STP Loop Guard

Unanswered Question
Jun 25th, 2009

Hi,

What is the effect of configuring loop guard globaly rather than on per port basis.

I have this problem too.
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Giuseppe Larosa Thu, 06/25/2009 - 23:41

Hello Roselyn,

having STP loop guard enabled on user ports is not useful the right tool for them is BPDU guard combined with portfast.

We have loop guard enabled on uplink ports on both sides and also on the bundle between the two distribution switches.

We combine it with broadcast storm-control set at 1%.

Enabling loop guard on user ports is not useful because it looks for the following event:

missing BPDUs from designated port on segment and moves the port to loop incosistent state instead of moving it to forwarding state.

So on user ports loop guard action is never triggered because the user port is the designated port on the segment by definition.

on user port is useful BPDU guard that looks for the following event:

if a BPDU is heard on the port the feature reacts by putting the port in errordisable.

This happens when users carry consumer switches on the job we use it and it is very effective

Hope to help

Giuseppe

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