Spanning-tree portfast edge & network


(Cecil B) #1

Hello Rene,
I received one of the virl switch images and was building a lab testing spanning tree. Can you tell me what is the difference between the commands listed below:

#spanning-tree portfast edge 
#spanning-tree portfast network
#spanning-tree normal  

and when should you use which one? Also i read the lessons on both spanning-tree uplinkfast and spanning-tree backbonefast. Both commands seem to do the same thing , fast convergence if a link or indirect link fails. Maybe i am not understanding the lessons. Is there a preference in using one over the other? Can both commands be enabled at the same time on a switch?
Thakns again,
Cecil


(Lazaros Agapides) #2

Hello Cecil!

I’ll go through your questions below.

  • portfast edge is used to configure a port on which an end device is connected, such as a PC. All ports directly connected to end devices cannot create bridging loops in the network. Therefore, the edge port directly transitions to the forwarding state, and skips the listening and learning stages. However, the specific command configures a port such that if it receives a BPDU, it immediately loses its edge port status and becomes a normal spanning-tree port.
  • You use the portfast network on trunk ports to enable bridge assurance feature which protects against loops by detecting unidirectional links in the STP topology. But normally bridge assurance is enabled by default.
  • A spanning tree normal port is one that functions in the default manner for spanning tree. Under normal circumstances it will transition from the Listening, Learning, Forwarding stages based on the default timers.

The major difference between the two is the following:

  • Uplinkfast is used when you want to quickly enable the blocked port on a switch when the root port link has failed.
  • Backbonefast is used when the switch under normal circumstances doesn’t have a blocked port and the root port receives an inferior BPDU. Essentially, it is used to quickly recalculate after an indirect link failure, that is, when a bridge has to change the status of some of its ports because of a failure on a link that is not directly attached to it.

You can find more detailed information about these two features and how to configure them in the following two links:


I hope this has been helpful!

Laz


(Cecil B) #3

Hello Lazaros,
Thanks for answering my question. You have cleared things up for me. Also thanks for the additional reading info…