ODBC connection to what type of database? SQL Server (port 1433 is standard).

Have you tried re-creating the connection just incase something got messed up. Are you sure the Draytek isn't using that port for something. Can you ping it / tracert to it?

to simulate connection you could use iperf on a its default or another port event the pSQL port on another device for instance.

https://www.dell.com/support/kbdoc/en-us/000139427/how-to-test-available-network-bandwidth-using-iperf

or use wireshark

maybe a bigger subnet encapsulating the smaller correct one??????