Network Management

Hello Guys,

Sorry I am new to this and so please bear with me. 

So Am I to understand for STP to work correctly that every switch on the network needs to have STP enabled as well? Because I plug-in a new 6300 switch to another 6200 switch that has STP enable, the 6300 come up and going down and bring down the 6200 as well. 

I was able to make it work by enabling STP on the 6300 and everything  is running as it should be.

But here is the kicker: Let's say I have 3 switches and two of them has STP enable and the last one does not(Let's called it Switch 3). If I try to hard set a VLAN to port 45 on Switch 3, the network goes down again. But if I enable STP on switch 3 it works again. I am not sure why because there should not be any loop in my network if I have 3 switches.

Maybe I don't have a clear understanding of Spanning Tree of CX switch, can someone help me understand it better.

Also, is there a better way to see the log on a switch to determine the error using cli?

Thanks

Oumar

Hello oumar
STP is all about transmitting and receiving special frames ("BPDU") between switches.
If all switches are STP enabled (nowadays, should be RSTP or MSTP) they kind of "learn" the topology and one of them will administratively "open" the loop on one interface.

If switch3 does not run STP protocol, either :

• it will pass the BPDU as-is, then the loop protection should occur.
• it will "filter" these BPDU, and the other switches will loose the topology information carried by these frames.

Also keep in mind that there may be a "convergence delay" when connecting switches. Be sure to wait for 30 to 60 seconds before concluding that it does not work.(in MSTP network, there should be quite no delay)

On CX switches (MSTP):
update them to a recent firmware.

check which switch is the "root bridge"
    show spanning-tree summary root
    
    as a good practice, you should set (define) the root bridge by assigning a lower priority :
    spanning-tree priority 0
    
check the status of each interface
    show spanning-tree detail
    show spanning-tree mst
        also check the "Number of topology changes" : in a stable network, this number (may be non-zero) must not change 
    show spanning-tree summary port

You can get additionnal help in "AOS-CX 10.12 Layer-2 Bridging Guide", especially chapter 8 "Spanning Tree protocols (STP)" and sub-section "MSTP debugging and troubleshooting"