440-g2 suddenly lost connection to B5 via fiber connection same subnet

[ctg023]

I’m having an issue with a fiber connection between a 440-g2 and a B5 switch in the same building. Everything was fine then the connection between the 2 were lost unexpectedly. All other devices plugged into the 440-g2 on vlan 1 works fine. 

After several hours of troubleshooting, I was able to create a strange workaround by plugging in a spare B5 into the 440-g2 via an ethernet cable (nothing else is plugged into the spare B5), now I can ping across the fiber from the 440-g2, not sure why though.

Does anyone have any ideas why the fiber only works with another B5 is plugged into the 440-G2? 

[ctg023 · Accepted solution]

Stefan, 

You pointed me in the right direction and I believe it is now able to communicate without the additional B5 switch being connected. Had to enable STPD on the 440-G2 for the port using the fiber connection. 
Here are the commands I ran to fix it. 

configure stpd s0 ports link-type edge <port connected to fiber>
configure stpd s0 ports edge-safeguard enable <port connected to fiber>
configure stpd s0 ports bpdu-restrict enable <port connected to fiber>
enable stpd s0

I’ll keep an eye on it and see if any other issues arise with this configuration. If I run into issues, I’ll update the thread. 

[ctg023]

Hi Stefan,
Thanks for taking time to reply. STP is disabled on the 440-g2, but is enabled by default on the B5’s so that would make sense on why plugging in the B5 to the 440-g2 works. I’m still unsure on why the original connection stopped working though and still investigating, with my limited knowledge on 440-g2’s. Any help is appreciated. 

[Stefan_K_]

Hello,

do you maybe use spanning tree and plugging in the B5 initiated a spantree topology change, which fixed a STP-problem, that blocked the downlink-port to the B5?