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It's time for us to cover the second set of enhancements that Cisco made to

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Spanning

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Tree which involve two different techniques.

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They are UDLD, Unidirectional Link Detection and Loop Guard.

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Now oftentimes we look at that along with Root Guard and BPDU Guard.

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We've got all of these different special features.

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We're just trying to keep them straight in our heads.

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What do they all do?

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And so it's important for us to recognize that there is this dividing line so

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to speak.

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We just covered the concept of topology protection.
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We just covered the concept of topology protection.

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Root Guard and BPDU Guard are all about making sure that our root stays the

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root.

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That we don't make switches that just show up on the network into the root and

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cause

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a whole convergence event and all of those kinds of things.

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So we protect our root.

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We protect ourselves from unauthorized BPDUs and especially switches connecting

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.

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That's topology protection.

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But now we have another situation on our hands.

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We have all of these protection mechanisms to protect loops.

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So it's the whole point of Spanning Tree is to protect our network from loops.
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So it's the whole point of Spanning Tree is to protect our network from loops.

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And yet there are a few very corner case scenarios where loops can form.

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And we could roll the dice and say, "Hey, hopefully none of these scenarios

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ever happen

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to us."

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It's like saying we were at a 99, maybe even 99.99% success rate at protecting

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loops.

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Is that good enough?

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Well, for a lot of organizations, unless it's 100%, it's not good enough.

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And that should be our perspective.

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Even if some of these scenarios are unlikely to occur, they could occur and
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Even if some of these scenarios are unlikely to occur, they could occur and

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they could

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create loops even though we're running Spanning Tree protocol.

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So Cisco recognized that there are a few flaws with the Spanning Tree logic and

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those

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flaws continue to exist even within the world of rapid Spanning Tree.

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So just like with the topology protection mechanisms, these loop protection

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mechanisms

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were about to cover, UDLD and loop guard, these are going to be useful to us

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even as

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we move into a rapid Spanning Tree and potentially MST if we're running it.

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But again, let's think about it in two separate groups.
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But again, let's think about it in two separate groups.

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We've got our topology protection group over here.

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We've already covered that.

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Now it's time to jump into our loop protection.

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We want to look at the very few cases where Spanning Tree doesn't quite cut it

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and use

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these techniques in order to ensure that even in those scenarios we don't

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create loops on