STP loop guard

Im a little bit confused of this command, could you clarify it for me:

Cisco CG says:
"to prevent alternate or root ports from becoming designated ports
because of a failure that leads to a unidirectional link."

But for example in Adv Tech WB 5.0 I've found:
"if one of these blocking links transitions to forwarding state
erroneously, a loop can occur (...) loop guard prevents this by
transitioning blocking ports into loop-inconsistent istead of rorwarding
if BPDUs topp being recived from the designated port."

Let's look at the following example.

We have 2 switches and one link between them, SW1 is the root, SW1 fa0/1
is DP, SW2 fa0/1 is RP, if unidirectional link exist for example SW2
will not able to receive BPDUs from SW1 it put this interface as DP
after 30 sec (by default).
If we use spanning-tree guard loop under SW2 fa0/2 interface will be
blocked.

                        (Tx) ------X------ (Rx)
ROOT SW1 SW2
(fa0/1 - Designated Port) (fa0/1-Root Port)
                        (Rx) ------------- (Tx)

Am I right?
Can you confirm if I can use it also on interfaces that are in blocking
state also like IE says?
Please let me know if I put this command on the right switch.

Thanks in advance!

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Received on Fri Apr 17 2009 - 19:12:15 ART