MSTP on Catalyst 9300 compatible with RSTP of other switchs

[Samsoum]

Hi, I have a Catalyst 9300 That i configured the MSTP Root brisge to zero as main switch and other switchs from other brands ( less then 20 switchs) have only RSTP on their configuration and all defaults bridge value 32768.

When i close the ring all up, when i breack the RING all the RSTP Ring goes up again immediatly with a goos redudancy laptime, only the Catalyst falls down the ping.

On the Catalyst 9300 we have many vlans ( thats why we put MST configuration)

Any suggestions of explanation  on why this is on?

All the switchs are brand new bty

THANKS TO ALL

[M02@rt37]

Hello @Samsoum 

Please, how the ports on C9300 facing the RSTP switches are configured ?

[Samsoum]

No idea about this, the engineer saying just that he configured all ports to be STP on C9300

I dont have an image to show you

[Jens Albrecht · Accepted solution]

Hello @Samsoum,

you mentioned that you use several switches from other vendors and this causes potential problems, especially since you appear to use multiple vendors beside Cisco.

The only STP protocol that Cisco implemented according to RFC standards is MSTP. Therefore, in a mixed multi-vendor environment it is always best practice to run MSTP on all switches, provided the other vendors do support it. So if possible use MSTP in your network on all switches and this should run smoothly without issues.

Cisco implemented STP as PVST+ and RSTP as RPVST+, meaning that they are implemented to run per-vlan using proprietary extensions to the standard protocols. Some vendors do support Cisco's per-vlan extensions, some only support the RFC-standard, while others use their own proprietary per-vlan extensions which are not compatible with Cisco's implementation.

So you need to check whether your other switches do either support MSTP (best solution) or at least support Cisco's per-vlan extensions. If the answer to both questions is "NO", then there is nothing you can do as the switches will not be able to communicate with the Cisco Cat9300.