Well, the 3750 is a switch so one idea would be to connect the devices directly to the switchports instead of using the one you call "L1 device", this way the ports will learn the MAC of those devices and they will belong to the same VLAN that by default is VLAN 1. The IP address that is currently on the second port will now be assigned to "interface vlan 1"
I'm not sure if what you are trying to achieve is something like this?
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...