Why portfast cisco

Spanning-tree will send a topology change notification on the interface towards SW2 and the counter will increase:. In short, everytime we unplug the cable the switch will generate a TCN. If you like to keep on reading, Become a Member Now! Here is why:. Your articles are so useful, it totally saved me. It takes too much time to create a startup config for any possible method.

Thanks for this explanation. Ask a question or join the discussion by visiting our Community Forum. Now, that old switch is going to become the root bridge and you want to make sure that this should not happen. Another reason that the wrong switch could become a root bridge is maybe that you're under an attack. What the attacker will do is put a switch in the network, trying to make that the root bridge to force traffic to come through the switch that they're controlling.

They'll then be able to sniff the traffic and gain access to sensitive information. So, if you want to make sure that the current root bridge remains your root bridge, you can use Root Guard to help ensure that. The way it works is if a port was Root Guard is enabled when it receives BPDUs that superior to the current root bridge, it will transition that port to root-inconsistent.

There will be no traffic forwarded over that port. The way that you configure this is on the interface configuration mode, you enter the command:. In our example, we've got our root bridge up in the top left. This is the one that we want to remain the root bridge. Now, if a switch at the bottom starts sending out superior BPDUs, they are not going to be accepted and the port that is connected to that switch is going to be transitioned to root-inconsistent, basically shutting the port down.

You are concerned that a user may introduce a loop into the network by adding additional switches or changing the cabling. Also ensure that the ports where Spanning Tree is disabled will be automatically shut down if a switch is detected on the other side of the link.

With a mission to spread network awareness through writing, Libby consistently immerses herself into the unrelenting process of knowledge acquisition and dissemination. If not engrossed in technology, you might see her with a book in one hand and a coffee in the other.

Alancha Thompson. Libby Teofilo. These two features enhance network reliability, manageability, and security for the existing L2 STP feature. The PortFast feature is introduced to avoid network connectivity issues.

These issues are caused by delays in STP enabled ports moving from blocking-state to forwarding-state after transitioning from the listening and learning states.

STP enabled ports that are connected to devices such as a single switch, workstation, or a server can access the network only after passing all these STP states. Some applications need to connect to the network immediately, else they will timeout.