Adding a non-STP switch to an existing STP switching environment

[selva Kathir]

Hi,

  Hi i have existing setup of STP switches.when i connect a non stp switch to this network as a edge switch . The connected port of my stp enabled switch goes to blocked state and that link is not coming  up . Can get a reason for this  ???

Thanks in advance .

[Giuseppe Larosa]

Hello Selva,

the new switch is not speaking PVST, but it likely runs a form of STP.

Is the port of your device configured for stp bpdu guard ?

you can check the log messages on the switch with

show log

to see why the port is not operational. It is likely put in error disable by STP bpdu guard detecting a received BPDU on link or the so called non STP switch has sent back an STP bpdu received on another port as a multicast frame (flooded)

Also

show spanning-tree inconstistent-ports

for loop guard or root guard activity.

Hope to help

Giuseppe

[selva Kathir]

Hi Giuseppe,

   Thanks for your reply ,the new switch is not at all configured with STP. And the links between both (Non stp &  stp switch ) are configured as trunk . And there is only one link connecting both stp & non stp switches .

thanks,

selva.

[Giuseppe Larosa]

Hello Selva,

is the STP switch a Cisco switch, what model?

if so, try to use show log to understand why the port is not operational?

Is the port up/down?

you may need the following command in interface config mode:

switchport nonegotiate

Sometimes when connecting to other vendor devices the command listed above is needed

Hope to help

Giuseppe

[selva Kathir]

Hi,

I sure that there is no hardware problems . correct me if i am wrong what i am suspecting is stp switch which is not allowing non stp switch to connect to STP network .

Can you please explain what actualy happens when  a  non stp switch is conneced to a STP network .

thanks ,

Selva .

[Giuseppe Larosa]

Hello Selva,

you need to understand if it is a physical layer issues first.

I tried to ask you some details of your switch but you are not providing them

STP comes to play later and the STP switch does not block a non STP device by default

My guess is that the link is not operational for some issues with DTP (hence the suggestion switchport nonegotiate)

Most ot the times issues are at physical layer.

So I suggest to post

show interface type x/y

where type x/y is the interface of STP switch connecting to non STP switch

Can you do this?

Hope to help

Giuseppe

[selva Kathir]

Hi ,

I am out of office now as soon as i reach office i will post those outputs

thanks for your response .

selva .