I am having a strange problem that I have not yet been able to resolve, I have done a fair bit of testing before posting this as it may get me a faster solution.
Currently I have a 3750 Switch with a number of Vlans, one of the Vlan's has a Cisco 1900 ISP feed router attached and all working fine, Routing via this switch is all working as expected.
Here's the problem.
I am replacing the 3750 with a 3850 stack and copy most of the configuration across, I say most as a few commands are no longer supported on the 3850.
I connect the Cisco 1900 ISP feed router as I had previously however now the Internet does no longer work, everything else is fine, from my client Vlan I can still ping the Vlan Interface the Cisco 1900 is connected to but I cannot ping the router from a client Vlan.
I can ping the Cisco 1900 router from the Cisco 3850 switch and I can ping the Internet from the 3850 Switch through the Cisco 1900.
If I connect a laptop to the same Vlan as the Cisco 1900 router and give it for example the IP address of the router I can ping the Laptop from the client Vlan suggesting to me there is no routing problem, however when I re-connect the Cisco 1900 I cannot ping it even though it's the same IP.
The router is pingable as I can ping it from the 3850 switch.
If I connect a laptop to the same Vlan as the Cisco 1900 and give it an IP in the same range and specify the router as my default gateway I can connect to the Internet.
From my client Vlan I can ping the Laptop but not the Cisco 1900 router.
What's going on, am I loosing it or is there a subtle command that I need to type on the Cisco 3850 to make this work.
Any suggestion however small as I'm currently going round in circles.
Thanks in advance.