How to send a UDP packet if there are multiple NICs in the system?

Question

Python

I need to send a UDP packet to a device connected to my workstation via Ethernet. The difficulty is that this device only supports the network protocol stack to a limited extent, in particular, there is no support for ARP.
I expect to get around this limitation by manually adding an entry to the ARP cache (arp -s ).
There are several network cards in the system, how does the OS determine from which of them the UDP packet will be sent?
How can I send a UDP packet from a network card from a python?

Answer 1

the routing table contains all the necessary information