@Victoria Smiley, thanks for the question!
The router behavior is as follows:
a) If a service route is configured with a gateway, router ARPs for that gateway and will use the gateway MAC in all requests bound for the connected subnet and beyond.
b) If a service route is configured without a gateway, the treatments of in-subnet and off-subnet traffic are different:
- If the destination IP is in-subnet, router ARPs for the destination and uses the resolved MAC to send traffic to that IP.
- If the destination IP is off-subnet, router ARPs for the gateway configured on the interface and sends traffic to the gateway.