Catalyst 3850 cannot communicate with SG550XG-8F8T via 10Gb SFP +

[Sergey Lubenkov]

Hi,

I have just installed 2 Catalyst 3850 switches in the stack  and trying to connect them to another 2 Cisco SG550XG-8F8T  switches via 10Gb SFP+ interfaces but they don't really like each other. Both constantly complaining about flapping interfaces and ports getting blocked.  If I am using only one link, both ends show interface up but no traffic flow between them except CDP.  I've tried both trunk and access port, tried even disable spanning tree on 500 switch but still have the same issue.

Connection between those switches via regular 1Gb Ethernet works fine.

Do you guys know what could cause that?

Thank you

[Reza Sharifi]

Hi,

Are you using the correct SFP+ (MM or SM) on both sides of the connection?

How about the fiber patch?

HTH

[Sergey Lubenkov]

It should be correct. I’ve ordered them together with switch. Is there any compatibility matrix available? 

Sorry, I don’t have a fiber.

[balaji.bandi]

adding to other post, 

can you post the logs and configuration if possible. also show spanning-tree block from cisco 3850

do you have UDLD enable on 3850 ?