[c-nsp] spantree pvst and mst

[Shaun]

I have a c3750 with many c2950G's connected to it.  The 3750 has 2 uplinks 
to each of my providers core routers.  The 3750 does BGP with my provider 
also.  The original plan was to have another 3750 and the uplink's from go 
into each of them (1 uplink into 1 3750 and 1 into the other).  Right now I 
just dump both of them into the one 3750, I set both ports to access and 
assigned them vlan 20 which has the /29 assigned to it from my provider.

The original problem is that I have too many vlans for the 2950 and I run 
into spanning tree interface limit problems.  For whatever reason vtp 
pruning is not doing it's job and I have yet to find anybody who can tell me 
why it's not working or with a answer on how to fix it.  The solution for 
now is to change from pvst to mst on the 2950's but leave the 3750 on pvst.

I setup a test network using a spare 3750, 3550, and 2950 added 100 vlans 
just to test, when I set the 2950 and 3550 to mst everything appears to work 
fine...  When I do this on my live network the 2950 and all customers on it 
are no longer accessible.  The logs show this error.

Jan 15 16:59:53 PST: %SPANTREE-2-PVSTSIM_FAIL: Superior PVST BPDU received 
on VLAN 20 port Fa0/1, claiming root 8191:00d0.00ec.b47c. Invoking root 
guard to block the port
Jan 15 16:59:53 PST: %SPANTREE-2-ROOTGUARD_BLOCK: Root guard blocking port 
FastEthernet0/1 on MST00.

Again vlan 20 is vlan I used to assign my provders /29 and it's assigned to 
both fa1/0/1 (uplink1) and fa1/0/2(uplink2) on the 3750.  From what I can 
tell spanning tree is disabling port fa0/1 on the 2950 because it see's a 
loop on vlan20, but fa1/0 is a trunk and has many vlans on it.

I even tried unplugging fa1/0/2 on the 3750 to see that would correct the 
problem but it did not.  I also did no span vlan 20 on the 2950, no change 
either.

Any suggestions?

-- 

~Shaun