If a port configured for portfast status receives any bpdu, that port looses its portfast status and behaves like a standard spanning-tree port. If that port happens to be configured for bpdu guard, this operation is not allowed. In that case the port is moved to err-disabled and traffic is dropped. You cannot enable bpdu guard without portfast.
Here i have little confusion.
By default portfast is not disabled on port when switch receives BPDU on portfast enabled port. We use bpdufilter feature to disable portfast on particular port on receiving BPDU.
Bpduguard can be enabled without portfast feature also and it will disable the port on receiving BPDU, does not matter with portfast or without portfast.
Please let me know if i am wrong.
Paul is correct ; If a port configured for portfast status receives any bpdu, that port looses its portfast status and behaves like a standard spanning-tree port. It might go thru 4 stages: from blocking to forwarding or stop at blocking.
For extra protection, we have bpdu guard, which will put port into err-disabled.
you can do test in GNS3 with switch module; I saw some weird stuff when doing it on different switches a while ago.
if you connect another switch to portfast port, port should end up talking with new switch.
look at my results in https://learningnetwork.cisco.com/docs/DOC-13582
others have also post some summaries (see More Like This) or https://learningnetwork.cisco.com/message/174919#174919
Message was edited by: Martin