Loop Guard - Thoughts on Best Practices, Where to Use

Answered Question
Nov 8th, 2011

Hi All -

I'm looking for thoughts on best practices w.r.t. which interfaces 'spanning-tree guard loop' should be configured on.

If a particular access switch has two uplinks to the same distro switch, and these are bundled in a Port Channel, is there a benefit to configuring loop guard on each of the physical ports which make up the Po?  Under the config of the Po interface?

Thanks

Nick

I have this problem too.
0 votes
Correct Answer by Mohamed Sobair about 2 years 5 months ago

Hello,

Loop Guard is a feature intended to provide additional check to prevent STP bridging loop, in order for a port to remian on blocking STP state, it needs to continously recieves BPDU from the upstream designated port. If the Blocking port for any reason fails to recieve STP BPDUs, the port will move to STP forwarding State and would therfore create a loop. So, where STP Loop Guard Feature should be configured, the most obvious answer is on the Blocking STP ports.

Its the ports (Alternate Blocking) and (Root Ports) where STP Loop Guard should be enabled.

However, if you have a single portchannel to a distribution Switch, you Dont need Loop Guard feature here. You would need it if your Access Switch has 2 uplinks to two different distribution Switches.

HTH

Mohamed

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Correct Answer
Mohamed Sobair Tue, 11/08/2011 - 09:41

Hello,

Loop Guard is a feature intended to provide additional check to prevent STP bridging loop, in order for a port to remian on blocking STP state, it needs to continously recieves BPDU from the upstream designated port. If the Blocking port for any reason fails to recieve STP BPDUs, the port will move to STP forwarding State and would therfore create a loop. So, where STP Loop Guard Feature should be configured, the most obvious answer is on the Blocking STP ports.

Its the ports (Alternate Blocking) and (Root Ports) where STP Loop Guard should be enabled.

However, if you have a single portchannel to a distribution Switch, you Dont need Loop Guard feature here. You would need it if your Access Switch has 2 uplinks to two different distribution Switches.

HTH

Mohamed

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Posted November 8, 2011 at 7:40 AM
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