Trunking FortiSwitch to Cisco Switch

[dancarlton]

Having issues connecting 2 Cisco Switches to standalone managed FortiSwitches.

See diagram below.

The Cisco switches are running rapid-pvst.

When we connect these up, the ports go into error-disabled.

I believe we are running into STP issues because the FortiSwitches are using MST. I tried to configure rpvst-port on the mclag interface to the Cisco switches, but since we are using way more than 16 VLANs, you cannot.

Any insight into getting this connectivity to function would be appreciated.

[Anonymous]

Hello,

As per the query you have addressed you can use the link mentioned below 

Inter-operability with rapid Per-VLAN Spanning Tree plus (PVST+) can be enabled per port on managed FortiSwitch devices. It is disabled by default.

https://docs.fortinet.com/document/fortigate/6.4.0/new-features/499186/inter-operability-with-per-in...

https://docs.fortinet.com/document/fortiswitch/7.0.1/administration-guide/364618/support-for-interop...

[fp1]

Be aware of the limit of  the ussage of 15 Vlans + Native Vlan (untagged) if you are configure interoperabity to Pvst+. 

e.g. 

   edit "port3"
                set rpvst-port enable

We are working at the same issue with MST. It is not possible to configure the default (Region name = NULL and Revsion number=0) at Cisco side. At fortinet side, it is  not possible to set vlan-range at instance 0 !!!! Try to define a new region name with a new revison number. Think about to create 2 Instances analog to Fortigate Defaults (Instance 0 = Vlan 1-4093 and Instance 15 = Vlan 4093). Hope thats help you. Be aware that regio name and revision number have to be the same, between Cisco and Fortigate. 

Also to discuss: MST Configuration Digest - is the algorithm the same between Cisco and Fortigate ? How knows.

config switch stp instance
edit "0"

!  set vlan-range ! not possible

config switch stp instance
edit "15"

set vlan-range 4094

set vlan-range
<vlan_map> single vlans or ranges of vlans separated by commas(no whitespace)
e.g. 1,3-4,6,7,9-100
The vlan_map configuration entered must be less than 4096 characters.