add more vlans to 1 instance, there is no config cchange that you have to do on other instances ( or even in the same instance as a matter of fact).

In brief : on each switch, every MSTP instance has some default valies for parameters like bridge-priority, port cost, port priority etc. The topology is formed according to these values. You can change these values for a particular instance so that a single port is blocking for that instance but forwarding for other..... or a bridge is root for 1 instance and non-root for other.

When you add vlans to the instance, there is no change in the topology or other instances. The traffic for those vlans will follow the liks that are in fwd state according to that instance.

Hope this is helpful. Please rate if it is.

Regards,

Niranjan

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 4 (2 ratings)
Loading.
Correct Answer
n.nandrekar Mon, 07/14/2008 - 23:20

Hi!

All the active vlans which have not explicitly been assigned to a particular instance will be a part of instance 0. there is no need to configure anything specific on instance 0 unless you want to engineer the traffic to take a specific path. The default values of that instance will be used to decide on the root bridge and the designated/root/blocked ports.

When you add more vlans to 1 instance, there is no config cchange that you have to do on other instances ( or even in the same instance as a matter of fact).

In brief : on each switch, every MSTP instance has some default valies for parameters like bridge-priority, port cost, port priority etc. The topology is formed according to these values. You can change these values for a particular instance so that a single port is blocking for that instance but forwarding for other..... or a bridge is root for 1 instance and non-root for other.

When you add vlans to the instance, there is no change in the topology or other instances. The traffic for those vlans will follow the liks that are in fwd state according to that instance.

Hope this is helpful. Please rate if it is.

Regards,

Niranjan

jerome_benzon Mon, 07/14/2008 - 23:37

Hi! Thanks for the great reply. However, what if r1 and r2 are just root port for an instance. r1 and r2 on these matter has a client which is the root bridge. Thanks.

Correct Answer
n.nandrekar Tue, 07/15/2008 - 00:06

hi!

As I mentioned before, the addition of the vlans will not change the topology in the instances. The ports R1 and R2 will still remain the root posts for those instances as long as you donot change any parameters like priority/ cost/ port priority etc for those instances.

Regards,

Niranjan

(pls rate helpful posts)

Actions

This Discussion