ASR9K support STP

[Network Digger]

Hi there,

I was checking the datasheets of the ASR9K and found the router supports MST (multiple spanning tree protocol), I am not sure what is the use case of a router to support STP in general, since routers don’t forward broadcasts so there is no need to eliminate loops by STP, or am I missing something??

thanks. 

[Jaderson Pessoa]

Yes, you has right. But this model support this to provide better solution in some case. For exemple:



If an L2 interface or subinterface is configured with an encapsulation that matches multiple VLANs, then all of those VLANs must be mapped to the same spanning tree instance. There is therefore a single spanning tree instance associated with each L2 interface or subinterface.
All the interfaces or subinterfaces in a given bridge domain must be associated with the same spanning tree instance.
Multiple subinterfaces on the same interface must not be associated with the same spanning tree instance, unless those subinterfaces are in the same split horizon group. In other words, hair-pinning is not possible.
Across the network, L2 interfaces or subinterfaces must be configured on all redundant paths for all the VLANs mapped to each spanning tree instance. This is to avoid inadvertent loss of connectivity due to STP blocking of a port.

[Network Digger]

Hi Jaderson, thanks a lot for your feedback, but sorry I am not able to follow exactly, could you explain it in more details please if possible?? thank you.