- Bronze, 100 points or more
I have a question about bddu filter feature.
According to cisco press book ccnp bcmsn by David hucaby,stp still runs on portfast-enabled port.All portfast-enabled ports have bpdu filter feature automatcically configured.
Then in the very same book i find"
Bpdu is used to disable stp on port basis"
My point is portfast-enabled ports have stp running and bpdu filter option automatically on .Bpdu filter is used to disabled stp on port basis. So it could be deduced from the above "stp is not running on portfast-enabled port because of bpdu filter feature".Am i correct?
This is not correct. You can enable portfast without bpduguard.
Bpduguard can be configured in two different way:
- globally, in config mode. It then applies to all portfast ports (with operational state "on" as I mentioned earlier).
- at the interface level. In that case, it is entirely independent from portfast.
This is what you find in the cisco doc
Understanding How PortFast BPDU Filtering Works
BPDU filtering allows you to avoid transmitting BPDUs on PortFast-enabled ports that are connected to an end system. When you enable PortFast on the switch, spanning tree places ports in the forwarding state immediately, instead of going through the listening, learning, and forwarding states.
By default, spanning tree sends BPDUs from all ports regardless of whether PortFast is enabled. BDPU filtering is on a per-switch basis; after you enable BPDU filtering, it applies to all PortFast-enabled ports on the switch.
This goes with what I thought was the default but there has been so much change with spanning tree now that cisco does RST. I wouldn't be surprised if it works different on different models of switches but I have not seen a cisco document that says BPDU filter is on by default.