As I understand it Portfast should prevent a switch from generating TC BPDUs when the port moves into the forwarding state. There is a feature on the lastest IOS versions that allows you to enable Portfast on Trunk links.
We are having a few issues at the moment with a few cascaded switches that cannot be point to point to the distribution layer due to lack of fibre. When these cascaded switches are powered off, upon rebooting the switch port moves into forwarding state (on both access switches), which generates multiple TCN BPDU's causing mac tables on all switches in the VLAN to flush their MAC tables. This causes our management platforms to temporarily raise alerts for reachability to multiple switches in this VLAN.
I was hoping to configure PORTFAST on these cascaded ports that keep going down / up, however, after testing it, the switches still gnerated TCN's and flood the VLAN.
Is this because the links to the cascaded switches are classed as P2P in Rapid PVST and cannot disable TCN generation ? Or is portfast not working on the trunk link ?