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Re: 3550 root guard and loop guard posted 11/06/2002
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Root guard, is used to make sure the port will never become a root port. It works in such as way
that if the spanning tree calculation result on the port with the root guard configured selected as
the rootport (meaning a bpdu is received on this interface with higher bridge ID), the port is put
in incosistent state (read as blocked), and the spanning tree will select another port as the root

For loopguard, what it do is to make sure that your Root port and alternate will never become a
Designated port for "other" switch.
So in other words, your switch will never be the switch in the root path for others. Imagine if
you're on access switch and suddenly the uplink of the access switch became the Designated port of
the distribution switch, something must be wrong. Use loopguard to prevent this from happening.

That is my understanding, perhaps other can give more.

                      "Szeto Jeff"                                                                                                     
                      <jytszeto@xxxxxxx        To:       ccielab@xxxxxxxxxxxxxx                                                        
                      .com>                    cc:                                                                                     
                      Sent by:                 Subject:  3550 root guard and loop guard                                                
                      06-11-2002 16:45                                                                                                 
                      Please respond to                                                                                                
                      "Szeto Jeff"                                                                                                     

Hi Group,

I am reading the config guide and do not clear about the root and loop

Why root guard prevent the remote switch that connecting to the local switch
from becoming the root?
The following, about the loop guard, is copied from the guide:
"You can use loop guard to prevent alternate or root ports from becoming
designated ports because of a failure that leads to a unidirectional link"
Actually, what the loop guard do?

Thank you in advance.


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