The difference between BLK or LBK - STP status causing self-looped

[mhiyoshi]

Dear all,

I have been looking for exact document when Router's STP self-looped happen on the Switch Port.

So generally if the original BPDU returns in its Catalyst switch itself then the port status changes to BLK with self-loop right? 

However if the case is Router for instance Cisco891F recognize as LBK with self-loop.

So I would just like to know whether these two status are same role or not and it just shows the different status as BLK or LBK.

Best Regards,

Masaonbu Hiyoshi

[balaji.bandi]

BLK - STP loop detected then one of the port in Blocking mode, other one in forward mode.(depends on how you configure.

As for i know the LBK you referring as below :

LBK state represents Loop-Back state.  

If you have connected balun cable to this port then this can be in LBK mode, balun cable is a loopback cable.

Make Sense ?

[mhiyoshi]

Hi Balaji,

Thank you very much. Yes I agree to your comment however as for Cisco891 Router's switch port is little bit different from Catalyst Switch, for example if the loop happen within HUB to C891F Gi0(Switchport)

then while loop is occurring then C891F keeps the STP status as LBK but if the HUB loop is removed after that the status changes from LBK to BLK. and not change in my verification.

So I think the purpose of both status is just to block the port right? 

Best Regards,

Masanobu Hiyoshi