I have a triangle topology of 2 cisco + other switch :
2 cisco are configured as mstp with vlan 10 on instance 1
the other switch is configured rstp
the problem is that i get 2 root in the topology
and the also when i change teh priority of the other switch nothing is changed
Is there a specific config to support the cisco both for mstp in one port and rstp on the other one ?
can anybody suggest me a solution
You're not giving me enough information to answer for sure, but I think you've been hit by the "sync" mechanism, which is common to RSTP and MST.
During its reconvergence, those protocols might have to sync the non-edge ports in order to prevent transient loops. Designated port connected to a peer RSTP or MST bridge send a proposal and quickly gets back an agreement. If a port is edge (i.e. configured for portfast), it is connected to a host and cannot introduce a loop, so it is not synced.
The problem is that if a port is edge but not configured as such, it is blocked by the sync and takes 30 seconds to come back to forwarding. With RSTP and MST, it is thus very important to make the proper "portfast" configuration on the port leading to hosts. That's what I was alluding to at the end of my previous answer, as I did not know exactly what kind of behavior you observed. I guess you were doing some form of ping from a host connected on a port that did not have portfast configured on it. In that case, it is perfectly expect to have 30 seconds of traffic interruption.
If this was not the case, then please come back with additional information. The vlan to instance mapping, RSTP or MST should be irrelevant for the discussion;-)