I observed that my loopback is 154.54.1.1/32, I sit between AS1 (peer via eth0) and ACM (customer via eth1), and link addresses (10.0.2.x, 10.0.3.x) are point-to-point scoped. I installed a default route via AS1 and customer routes (198.82.0.1, 198.82.0.254, 10.0.4.0/30) via ACM's gateway at 10.0.3.2, all with `src 154.54.1.1`. I chose loopback sourcing because link addresses aren't advertised network-wide, so remote nodes can't route replies back to them. All pings passed with 0% loss (~30-40ms RTT), confirming the configuration is correct. I notified AS1 and ACM of my loopback so they could install return routes. No faults or relay queries arose.