VLAN communication with another IP range

HI,

I'm busy setting up new infrastructure/servers with new Dell layer 3 switches. I've created VLANs and a new server IP range that needs to communicate with the old infrastructure to bring resources over. There are no VLANs in the old infrastructure, the switches are layer 2 devices.

I"ve configured VLAN 100 with routing and VLAN IP 10.10.100.1 and subnet 255.255.255.0

My servers can ping the VLAN IP and each other fine.

I need to be able to access another network range (old infrastructure) 172.16.1.X and 172.16.0.X with subnet 255.255.248.0

What I've done:

On VLAN 100, I created a secondary IP of 172.16.0.1 with subnet 255.255.248.0 (which is the gateway IP of the other network. On my servers in VLAN 100, I add another gateway of 172.16.0.1.

I'm now able to ping 172.16.1.X range. But on my layer 3 switch I'm getting errors.

Please see attachment.