Unit 1: Network Infrastructure
This will allow you to demonstrate your networking skills, knowledge, and abilities, with a focus on enterprise-level switching, routing, and multicast components that support cross-platform (inter)operability and integration with the most recent software-defined technologies.
The spanning-tree loopguard feature stops bridging loops that are caused by unidirectional links. If you don’t know, a unidirectional link is one that can only go in one way. Lets say there is a fiber link going from two switches to each other. One wire sends signals, and the other one gets them. If one of the wires in the pair breaks or the gear isn’t working right, one switch might send frames but not receive them, or the other way around. In a layer two looped world, that kind of thing is very dangerous and can lead to bridging loops. That’s what Loopguard can help to solve the problems.
Please keep in mind that loopguard does not prevent unidirectional links or change anything about the unidirectional link itself. When a unidirectional link is present, Loopguard only makes small changes to spanning-tree to work with it. UDLD, which stands for “unidirectional link detection,” is another function that can find the unidirectional link at layer 1 and can take action by doing errdisable on the link. But if UDLD is not turned on and there is a unidirectional link in a looped layer 2 network, loopguard can help stop a bridge loop by taking action.
Unidirectional Link With No Loopguard
Let’s look at our current diagram below:-
Specifically, Cat1 serves as the root bridge of our spanning tree in this instance. The regular STP convergence process causes Cat2’s Fa0/19 to be in the blocking state. This is due to the fact that Fa0/19 is neither a root nor a designated port. On any particular segment, the switch that has the designated port on that segment will send BPDUs on to the segment, and the switch that does not have the designated port on the segment will hear those BPDUs. This is something that you will remember if you are familiar with STP. As a result, in the scenario that we are examining, Cat3 will be sending BPDUs to Cat2. Cat3 is responsible for relaying BPDUs that are passed down from the root bridge. Also we are using PVSTP+ here.
