STP an switching loops...

[porress]

I have been reading the cisco docs and ok STP prevents loops on the network, I have tested it on my network and it is true, it works. My question is...

What happends when i put a path cable on port 21 on one switch and the other end of the same cable in 22 when PortFast or Edge Port is enable? I have tried it a port 21 says Forwarding and the other one says Backup. And both ports flash but why does it flash? is it not being blocked?

 

[leedsit]

What do you mean by Flash???

If you plug port 21 which is a non port fast/edge port into port 22 which is a port fast/edge port then a loop would occur unless you have BDPU Guard or BDPU filtering enabled on port 22..... not sure what the default is on your switch.

LEEroy
MCNE6,CCNA2,CWNA, Project+

 

[baddos]

Do a show spanning-tree interface (portnum) to see what the port is doing.