vlan potential conflict question

Hello!

Looking at your description of the problem I would say there wouldn't be a conflict between them.

Yes devices in vlan 1 will not be able to access the devices on the new vlan.  The reason being is that if some on the /24 vlan attempts to connect to the /16 on vlan 1 the packet will flow properly to the /16 device.  However, when the /16 device attempts to connect to the /24 device the IP stack on that device will match the destination Ip address with its own subnet mask /16.  Given that it will assume that the destination is on the same network as itself.  It will then send out a broadcast ARP for the mac address which will only go out on vlan 1.  It will not forward the packet to its default gateway to reach the new vlan, as it will believe that the new vlan is part of its own network.  So essentially you will only get 1 way traffic.  From the new vlan to vlan 1.  Now it may be that proxy arp on the layer 3 router might help you here, but I would not recommend this setup.

You have two separate virtual lans and two separate subnets. Even if you put them on the same physical network, they wouldn't conflict or even communicate. Putting them on VLANS is what you need to do, in order for the L3 switch or router to allow communications between them.

Hmm we seem to have conflicting ideas here. I have layer 3 switch in place which does the intervals routing so would this allow it to work or does the /16 as you said presume traffic to the /24 network is it's own LAN?

Cheers perfect confirmed what I believed