From: ismail el-shalh (ishelh_mdsa@yahoo.com)
Date: Fri Apr 20 2007 - 23:19:41 ART
Here is my opinion to your case:
Enabling portfast means that you are skipping listening and learning
process, hence you are exposed to form a loop if you received a BPDU, this
means that you should switch your port to go back through the STP process. the
thought process is to disable BPDU filtering so the port can switch back to the
traditional STP to help in determining the characteristic of this BPDU to go
through the four STP steps election process.
If you want to continue enable the BPDU filtering and yet the port should skip
STP process then try to disable the spanning tree for that specific VLAN and
enable the BPDU filtering on the port, by doing this the IOS will not apply the
logic of reverting the port back to the STP and yet you are enabling portfast
from another view.
What you are trying to accomplish is to change Cisco thought process and customize
it according to your need, still you have the option to enable pbduguard, but
as you know the action here will put your port in the err-disable.
Thanks
Ismail El-Shalh
----- Original Message ----
From: WorkerBee <ciscobee@gmail.com>
To: Cisco certification <ccielab@groupstudy.com>
Sent: Saturday, April 21, 2007 4:23:46 AM
Subject: BPDU Filtering and PortFast Relationship
Hi Group,
This is something that confused me.
If "BPDU filtering" + "Port Fast" is enabled globally, why does a switchport
loses it's Port Fast status as well as BPDU filtering when a BPDU
packet is received from that particular port?
If I want BPDU filtering protection and Port Fast status of a switch
port, why upon
receiving a BPDU from a PortFast port turned off both features?
So how can I ensure I still have PortFast enable and BPDU filtering
just block the BPDU packets from the PortFast port and yet has both
features enable without losing their status?
Reference link,
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3560/12235se/cr/cli3.htm#wp1946892
You should globally enable BPDU filtering on a switch so that hosts
connected to switch interfaces do not receive BPDUs. If a BPDU is
received on a Port Fast-enabled interface, the interface loses its
Port Fast-operational status and BPDU filtering is disabled.
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