Connecting Fiber trunk port Cisco 3650 to 3750

[HRahman]

I encountered a problem and managed to fix it but I do not understand how it worked. I had replaced an older switch (2960) to a 3650. The old switch had it's port 24 (fiber) configured in trunk mode connected to a 3650 switch port gi1/1/3. After replacing the 2960 to a new 3650, I connected the fiber port to gi1/1/1 (which is connecting to the other 3650 switch port gi1/1/3). Although devices were pingable, there was latency and packet drops. I tried to switch to the second port. Now gi 1/1/2 is connected to gi 1/1/3 on the other switch. This time, the ping was stable but some applications like file transfer and remote desktop were extremely slow and had disconnection. Lastly, I changed the fiber port to 1/1/3 and it started working perfectly. It will be helpful if anyone could provide any insights.

[Mark Malone]

Hi
did you collect any outputs from the interfaces as the issues were occurring , any traces , interface outputs etc , could be many reasons but they would be the first things to check , without that information were just guessing really , traceroutes would be important for the latency so you could see the hop where the slowness occurred and then you could investigate that device or interface

As the device is new you could still check the interfaces you were connected to if they were only used for that once an see if there were any bad error counts on the ports but to check latency you need traceroute to see the path output