what is loopguard , BPDUguard , Rootguard ?

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Oct 4th, 2010
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I am always confused about these three concepts.

I just want to know the basic understanding of this three features of STP.

where should i use and which mode i can configure this ?

I referred cisco website for the same but still not cleared about it ............

Please share the knowledge . It would be great help for getting cleared this concepts ....................

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arjmenon Mon, 10/04/2010 - 04:00
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Hi ,

These features are documented in http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.1E/native/configuration/guide/stp_enha.html#wp1034195and%20check%20configuring%20STP%20features


pdu guard, portfast are configured at the access layer so that the interface transitions into the forwarding state immediately in order to
avoid unnecessary TCN changes. These ports should see only end-station traffic so we configure these features here.

The device which is configured as the root in the network, in order to ensure that it remains the root and is not affected by changes in the
network we can configure root guard, loop guard.

Loop guard should be enabled on ports at any layer where there is a chance of a loop happening. This 
could be at access, distribution ,core layers.

Root guard is enabled on ports where you don't expect a superior BPDU to be recieved on . Lets say you have 
A as the root , and so if someone connects a switch which has a lower pri than the current root, it is going
to advertise iteself as root , so lets say you have rootguard configured on the B-C link then it will put
the link into root-inconsistent state .

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So again, it depends on your topology you have in place and what features you would like to implement.
Arjun Menon


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