I know the topic bpdufilter had been discussed many times in the forum but it looks to me none of the topics talked about whether it really works as stated in the cisco documents (or maybe I didn't find the right topic?). anyways here's my question.
First, I understand what was supposed to happen according to cisco press, that "If a BPDU is received on a Port Fast-enabled interface, the interface loses its Port Fast-operational status, and BPDU filtering is disabled.". However, somehow I couldn't see the effect after the following configuration steps. Here's what I did:
platform: 2*3550 switches, topology:
| sw1 |----------------------------------|sw2 |
the port fe0/3 on both switches are access mode vlan 1. sw2 is the root bridge for vlan 1.
both sw1 and sw2 have"spanning-tree portfast enable"
at this point I "show spanning-tree int f0/3 detail" and saw bpdu received increasingly. I then unpluged the cable between sw1 and sw2 from f0/3 on sw1.
Then I had only sw1 configured"spanning-tree portfast bpdufilter default". Now, according to the document, when I plug the cable between the switches back into the port f0/3 on sw1, the port should receive BPDU from sw2, and therefore "loses its Port Fast-operational status, and BPDU filtering is disabled". The former also implies that the port should start the normal STP process, meaning going through "listening" "learning"...etc, after 30s, the port goes into forwarding, right?
NO. The port went immediately into forwarding right after I plugged the cable back in."show spanning-tree int f0/3" didn't see any lsn, lrn status. The portfast operation looked still working. What went wrong?
I believe that there was something wrong in my testing above, however I couldn't figure that out. Could some one please help me here?
Thanks a lot!