[c-nsp] MSTP +STP

[Andrew Fort]

Alexandra Alvarado wrote:
> Hello,
> 
> I'm new in MSTP, I need to use MSTP because we are going to use more than 128 vlans and STP is not enough,
> my question is: I need to make interact switches cisco and switches non cisco, in switches cisco I'll use MSTP 
> but in switches non cisco I need to use STP and pass some vlans.
> 

On the ciscos, the ports that connect to the non MSTP domain (i.e., the 
non cisco switches, or any other MSTP switch that does not have 
precisely matching VLAN->instance mapping configuration) will become a 
'boundary port'.  This is the 'edge' of the MSTP domain.  Thus, your 
edge ports to the other switches will become boundary ports.

> Is it posible???

Yes, we do this: i.e., at the edges of the network where MSTP has little 
real benefit (and is too difficult to manage without well synchronised 
automation ala CNS CE), we run a RSTP (802.1w) domain.  This could be an 
alternatively be an 802.1d domain, also, as you are attemting to do.

> Where I can find an example???

In your lab, most likely :/  Try reading and re-reading the Cisco 
documentation on MSTP.  It will stick eventually, I'm told :).

> I have read that if I want to comunicate vlans between MST and STP I need to use IST instance,
> in my case I need to use STP the range of vlans 201 to 300. Is it right???

Regular 802.1d STP doesn't know about VLANs at all.   It only knows 
about bridge ports, no matter what VLANs they may be carrying.  What 
VLANs are used on your non cisco switches is dependant on what VLAN 
forwarding configuration you have:  a) at the edge of the Cisco network 
(i.e., "switchport trunk allowed vlan <list>"), and b) in the 
configuration of your non-cisco switches.  (I've assumed that VLANs 
201-300 are also forwarded on the Cisco network).

The Ciscos will talk STP to the non-cisco switches (i.e., all but one of 
the ports into the non-cisco network will be blocked, if it forms 
loop(s) back to the cisco network), and they'll talk MSTP to its buddies.

If you do not need the load balancing that MSTP supports, I'd recommend 
Rapid STP, rather than Multi-instance STP - you then get the faster 
failover protection.  Some people on this list have (mutedly) reported 
problems with MSTP on lower end switches, and RSTP, being more like STP 
(in network design terms), is less complex and better understood (e.g. 
by your vendor if you lodge a support ticket).

However, you should just be able to configure this, and if you have 
matching "spanning-tree mst configuration" stanzas on your MSTP switches 
(and you have all the other pre-requisites configured, see the 
documentation), then your old school STP switches will just see the 
Ciscos as other switches in the STP.  Configure the Ciscos as primary 
and backup root bridge and that'll trickle down to the STP part of the 
network also.

Cheers,
Andrew