Using MSTP like I used RSTP

[J Vesterdahl]

Hello all.

A while ago I asked why the edge-port commands of my 2824 switches had changed with firmware version I.10.43.
It turned out that RSTP had been replaced with MSTP to comply with the latest standards, and a new feature - auto edge detection - was added.
Since MSTP is backwards compatible with RSTP and all my switches were set to use RSTP, my network did not show any signs of change.
Now I've enabled MSTP in my redundant ring, and I need some reassurance ...

My network is almost completely static with no users logging on and off all the time. It is basically a transport medium for telemetry, video etc., each functionality placed into its own VLAN.
Only one VLAN - the management VLAN has IP numbers, because I don't need routing between VLANs.
In RSTP, the root was easily set, but MSTP uses multiple types of roots, which confuses me slightly:

- The CST root looks like the equivalent to the one and only root in RSTP. All the switches agree that this is indeed the CST root. This setup will handle the spanning tree operation like RSTP does, right?

- Each and every switch in the ring considers itself the IST regional root. I have not set the spanning tree config parameters, so this is expected behavior. At this time I do not need multiple STP instances, so I should not worry about this, since the CST will take care of the reconfiguration for me, right?

Everything seems to work, I am just looking for reassurance that I am doing things right.

[RicN]

>Each and every switch in the ring considers
>itself the IST regional root. I have not
>set the spanning tree config parameters, so
>this is expected behavior. At this time I
>do not need multiple STP instances, so I
>should not worry about this, since the CST
>will take care of the reconfiguration for
>me, right?

I thinks the reason for every switch being its own IST regional root is because you have not set a common region name across all switches. Then each switch is its own MSTP region and has its own IST.

(The default MSTP configuration name is the MAC address if I am incorrect, and by that different regions.)

If you set a common configuration name for all MSTP switches then you would have a common IST for all VLANs that is not included in any MSTP instance.

[J Vesterdahl]

Yes, but do I need to, or can I just leave the ISTs as they are?
All I want is one big spanning tree, and the CST should take care of that, right?

[RicN · Accepted solution]

I think that CST "sees" every MSTP-region as one switch (even if it is many devices) and in your case that is just what you do have.

So I think you could leave it that way and just use the CST.

[J Vesterdahl]

Oh - nice way of looking at MSTP!
A spanning tree of spanning trees! That makes sense to me.
Any other thoughts, anyone?