Tom,

I remember our conversation a few weeks ago. I did not get a chance to have a go at MSTP, mainly because I have no expierence with it, and looking at the configuration properities, it looks a little daunting.

It has also been a very busy few weeks with the deployment of 200+ phones across several sites, and the system is functioning great with out the LAG trunk, I am just trying to plan for the future.

I made a few postings a few weeks ago, one here and one on the Cisco forums on reddit, and a user there gave me some advice I have been unable to make work (I think it's just wrong), but I would love to go this route if it is in fact possible.

Here is the thread : http://www.reddit.com/r/Cisco/comments/x91tc/vlan_trunks_spanning_tree_and_a_port_blocked/c5kskch

This user implies it's possible to block a VLAN across the LAG which would end the logical loop problems.

It looks like his advice is to make the LAG into a trunk, and then block specific VLAN's from transiting it, but in trunk mode, I can't assign it an IP, so I am sorta wondering how exactly you transport packets across it.

Can you confirm that his advice is in fact incorrect?

If MSTP is my only route, then I suppose it's time to dig into the docs and see If I cant get it up and running.

Tom,

Thanks for all your help.

I guess it's time to have a look at MSTP and see if I cant get this up and running before these go into production.

I really appreciate your advice!

Ok so a quick question here.

It doesnt appear my cisco 890 supports MSTP.

But both switches do.

How exactly do I go about this?

Basically vlan 10 needs to be available on both switch's uplink ports but not on the LAG, vlan 20 and 30 need to be available on the LAG but not on the uplinks.

So put both switches in the same region and give every vlan its own instance?

Hi John,

Reference my picture below. The vlan 10 instance picture, shows how your network normally would look. Obviously the ports will go down.

The vlan 20/30 instance picture, notice the links between the left switch and right switch.  The router is sort of a wild card. I don't know how it will behave but with the switch configuration if you make each vlan their own instance and configure as my diagram, it should work, provided the router won't hose you up.

-Tom

Two questions,

Why the U vlan 1? We basically have that shut down.

For the 20/30 instance. I need 10 on the firewall uplink (so it can route out).

Otherwise this looks pretty simple.

Got it, thanks again.

6PM PST tonight this goes into play and we will see if it flys with the router!

Appreciate all your help, if you're ever in San Diego, I owe ya a beer!

edit.. Just for clarity, both switches go in the same region with teh same revision # ?

The MSTP revision levels should be the same on all devices. The MSTP region must also be the same as the switches only support 1 region.

-Tom